draft-ietf-tsvwg-sctpthreat-05.txt   rfc5062.txt 
<.
Network Working Group R. Stewart Network Working Group R. Stewart
Internet-Draft Cisco Systems, Inc. Request for Comments: 5062 Cisco Systems, Inc.
Expires: December 15, 2007 M. Tuexen Category: Informational M. Tuexen
Muenster Univ. of Applied Sciences Muenster Univ. of Applied Sciences
G. Camarillo G. Camarillo
Ericsson Ericsson
June 13, 2007 September 2007
Security Attacks Found Against SCTP and Current Countermeasures
draft-ietf-tsvwg-sctpthreat-05.txt
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This Internet-Draft will expire on December 15, 2007. Security Attacks Found Against
the Stream Control Transmission Protocol (SCTP)
and Current Countermeasures
Copyright Notice Status of This Memo
Copyright (C) The IETF Trust (2007). This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Abstract Abstract
This document describes certain security threats to SCTP. It also This document describes certain security threats to SCTP. It also
describes ways to mitigate these threats, in particular by using describes ways to mitigate these threats, in particular by using
techniques from the SCTP Specification Errata and Issues memo (RFC techniques from the SCTP Specification Errata and Issues memo (RFC
4460). These techniques are included in RFC 4960, which obsoletes 4460). These techniques are included in RFC 4960, which obsoletes
RFC 2960. It is hoped that this information will provide some useful RFC 2960. It is hoped that this information will provide some useful
background information for many of the newest requirements spelled background information for many of the newest requirements spelled
out in the SCTP Specification Errata and Issues and included in RFC out in the SCTP Specification Errata and Issues and included in RFC
4960. 4960.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Address Camping or stealing . . . . . . . . . . . . . . . . . 3 2. Address Camping or Stealing . . . . . . . . . . . . . . . . . 2
3. Association hijacking 1 . . . . . . . . . . . . . . . . . . . 5 3. Association Hijacking 1 . . . . . . . . . . . . . . . . . . . 3
4. Association hijacking 2 . . . . . . . . . . . . . . . . . . . 7 4. Association Hijacking 2 . . . . . . . . . . . . . . . . . . . 6
5. Bombing attack (amplification) 1 . . . . . . . . . . . . . . . 8 5. Bombing Attack (Amplification) 1 . . . . . . . . . . . . . . . 7
6. Bombing attack (amplification) 2 . . . . . . . . . . . . . . . 10 6. Bombing Attack (Amplification) 2 . . . . . . . . . . . . . . . 9
7. Association redirection . . . . . . . . . . . . . . . . . . . 11 7. Association Redirection . . . . . . . . . . . . . . . . . . . 10
8. Bombing attack (amplification) 3 . . . . . . . . . . . . . . . 11 8. Bombing Attack (Amplification) 3 . . . . . . . . . . . . . . . 10
9. Bombing attack (amplification) 4 . . . . . . . . . . . . . . . 12 9. Bombing Attack (Amplification) 4 . . . . . . . . . . . . . . . 11
10. Bombing attack (amplification) 5 . . . . . . . . . . . . . . . 12 10. Bombing Attack (amplification) 5 . . . . . . . . . . . . . . . 11
11. Security Considerations . . . . . . . . . . . . . . . . . . . 13 11. Security Considerations . . . . . . . . . . . . . . . . . . . 12
12. IANA considerations . . . . . . . . . . . . . . . . . . . . . 13 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
13.1. Normative References . . . . . . . . . . . . . . . . . . 13
13.2. Informative References . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14
Intellectual Property and Copyright Statements . . . . . . . . . . 16
1. Introduction 1. Introduction
Stream Control Transmission Protocol originally defined in [RFC2960] Stream Control Transmission Protocol, originally defined in
is a multi-homed transport protocol. As such, unique security [RFC2960], is a multi-homed transport protocol. As such, unique
threats exists that are addressed in various ways within the protocol security threats exists that are addressed in various ways within the
itself. This document describes certain security threats to SCTP. protocol itself. This document describes certain security threats to
It also describes ways to mitigate these threats, in particular by SCTP. It also describes ways to mitigate these threats, in
using techniques from the SCTP Specification Errata and Issues memo particular by using techniques from the SCTP Specification Errata and
([RFC4460]). These techniques are included in Issues memo [RFC4460]. These techniques are included in [RFC4960],
[I-D.ietf-tsvwg-2960bis], which obsoletes [RFC2960]. It is hoped which obsoletes [RFC2960]. It is hoped that this information will
that this information will provide some useful background information provide some useful background information for many of the newest
for many of the newest requirements spelled out in the [RFC4460] and requirements spelled out in the [RFC4460] and included in [RFC4960].
included in [I-D.ietf-tsvwg-2960bis].
This work and some of the changes that went into the [RFC4460] and This work and some of the changes that went into [RFC4460] and
[I-D.ietf-tsvwg-2960bis] are much indebted to the paper on potential [RFC4960] are much indebted to the paper on potential SCTP security
SCTP security risks Effects [effects] by Aura, Nikander and risks [EFFECTS] by Aura, Nikander, and Camarillo. Without their
Camarillo. Without their work some of these changes would remain work, some of these changes would remain undocumented and potential
undocumented and potential threats. threats.
