wdiff rfc5062.original rfc5062.txt

Network Working Group R. Stewart
Internet-Draft
Request for Comments: 5062 Cisco Systems, Inc.
Expires: December 15, 2007
Category: Informational M. Tuexen
Muenster Univ. of Applied Sciences
G. Camarillo
Ericsson
June 13,
September 2007

Security Attacks Found Against SCTP Stream Control Transmission Protocol
(SCTP) and Current Countermeasures
draft-ietf-tsvwg-sctpthreat-05.txt

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Abstract

This document describes certain security threats to SCTP. It also
describes ways to mitigate these threats, in particular by using
techniques from the SCTP Specification Errata and Issues memo (RFC
4460). These techniques are included in RFC 4960, which obsoletes
RFC 2960. It is hoped that this information will provide some useful
background information for many of the newest requirements spelled
out in the SCTP Specification Errata and Issues and included in RFC
4960.

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Address Camping or stealing Stealing . . . . . . . . . . . . . . . . . 3
3. Association hijacking Hijacking 1 . . . . . . . . . . . . . . . . . . . 5
4. Association hijacking Hijacking 2 . . . . . . . . . . . . . . . . . . . 7
5. Bombing attack (amplification) Attack (Amplification) 1 . . . . . . . . . . . . . . . 8
6. Bombing attack (amplification) 2 Attack Details . . . . . . . . . . . . . . . . . . . 10
7. Association redirection . . . . . 8
7. Bombing Attack (Amplification) 2 . . . . . . . . . . . . . . 11 . 9
8. Bombing attack (amplification) 3 Association Redirection . . . . . . . . . . . . . . . 11 . . . . 10
9. Bombing attack (amplification) 4 Attack (Amplification) 3 . . . . . . . . . . . . . . . 12 11
10. Bombing attack (amplification) 5 Attack (Amplification) 4 . . . . . . . . . . . . . . . 12
11. Security Considerations . . . . Bombing Attack (amplification) 5 . . . . . . . . . . . . . . . 13 12
12. IANA considerations . . Security Considerations . . . . . . . . . . . . . . . . . . . 13
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
13.1. Normative References . . . . . . . . . . . . . . . . . . 13
13.2. Informative References . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14
Intellectual Property and Copyright Statements . . . . . . . . . . 16 13

1. Introduction

Stream Control Transmission Protocol Protocol, originally defined in [RFC2960]
[RFC2960], is a multi-homed transport protocol. As such, unique
security threats exists that are addressed in various ways within the
protocol itself. This document describes certain security threats to
SCTP. It also describes ways to mitigate these threats, in
particular by using techniques from the SCTP Specification Errata and
Issues memo
([RFC4460]). [RFC4460]. These techniques are included in
[I-D.ietf-tsvwg-2960bis], [RFC4960],
which obsoletes [RFC2960]. It is hoped that this information will
provide some useful background information for many of the newest
requirements spelled out in the [RFC4460] and included in [I-D.ietf-tsvwg-2960bis]. [RFC4960].

This work and some of the changes that went into the [RFC4460] and
[I-D.ietf-tsvwg-2960bis]
[RFC4960] are much indebted to the paper on potential SCTP security
risks Effects [effects] [EFFECTS] by Aura, Nikander Nikander, and Camarillo. Without their work
work, some of these changes would remain undocumented and potential
threats.

The rest of this document will concentrate on the various attacks
that were illustrated in Effects [effects] and [EFFECTS]and detail what the preventative
measures are now in place place, if any, within the current SCTP
standards (if any). standards.

2. Address Camping or stealing Stealing

This attack is a form of denial of service attack crafted around
SCTP's multi-homing. In effect effect, an illegitimate endpoint connects to
a server and "camps upon" or holds up "holds up" a valid peers peer's address. This
is done to prevent the legitimate peer from communicating with the
server.

2.1. Attack details Details

Figure 1: Camping

Consider the scenario illustrated in Figure 1. The attacker
legitimately holds IP-A and wishes to prevent the 'Client-Victim'
from communication communicating with the 'Server'. Note also that the client is
multi-homed. The attacker first guesses the port number our client
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
as well
in its initial INIT chunk. The server will respond and setup set up the association
association, noting that the attacker is multi-homed holding and holds both
IP-A and IP-C.

Next, the victim sends in an INIT message listing its two valid
addresses
addresses, IP-C and IP-D. In response response, it will receive an ABORT
message with possibly an error code indicating that a new address was
added in its attempt to setup set up an existing association (a restart
with new addresses). At this point point, 'Client-Victim' is now prevented
from setting up an association with the server until the server
realizes that the attacker does not hold the address IP-C at some
future point by using a HEARTBEAT based mechanism. See the
mitigation option subsection of this section.

2.2. Analysis

This particular attack was discussed in detail on the SCTP
implementors list in March of 2003. Out of that discussion discussion, changes
were made in the BSD implementation that are now present in the
[I-D.ietf-tsvwg-2960bis].
[RFC4960]. In close examination, this attack depends on a number of
specific things to occur.

1) The attacker must setup set up the association before the victim and
must correctly guess the port number that the victim will use. If
the victim uses any other port number the attack will fail.

2) SCTP's existing HEARTBEAT mechanism as defined already in
[RFC2960] will eventually catch this situation and abort the evil
attackers
attacker's association. This may take several seconds based on
default HEARTBEAT timers but the attacker himself will lose any
association.

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
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 and the server while destroying the association between the
attacker and the server. From the servers' perspective perspective, this is a
restart of the association.