The rest of this document will concentrate on the various attacks The rest of this document will concentrate on the various attacks
that were illustrated in Effects [effects] and detail what that were illustrated in [EFFECTS] and detail the preventative
preventative measures are now in place within the current SCTP measures now in place, if any, within the current SCTP standards.
standards (if any).
2. Address Camping or stealing 2. Address Camping or Stealing
This attack is a form of denial of service attack crafted around This attack is a form of denial of service attack crafted around
SCTP's multi-homing. In effect an illegitimate endpoint connects to SCTP's multi-homing. In effect, an illegitimate endpoint connects to
a server and "camps upon" or holds up a valid peers address. This is a server and "camps upon" or "holds up" a valid peer's address. This
done to prevent the legitimate peer from communicating with the is done to prevent the legitimate peer from communicating with the
server. server.
2.1. Attack details 2.1. Attack Details
+----------+ +----------+ +----------+ +----------+ +----------+ +----------+
| Evil | | Server | | Client | | Evil | | Server | | Client |
| IP-A=+------------+ +-----------+=IP-C & D | | IP-A=+------------+ +-----------+=IP-C & D |
| Attacker | | | | Victim | | Attacker | | | | Victim |
+----------+ +----------+ +----------+ +----------+ +----------+ +----------+
Figure 1: Camping Figure 1: Camping
Consider the scenario illustrated in Figure 1. The attacker Consider the scenario illustrated in Figure 1. The attacker
legitimately holds IP-A and wishes to prevent the 'Client-Victim' legitimately holds IP-A and wishes to prevent the 'Client-Victim'
from communication with the 'Server'. Note also that the client is from communicating with the 'Server'. Note also that the client is
multi-homed. The attacker first guesses the port number our client multi-homed. The attacker first guesses the port number our client
will use in its association attempt. It then uses this port and sets will use in its association attempt. It then uses this port and sets
up an association with the server listing not only IP-A but also IP-C up an association with the server listing not only IP-A but also IP-C
as well in its initial INIT chunk. The server will respond and setup in its initial INIT chunk. The server will respond and set up the
the association noting that the attacker is multi-homed holding both association, noting that the attacker is multi-homed and holds both
IP-A and IP-C. IP-A and IP-C.
Next the victim sends in an INIT message listing its two valid Next, the victim sends in an INIT message listing its two valid
addresses IP-C and IP-D. In response it will receive an ABORT addresses, IP-C and IP-D. In response, it will receive an ABORT
message with possibly an error code indicating that a new address was message with possibly an error code indicating that a new address was
added in its attempt to setup an existing association (a restart with added in its attempt to set up an existing association (a restart
new addresses). At this point 'Client-Victim' is now prevented from with new addresses). At this point, 'Client-Victim' is now prevented
setting up an association with the server until the server realizes from setting up an association with the server until the server
that the attacker does not hold the address IP-C at some future point realizes that the attacker does not hold the address IP-C at some
by using a HEARTBEAT based mechanism. See the mitigation option future point by using a HEARTBEAT based mechanism. See the
subsection of this section. mitigation option subsection of this section.
2.2. Analysis 2.2. Analysis
This particular attack was discussed in detail on the SCTP This particular attack was discussed in detail on the SCTP
implementors list in March of 2003. Out of that discussion changes implementors list in March of 2003. Out of that discussion, changes
were made in the BSD implementation that are now present in the were made in the BSD implementation that are now present in
[I-D.ietf-tsvwg-2960bis]. In close examination, this attack depends [RFC4960]. In close examination, this attack depends on a number of
on a number of specific things to occur. specific things to occur.
1) The attacker must setup the association before the victim and must 1) The attacker must set up the association before the victim and
correctly guess the port number that the victim will use. If the must correctly guess the port number that the victim will use. If
victim uses any other port number the attack will fail. the victim uses any other port number the attack will fail.
2) SCTP's existing HEARTBEAT mechanism as defined already in 2) SCTP's existing HEARTBEAT mechanism as defined already in
[RFC2960] will eventually catch this situation and abort the evil [RFC2960] will eventually catch this situation and abort the evil
attackers association. This may take several seconds based on attacker's association. This may take several seconds based on
default HEARTBEAT timers but the attacker himself will lose any default HEARTBEAT timers but the attacker himself will lose any
association. association.
3) If the victim is either not multi-homed, or the address set that 3) If the victim is either not multi-homed, or the address set that
it uses is completely camped upon by the attacker (in our example it uses is completely camped upon by the attacker (in our example
if the attacker had included IP-D in its INIT as well), then the if the attacker had included IP-D in its INIT as well), then the
client's INIT message would initiate an association between the client's INIT message would initiate an association between the
client and the server while destroying the association between the client and the server while destroying the association between the
attacker and the server. From the servers' perspective this is a attacker and the server. From the servers' perspective, this is a
restart of the association. restart of the association.
2.3. Mitigation option 2.3. Mitigation Option
[I-D.ietf-tsvwg-2960bis] adds a new set of requirements to better [RFC4960] adds a new set of requirements to better counter this
counter this attack. In particular the HEARTBEAT mechanism was attack. In particular, the HEARTBEAT mechanism was modified so that
modified so that addresses unknown to an endpoint (i.e. presented in addresses unknown to an endpoint (i.e., presented in an INIT with no
an INIT with no pre-knowledge given by the application) enter a new pre-knowledge given by the application) enter a new state called
state called "UNCONFIRMED". During the time that any address is "UNCONFIRMED". During the time that any address is UNCONFIRMED and
UNCONFIRMED and yet considered available, heartbeating will be done yet considered available, heartbeating will be done on those
on those UNCONFIRMED addresses at an accelerated rate. This will UNCONFIRMED addresses at an accelerated rate. This will lessen the
lessen the time that an attacker can "camp" on an address. In time that an attacker can "camp" on an address. In particular, the
particular the rate of heartbeats to UNCONFIRMED addresses is done rate of heartbeats to UNCONFIRMED addresses is done every RTO. Along
every RTO. Along with this expanded rate of heartbeating, a new 64 with this expanded rate of heartbeating, a new 64-bit random nonce is
bit random nonce is required to be inside HEARTBEATs to UNCONFIRMED required to be inside HEARTBEATs to UNCONFIRMED addresses. In the
addresses. In the HEARTBEAT-ACK the random nonce must match the HEARTBEAT-ACK, the random nonce must match the value sent in the
value sent in the HEARTBEAT before an address can leave the HEARTBEAT before an address can leave the UNCONFIRMED state. This
UNCONFIRMED state. This will prevent an attacker from generating will prevent an attacker from generating false HEARTBEAT-ACKs with
false HEARTBEAT-ACKs with the victims source address(es). In the victim's source address(es). In addition, clients that do not
addition, clients which do not need to use a specific port number need to use a specific port number should choose their port numbers
should choose their port numbers on a random base. This makes it on a random basis. This makes it hard for an attacker to guess that
hard for an attacker to guess that number. number.
3. Association hijacking 1 3. Association Hijacking 1
Association hijacking is the ability of some other user to assume the Association hijacking is the ability of some other user to assume the
session created by another endpoint. In cases of a true man-in-the- session created by another endpoint. In cases of a true man-in-the-
middle only a strong end-to-end security model can prevent this. middle, only a strong end-to-end security model can prevent this.
However with the addition of the [I-D.ietf-tsvwg-addip-sctp] However, with the addition of the SCTP extension specified in
extension to SCTP an endpoint that is NOT a man-in-the-middle may be [RFC5061], an endpoint that is NOT a man-in-the-middle may be able to
able to assume another endpoints association. assume another endpoint's association.
3.1. Attack details 3.1. Attack Details
The attack is made possible by any mechanism that lets an endpoint The attack is made possible by any mechanism that lets an endpoint
acquire some other IP address that was recently in use by an SCTP acquire some other IP address that was recently in use by an SCTP
endpoint. For example in a mobile network DHCP may be in use with endpoint. For example, DHCP may be used in a mobile network with
short IP address lifetimes to reassign IP addresses to migrant hosts. short IP address lifetimes to reassign IP addresses to migrant hosts.
IP-A DHCP-Server's Peer-Server IP-A DHCP-Server's Peer-Server
| |
| |
1 |-DHCP-Rel(IP-A)---->| 1 |-DHCP-Rel(IP-A)---->|
2 |------ASCONF(ADD-IP(IP-B), DEL-IP(IP-A)---->XXlost 2 |------ASCONF(ADD-IP(IP-B), DEL-IP(IP-A)---->XXlost
time time
| |
|-DHCP-new-net------>| |-DHCP-new-net------>|
skipping to change at page 6, line 27 skipping to change at page 5, line 34
|-------------INIT()------------------------> |-------------INIT()------------------------>
5 |<------------INIT-ACK()--------------------- 5 |<------------INIT-ACK()---------------------
| |
6 |----ASCONF(ADD-IP(IP-Z),DEL-IP(IP-A))------> 6 |----ASCONF(ADD-IP(IP-Z),DEL-IP(IP-A))------>
Figure 2: Association Hijack via DHCP Figure 2: Association Hijack via DHCP
At point 1, our valid client releases the IP address IP-A. It At point 1, our valid client releases the IP address IP-A. It
presumably acquires a new address (IP-B) and sends an ASCONF to ADD presumably acquires a new address (IP-B) and sends an ASCONF to ADD
the new address and delete to old address at point 2, but this packet the new address and delete to old address at point 2, but this packet
is lost. Thus our peer (Peer-Server) has no idea that the former is lost. Thus, our peer (Peer-Server) has no idea that the former
peer is no longer at IP-A. Now at point 3 a new "evil" peer DHCP's peer is no longer at IP-A. Now at point 3, a new "evil" peer obtains
an address and happens to get the re-assigned address IP-A. Our an address via DHCP and it happens to get the re-assigned address
Peer-Server sends a chunk of DATA at point 4. This reveals to the IP-A. Our Peer-Server sends a chunk of DATA at point 4. This
new owner of IP-A that the former owner of IP-A had an association reveals to the new owner of IP-A that the former owner of IP-A had an
with Peer-Server. So at point 5 the new owner of IP-A sends an INIT. association with Peer-Server. So at point 5, the new owner of IP-A
The INIT-ACK is sent back and inside it is a COOKIE. The cookie sends an INIT. The INIT-ACK is sent back and inside it is a COOKIE.
would of course hold tie-tags which would list both sets of tags The cookie would of course hold tie-tags, which would list both sets
which could then be used at point 6 to add in any other IP addresses of tags that could then be used at point 6 to add in any other IP
that the owner of IP-A holds and thus acquire the association. addresses that the owner of IP-A holds and thus acquire the
association.
It should be noted that this attack is possible in general whenever It should be noted that this attack is possible in general whenever
the attacker is able to send packets with source address IP-A and the attacker is able to send packets with source address IP-A and
receive packets with destination address IP-A. receive packets with destination address IP-A.
3.2. Analysis 3.2. Analysis
This attack depends on a number of events: This attack depends on a number of events:
1) Both endpoints must support the [I-D.ietf-tsvwg-addip-sctp] 1) Both endpoints must support the SCTP extension specified in
extension. [RFC5061].
2) One of the endpoints must be using the [I-D.ietf-tsvwg-addip-sctp] 2) One of the endpoints must be using the SCTP extension for mobility
extension for mobility. specified in [RFC5061].
3) The IP address must be acquired in such a way as to make the 3) The IP address must be acquired in such a way as to make the
endpoint the owner of that IP address as far as the network is endpoint the owner of that IP address as far as the network is
concerned. concerned.
4) The true peer must not get the ASCONF packet that deletes IP-A and 4) The true peer must not receive the ASCONF packet that deletes IP-A
adds its new address to the peer before the new "evil" peer gets and adds its new address to the peer before the new "evil" peer
control of the association. gets control of the association.
5) The new "evil" peer must have an alternative address besides IP-A 5) The new "evil" peer must have an alternate address, aside from the
that it can add to the association so it can delete IP-A IP-A that it can add to the association, so it can delete IP-A,
preventing the real peer from re-acquiring the association when it preventing the real peer from re-acquiring the association when it
finally retransmits the ASCONF (from step 2). finally retransmits the ASCONF (from step 2).
3.3. Mitigation option 3.3. Mitigation Option
[I-D.ietf-tsvwg-2960bis] adds a new counter measure to this threat. [RFC4960] adds a new counter measure to this threat. It is now
It is now required that Tie-Tags in the State-Cookie parameter not be required that Tie-Tags in the State-Cookie parameter not be the
the actual tags. Instead a new pair of two 32 bit nonces must be actual tags. Instead, a new pair of two 32-bit nonces must be used
used to represent the real tags within the association. This to represent the real tags within the association. This prevents the
prevents the attacker from acquiring the real tags and thus prevents attacker from acquiring the real tags and thus prevents this attack.
this attack. Furthermore the use of the [I-D.ietf-tsvwg-addip-sctp] Furthermore, the use of the SCTP extension specified in [RFC5061]
extensions requires the use of the authentication mechanism defined requires the use of the authentication mechanism defined in
in [I-D.ietf-tsvwg-sctp-auth]. This requires the attacker to be able [RFC4895]. This requires the attacker to be able to capture the
to capture the traffic during the association setup. If in addition traffic during the association setup. If in addition an endpoint-
an end-point pair shared key is used, capturing or intercepting these pair shared key is used, capturing or intercepting these setup
setup messages does not enable the attacker to hijack the messages does not enable the attacker to hijack the association.
association.
4. Association hijacking 2 4. Association Hijacking 2
Association hijacking is the ability of some other user to assume the Association hijacking is the ability of some other user to assume the
session created by another endpoint. In cases where an attacker can session created by another endpoint. In cases where an attacker can
send packets using the victims IP-address as a source address and can send packets using the victims IP-address as a source address and can
receive packets with the victims' address as destination address the receive packets with the victims' address as a destination address,
attacker can easily restart the association. If the peer does not the attacker can easily restart the association. If the peer does
pay attention to the restart notification the attacker has taken over not pay attention to the restart notification, the attacker has taken
the association. over the association.
4.1. Attack details 4.1. Attack Details
Assume that an endpoint E1 having an IP-address A has an SCTP Assume that an endpoint E1 having an IP-address A has an SCTP
association with endpoint E2. After the attacker is able to receive association with endpoint E2. After the attacker is able to receive
packets with destination address A and send packet with source packets to destination address A and send packets with source address
address A the attacker can perform a full four-way handshake using A, the attacker can perform a full four-way handshake using the IP-
the the IP-addresses and port numbers from the received packet. E2 addresses and port numbers from the received packet. E2 will
will consider this as a restart of the association. If and only if consider this a restart of the association. If and only if the SCTP
the SCTP user of E2 does not process the restart notification the user of E2 does not process the restart notification, the user will
user will not recognize that that association just restarted. From not recognize that the association just restarted. From this
his perspective the association has been hijacked. perspective, the association has been hijacked.
4.2. Analysis 4.2. Analysis
This attack depends on a number of circumstances: This attack depends on a number of circumstances:
1) The IP address must be acquired in such a way as to make the evil 1) The IP address must be acquired in such a way as to make the evil
endpoint the owner of that IP address as far as the network or endpoint the owner of that IP address as far as the network or
local LAN is concerned. local LAN is concerned.
2) The attacker must receive a packet belonging to the association or 2) The attacker must receive a packet belonging to the association or
connection. connection.
3) The other endpoints user does not pay attention to restart 3) The other endpoint's user does not pay attention to restart
notifications. notifications.
4.3. Mitigation option 4.3. Mitigation Option
It is important to note that this attack is not based on a weakness It is important to note that this attack is not based on a weakness
of the protocol but on the ignorance of the upper layer. This attack of the protocol, but on the ignorance of the upper layer. This
is not possible if the upper layer processes the restart attack is not possible if the upper layer processes the restart
notifications provided by SCTP as described in section 10 of notifications provided by SCTP as described in section 10 of
[RFC2960] or [I-D.ietf-tsvwg-2960bis]. Note that other IP protocols [RFC2960] or [RFC4960]. Note that other IP protocols may also be
may also be effected by this attack. affected by this attack.
5. Bombing attack (amplification) 1 5. Bombing Attack (Amplification) 1
The bombing attack is a method to get a server to amplify packets to The bombing attack is a method to get a server to amplify packets to
an innocent victim. an innocent victim.
5.1. Attack details 5.1. Attack Details
This attack is performed by setting up an association with a peer and This attack is performed by setting up an association with a peer and
listing the victims IP address in the INIT's list of addresses. listing the victims IP address in the INIT's list of addresses.
After the association is setup, the attacker makes a request for a After the association is setup, the attacker makes a request for a
large data transfer. After making the request the attacker does not large data transfer. After making the request, the attacker does not
acknowledge data sent to it. This then causes the server to re- acknowledge data sent to it. This then causes the server to re-
transmit the data to the alternate address i.e. that of the victim. transmit the data to the alternate address, i.e., that of the victim.
After waiting an appropriate time period the attacker acknowledges
the data for the victim. At some point the attackers address is After waiting an appropriate time period, the attacker acknowledges
the data for the victim. At some point, the attackers address is
considered unreachable since only data sent to the victims address is considered unreachable since only data sent to the victims address is
acknowledged. At this point the attacker can send strategic acknowledged. At this point, the attacker can send strategic
acknowledgments so that the server continues to send data to the acknowledgments so that the server continues to send data to the
victim. victim.
Alternatively, instead of stopping the sending of SACKs to enforce a Alternatively, instead of stopping the sending of SACKs to enforce a
path failover, the attacker can use the ADD-IP extension to add the path failover, the attacker can use the ADD-IP extension to add the
address of the victim and make that address the primary path. address of the victim and make that address the primary path.
5.2. Analysis 5.2. Analysis
This attack depends on a number of circumstances: This attack depends on a number of circumstances:
1) The victim must NOT support SCTP, otherwise it would respond with 1) The victim must NOT support SCTP, otherwise it would respond with
an OOTB abort. an "out of the blue" (OOTB) abort.
2) The attacker must time its sending of acknowledgments correctly in 2) The attacker must time its sending of acknowledgments correctly in
order to get its address into the failed state and the victims order to get its address into the failed state and the victim's
address as the only valid alternative. address as the only valid alternative.
3) The attacker must guess TSN values that are accepted by the 3) The attacker must guess TSN values that are accepted by the
receiver once the bombing begins since it must acknowledge packets receiver once the bombing begins since it must acknowledge packets
it no longer is seeing. it is no longer seeing.
5.3. Mitigation option 5.3. Mitigation Option
[I-D.ietf-tsvwg-2960bis] makes two changes to prevent this attack. [RFC4960] makes two changes to prevent this attack. First, it
First it details out proper handling of ICMP messages. With SCTP the details proper handling of ICMP messages. With SCTP, the ICMP
ICMP messages provide valuable clues to the SCTP stack that can be messages provide valuable clues to the SCTP stack that can be
verified with the tags for authenticity. Proper handling of an ICMP verified with the tags for authenticity. Proper handling of an ICMP
protocol unreachable (or equivalent) would cause the association protocol unreachable (or equivalent) would cause the association
setup by the attacker to be immediately failed upon the first setup by the attacker to be immediately failed upon the first
retransmission to the victims address. retransmission to the victim's address.
The second change made in [I-D.ietf-tsvwg-2960bis] is the requirement The second change made in [RFC4960] is the requirement that no
that no address that is not CONFIRMED is allowed to have DATA chunks address that is not CONFIRMED is allowed to have DATA chunks sent to
sent to it. This prevents the switch-over to the alternate address it. This prevents the switch-over to the alternate address from
from occurring even when ICMP messages are lost in the network and occurring, even when ICMP messages are lost in the network and
prevents any DATA chunks from being sent to any other destination prevents any DATA chunks from being sent to any other destination
other then the attacker itself. This also prevents the alternative other then the attacker itself. This also prevents the alternative
way of using ADD-IP to add the new address and make it the primary way of using ADD-IP to add the new address and make it the primary
address. address.
An SCTP implementation should abort the association if it receives a An SCTP implementation should abort the association if it receives a
SACK acknowledging a TSN which has not been sent. This makes TSN SACK acknowledging a TSN that has not been sent. This makes TSN
guessing for the attacker quite hard because if the attacker guessing for the attacker quite hard because if the attacker
acknowledges one TSN too fast the association will be aborted. acknowledges one TSN too fast, the association will be aborted.
6. Bombing attack (amplification) 2 6. Bombing Attack (Amplification) 2
This attack allows an attacker to use an arbitrary SCTP endpoint to This attack allows an attacker to use an arbitrary SCTP endpoint to
send multiple packets to a victim in response to one packet. send multiple packets to a victim in response to one packet.
6.1. Attack details 6.1. Attack Details
The attacker sends an INIT listing multiple IP addresses of the The attacker sends an INIT listing multiple IP addresses of the
victim in the INIT's list of addresses to an arbitrary endpoint. victim in the INIT's list of addresses to an arbitrary endpoint.
Optionally it request a long cookie life time. Upon reception of the Optionally, it requests a long cookie lifetime. Upon reception of
INIT-ACK it stores the cookie and sends it back to the other the INIT-ACK, it stores the cookie and sends it back to the other
endpoint. When the other endpoint receives the COOKIE it will send endpoint. When the other endpoint receives the COOKIE, it will send
back a COOKIE-ACK to the attacker and up to HB.Max.Burst HEARTBEATS back a COOKIE-ACK to the attacker and up to HB.Max.Burst HEARTBEATS
to the victim's address(es) (to confirm these addresses). The victim to the victim's address(es) (to confirm these addresses). The victim
responds with ABORTs or ICMP messages resulting in the removal of the responds with ABORTs or ICMP messages resulting in the removal of the
TCB at the other endpoint. The attacker can now resend the stored TCB at the other endpoint. The attacker can now resend the stored
cookie as long as it is valid and this will again result in up to cookie as long as it is valid, and this will again result in up to
HB.Max.Burst HEARTBEATs sent to the victim('s). HB.Max.Burst HEARTBEATs sent to the victim('s).
6.2. Analysis 6.2. Analysis
The multiplication factor is limited by the number of addresses of The multiplication factor is limited by the number of addresses of
the victim and of the end point HB.Max.Burst. Also the shorter the the victim and of the endpoint HB.Max.Burst. Also, the shorter the
cookie life time is, the earlier the attacker has to go through the cookie lifetime, the earlier the attacker has to go through the
initial stage of sending an INIT instead of the just sending the initial stage of sending an INIT instead of just sending the COOKIE.
COOKIE. It should also be noted that the attack is more effective if It should also be noted that the attack is more effective if large
large HEARTBEATs are used for path confirmation. HEARTBEATs are used for path confirmation.
6.3. Mitigation option 6.3. Mitigation Option
To limit the effectiveness of this attack the new parameter To limit the effectiveness of this attack, the new parameter
HB.Max.Burst was introduced in [I-D.ietf-tsvwg-2960bis] and an end HB.Max.Burst was introduced in [RFC4960] and an endpoint should:
point should:
1) not allow very large cookie lifetimes, even if they are requested. 1) not allow very large cookie lifetimes, even if they are requested.
2) not use larger HB.Max.Burst parameter values than recommended. 2) not use larger HB.Max.Burst parameter values than recommended.
Note that an endpoint may decide to send only one Heartbeat per Note that an endpoint may decide to send only one Heartbeat per
RTT instead of the maximum (i.e. HB.Max.Burst). An endpoint that RTT instead of the maximum (i.e., HB.Max.Burst). An endpoint that
chooses this approach will however slow down detection of chooses this approach will however slow down detection of
endpoints camping on valid addresses. endpoints camping on valid addresses.
3) not use large HEARTBEATs for path confirmation. 3) not use large HEARTBEATs for path confirmation.
7. Association redirection 7. Association Redirection
This attack allows an attacker to wrongly setup an association to a This attack allows an attacker to wrongly setup an association to a
different endpoint. different endpoint.
7.1. Attack details 7.1. Attack Details
The attacker sends an INIT sourced from port 'X' and directed towards The attacker sends an INIT sourced from port 'X' and directed towards
port 'Y'. When the INIT-ACK is returned the attacker sends the port 'Y'. When the INIT-ACK is returned, the attacker sends the
COOKIE-ECHO chunk and either places a different destination or source COOKIE-ECHO chunk and either places a different destination or source
port in the SCTP common header, i.e., X+1 or Y+1. This then sets up port in the SCTP common header, i.e., X+1 or Y+1. This possibly sets
the association with possibly other endpoints. up the association using the modified port numbers.
7.2. Analysis 7.2. Analysis
This attack depends on the failure of an SCTP implementation to store This attack depends on the failure of an SCTP implementation to store
and verify the ports within the COOKIE structure. and verify the ports within the COOKIE structure.
7.3. Mitigation option 7.3. Mitigation Option
This attack is easily defeated by an implementation including the This attack is easily defeated by an implementation including the
ports of both the source and destination within the COOKIE. When the ports of both the source and destination within the COOKIE. If the
COOKIE is returned if the source and destination ports do not match source and destination ports do not match those within the COOKIE
those within the COOKIE chunk, the SCTP implementation silently chunk when the COOKIE is returned, the SCTP implementation silently
discards the invalid COOKIE. discards the invalid COOKIE.
8. Bombing attack (amplification) 3 8. Bombing Attack (Amplification) 3
This attack allows an attacker to use an SCTP endpoint to send a This attack allows an attacker to use an SCTP endpoint to send a
large number of packets in response to one packet. large number of packets in response to one packet.
8.1. Attack details 8.1. Attack Details
The attacker sends a packet to an SCTP endpoint which requires the The attacker sends a packet to an SCTP endpoint, which requires the
sending of multiple chunks. If the SCTP endpoint does not support sending of multiple chunks. If the SCTP endpoint does not support
bundling on the sending side it might send each chunk per packet. bundling on the sending side, it might send each chunk per packet.
These packets can either be sent to a victim by using the victim's These packets can either be sent to a victim by using the victim's
address as the sources address or it can be considered an attack address as the sources address, or it can be considered an attack
against the network. Since the chunks which need to be send in against the network. Since the chunks, which need to be sent in
response to the received packet may not fit into one packet an response to the received packet, may not fit into one packet, an
endpoint supporting bundling on the sending side might send multiple endpoint supporting bundling on the sending side might send multiple
packets. packets.
Examples of these packets are packets containing a lot of unknown Examples of these packets are packets containing a lot of unknown
chunks which require an ERROR chunk to be sent, known chunks which chunks that require an ERROR chunk to be sent, known chunks that
initiate the sending of ERROR chunks, packets containing a lot of initiate the sending of ERROR chunks, packets containing a lot of
HEARTBEAT chunks and so on. HEARTBEAT chunks, and so on.
8.2. Analysis 8.2. Analysis
This attack depends on the fact that the SCTP endpoint does not This attack depends on the fact that the SCTP endpoint does not
support bundling on the sending side or provides a bad implementation support bundling on the sending side or provides a bad implementation
of bundling on the sending side. of bundling on the sending side.
8.3. Mitigation option 8.3. Mitigation Option
First of all, path verification must happen before sending other First of all, path verification must happen before sending chunks
chunks than HEARTBEATs for path verification. This makes sure that other than HEARTBEATs for path verification. This ensures that the
the above attack can not be used against other hosts. To avoid the above attack cannot be used against other hosts. To avoid the
attack, an SCTP endpoint should implement bundling on the sending attack, an SCTP endpoint should implement bundling on the sending
side and should not send multiple packets in response. If the SCTP side and should not send multiple packets in response. If the SCTP
endpoint does not support bundling on the sending side it should not endpoint does not support bundling on the sending side, it should not
send in general more than one packet in response to a received one. send in general more than one packet in response to a received one.
The details of the required handling are described in the The details of the required handling are described in [RFC4960].
[I-D.ietf-tsvwg-2960bis].
9. Bombing attack (amplification) 4 9. Bombing Attack (Amplification) 4
This attack allows an attacker to use an SCTP server to send a larger This attack allows an attacker to use an SCTP server to send a larger
packets to a victim than it sent to the SCTP server. packet to a victim than it sent to the SCTP server.
9.1. Attack details 9.1. Attack Details
The attacker sends packets using the victim's address as the source The attacker sends packets using the victim's address as the source
address containing an INIT chunk to an SCTP Server. The server then address containing an INIT chunk to an SCTP Server. The server then
sends an packet containing an INIT-ACK chunk to the victim, which is sends a packet containing an INIT-ACK chunk to the victim, which is
most likely larger than the packet containing the INIT. most likely larger than the packet containing the INIT.
9.2. Analysis 9.2. Analysis
This attack is a byte and not a packet amplification attack and This attack is a byte and not a packet amplification attack and,
without protocol changes hard to avoid. A possible method would be without protocol changes, is hard to avoid. A possible method to
the usage of the PAD parameter defined in [RFC4820]. avoid this attack would be the usage the PAD parameter defined in
[RFC4820].
9.3. Mitigation option 9.3. Mitigation Option
A server should be implemented in a way that the generated INIT-ACK A server should be implemented in a way that the generated INIT-ACK
chunks are as small as possible. chunks are as small as possible.
10. Bombing attack (amplification) 5 10. Bombing Attack (amplification) 5
This attack allows an attacker to use an SCTP endpoint to send a This attack allows an attacker to use an SCTP endpoint to send a
large number of packets in response to one packet. large number of packets in response to one packet.
10.1. Attack details 10.1. Attack Details
The attacker sends a packet to an SCTP endpoint which requires the The attacker sends a packet to an SCTP endpoint, which requires the
sending of multiple chunks. If the MTU towards the attacker is sending of multiple chunks. If the MTU towards the attacker is
smaller than the MTU towards the victim, the victim might need to smaller than the MTU towards the victim, the victim might need to
send more than one packet to send all the chunks. The difference send more than one packet to send all the chunks. The difference
between the MTUs might be extremely large if the attacker sends between the MTUs might be extremely large if the attacker sends
malicious ICMP packets to make use of the path MTU discovery. malicious ICMP packets to make use of the path MTU discovery.
10.2. Analysis 10.2. Analysis
This attack depends on the fact that an SCTP implementation might not This attack depends on the fact that an SCTP implementation might not
not limit the number of response packets correctly. limit the number of response packets correctly.
10.3. Mitigation option 10.3. Mitigation Option
First of all, path verification must happen before sending other First of all, path verification must happen before sending chunks
chunks than HEARTBEATs for path verification. This makes sure that other than HEARTBEATs for path verification. This makes sure that
the above attack can not be used against other hosts. To avoid the the above attack can not be used against other hosts. To avoid the
attack, an SCTP endpoint should not send multiple packets in response attack, an SCTP endpoint should not send multiple packets in response
to a single packet. The chunks not fitting in this packet should be to a single packet. The chunks not fitting in this packet should be
dropped. dropped.
11. Security Considerations 11. Security Considerations
This document is about security and there is nothing to be added to This document is about security; as such, there are no additional
it in this section. security considerations.
12. IANA considerations
There are no actions required from IANA.
13. References 12. References
13.1. Normative References 12.1. Normative References
[RFC2960] Stewart, R., Xie, Q., Morneault, K., Sharp, C., [RFC2960] Stewart, R., Xie, Q., Morneault, K., Sharp, C.,
Schwarzbauer, H., Taylor, T., Rytina, I., Kalla, M., Schwarzbauer, H., Taylor, T., Rytina, I., Kalla, M.,
Zhang, L., and V. Paxson, "Stream Control Transmission Zhang, L., and V. Paxson, "Stream Control Transmission
Protocol", RFC 2960, October 2000. Protocol", RFC 2960, October 2000.
[RFC4460] Stewart, R., Arias-Rodriguez, I., Poon, K., Caro, A., and [RFC4460] Stewart, R., Arias-Rodriguez, I., Poon, K., Caro, A., and
M. Tuexen, "Stream Control Transmission Protocol (SCTP) M. Tuexen, "Stream Control Transmission Protocol (SCTP)
Specification Errata and Issues", RFC 4460, April 2006. Specification Errata and Issues", RFC 4460, April 2006.
[I-D.ietf-tsvwg-2960bis]
Stewart, R., "Stream Control Transmission Protocol",
draft-ietf-tsvwg-2960bis-05 (work in progress), June 2007.
[RFC4820] Tuexen, M., Stewart, R., and P. Lei, "Padding Chunk and [RFC4820] Tuexen, M., Stewart, R., and P. Lei, "Padding Chunk and
Parameter for the Stream Control Transmission Protocol Parameter for the Stream Control Transmission Protocol
(SCTP)", RFC 4820, March 2007. (SCTP)", RFC 4820, March 2007.
[I-D.ietf-tsvwg-sctp-auth] [RFC4895] Tuexen, M., Stewart, R., Lei, P., and E. Rescorla,
Tuexen, M., "Authenticated Chunks for Stream Control "Authenticated Chunks for Stream Control Transmission
Transmission Protocol (SCTP)", Protocol (SCTP)", RFC 4895, August 2007.
draft-ietf-tsvwg-sctp-auth-08 (work in progress),
February 2007.
[I-D.ietf-tsvwg-addip-sctp] [RFC5061] Stewart, R., Xie, Q., Tuexen, M., Maruyama, S., and M.
Stewart, R., "Stream Control Transmission Protocol (SCTP) Kozuka, "Stream Control Transmission Protocol (SCTP)
Dynamic Address Reconfiguration", Dynamic Address Reconfiguration", RFC 5061,
draft-ietf-tsvwg-addip-sctp-21 (work in progress), September 2007.
June 2007.
13.2. Informative References [RFC4960] Stewart, R., Ed., "Stream Control Transmission Protocol",
RFC 4960, June 2007.
[effects] Aura, T., Nikander, P., and G. Camarillo, "Effects of 12.2. Informative References
[EFFECTS] Aura, T., Nikander, P., and G. Camarillo, "Effects of
Mobility and Multihoming on Transport-Layer Security", Mobility and Multihoming on Transport-Layer Security",
Security and Privacy 2004, IEEE Symposium , URL http:// Security and Privacy 2004, IEEE Symposium , URL http://
research.microsoft.com/users/tuomaura/Publications/ research.microsoft.com/users/tuomaura/Publications/
aura-nikander-camarillo-ssp04.pdf, May 2004. aura-nikander-camarillo-ssp04.pdf, May 2004.
Authors' Addresses Authors' Addresses
Randall R. Stewart Randall R. Stewart
Cisco Systems, Inc. Cisco Systems, Inc.
4785 Forest Drive 4785 Forest Drive
Suite 200 Suite 200
Columbia, SC 29206 Columbia, SC 29206
USA USA
Email: rrs@cisco.com EMail: rrs@cisco.com
Michael Tuexen Michael Tuexen
Muenster Univ. of Applied Sciences Muenster Univ. of Applied Sciences
Stegerwaldstr. 39 Stegerwaldstr. 39
48565 Steinfurt 48565 Steinfurt
Germany Germany
Email: tuexen@fh-muenster.de EMail: tuexen@fh-muenster.de
Gonzalo Camarillo Gonzalo Camarillo
Ericsson Ericsson
Hirsalantie 11 Hirsalantie 11
Jorvas 02420 Jorvas 02420
Finland Finland
Email: Gonzalo.Camarillo@ericsson.com EMail: Gonzalo.Camarillo@ericsson.com
Full Copyright Statement Full Copyright Statement
Copyright (C) The IETF Trust (2007). Copyright (C) The IETF Trust (2007).
This document is subject to the rights, licenses and restrictions This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors contained in BCP 78, and except as set forth therein, the authors
retain all their rights. retain all their rights.
This document and the information contained herein are provided on an This document and the information contained herein are provided on an
skipping to change at page 16, line 44 skipping to change at line 623
attempt made to obtain a general license or permission for the use of attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr. http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at this standard. Please address the information to the IETF at
ietf-ipr@ietf.org. ietf-ipr@ietf.org.
Acknowledgment
Funding for the RFC Editor function is provided by the IETF
Administrative Support Activity (IASA).
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