2.3. Mitigation option

[I-D.ietf-tsvwg-2960bis] Option

[RFC4960] adds a new set of requirements to better counter this
attack. In particular particular, the HEARTBEAT mechanism was modified so that
addresses unknown to an endpoint (i.e. (i.e., presented in an INIT with no
pre-knowledge given by the application) enter a new state called
"UNCONFIRMED". During the time that any address is UNCONFIRMED and
yet considered available, heartbeating will be done on those
UNCONFIRMED addresses at an accelerated rate. This will lessen the
time that an attacker can "camp" on an address. In
particular particular, the
rate of heartbeats to UNCONFIRMED addresses is done every RTO. Along
with this expanded rate of heartbeating, a new 64
bit 64-bit random nonce is
required to be inside HEARTBEATs to UNCONFIRMED addresses. In the HEARTBEAT-ACK
HEARTBEAT-ACK, the random nonce must match the value sent in the
HEARTBEAT before an address can leave the UNCONFIRMED state. This
will prevent an attacker from generating false HEARTBEAT-ACKs with
the victims victim's source address(es). In addition, clients which that do not
need to use a specific port number should choose their port numbers
on a random base. basis. This makes it hard for an attacker to guess that
number.

3. Association hijacking Hijacking 1

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-
middle
middle, only a strong end-to-end security model can prevent this.
However
However, with the addition of the [I-D.ietf-tsvwg-addip-sctp]
extension to SCTP extension specified in
[RFC5061], an endpoint that is NOT a man-in-the-middle may be able to
assume another endpoints endpoint's association.

3.1. Attack details Details

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
endpoint. For example in a mobile network SCTP
endpoint. For example, DHCP may be used in use a mobile network with
short IP address lifetimes to reassign IP addresses to migrant hosts.

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
the new address and delete to old address at point 2, but this packet
is lost. Thus Thus, our peer (Peer-Server) has no idea that the former
peer is no longer at IP-A. Now at point 3 3, a new "evil" peer DHCP's obtains
an address via DHCP and it happens to get the re-assigned address
IP-A. Our Peer-Server sends a chunk of DATA at point 4. This
reveals to the new owner of IP-A that the former owner of IP-A had an
association with Peer-Server. So at point 5 5, the new owner of IP-A
sends an INIT. The INIT-ACK is sent back and inside it is a COOKIE.
The cookie would of course hold tie-tags tie-tags, which would list both sets
of tags
which that could then be used at point 6 to add in any other IP
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
the attacker is able to send packets with source address IP-A and
receive packets with destination address IP-A.

3.2. Analysis

This attack depends on a number of events:

1) Both endpoints must support the [I-D.ietf-tsvwg-addip-sctp]
extension. SCTP extension specified in
[RFC5061].

2) One of the endpoints must be using the [I-D.ietf-tsvwg-addip-sctp] SCTP extension for mobility. mobility
specified in [RFC5061].

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
concerned.

4) The true peer must not get receive the ASCONF packet that deletes IP-A
and adds its new address to the peer before the new "evil" peer
gets control of the association.

5) The new "evil" peer must have an alternative address besides alternate address, aside from the
IP-A that it can add to the association association, so it can delete IP-A IP-A,
preventing the real peer from re-acquiring the association when it
finally retransmits the ASCONF (from step 2).

3.3. Mitigation option

[I-D.ietf-tsvwg-2960bis] Option

[RFC4960] adds a new counter measure to this threat. It is now
required that Tie-Tags in the State-Cookie parameter not be the
actual tags. Instead Instead, a new pair of two 32 bit 32-bit nonces must be used
to represent the real tags within the association. This prevents the
attacker from acquiring the real tags and thus prevents this attack. Furthermore
Furthermore, the use of the [I-D.ietf-tsvwg-addip-sctp]
extensions SCTP extension specified in [RFC5061]
requires the use of the authentication mechanism defined in [I-D.ietf-tsvwg-sctp-auth].
[RFC4895]. This requires the attacker to be able to capture the
traffic during the association setup. If in addition an end-point endpoint-
pair shared key is used, capturing or intercepting these setup
messages does not enable the attacker to hijack the association.

4. Association hijacking Hijacking 2

Association hijacking is the ability of some other user to assume the
session created by another endpoint. In cases where an attacker can
send packets using the victims IP-address as a source address and can
receive packets with the victims' address as a destination address address,
the attacker can easily restart the association. If the peer does
not pay attention to the restart notification notification, the attacker has taken
over the association.

4.1. Attack details Details

Assume that an endpoint E1 having an IP-address A has an SCTP
association with endpoint E2. After the attacker is able to receive
packets with to destination address A and send packet packets with source address A
A, the attacker can perform a full four-way handshake using the the IP-addresses IP-
addresses and port numbers from the received packet. E2 will
consider this as a restart of the association. If and only if the SCTP
user of E2 does not process the restart notification notification, the user will
not recognize that that the association just restarted. From
his perspective this
perspective, the association has been hijacked.

4.2. Analysis

This attack depends on a number of circumstances:

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
local LAN is concerned.

2) The attacker must receive a packet belonging to the association or
connection.

3) The other endpoints endpoint's user does not pay attention to restart
notifications.

4.3. Mitigation option Option

It is important to note that this attack is not based on a weakness
of the protocol protocol, but on the ignorance of the upper layer. This
attack is not possible if the upper layer processes the restart
notifications provided by SCTP as described in section 10 of
[RFC2960] or [I-D.ietf-tsvwg-2960bis]. [RFC4960]. Note that other IP protocols may also be effected
affected by this attack.

5. Bombing attack (amplification) Attack (Amplification) 1

The bombing attack is a method to get a server to amplify packets to
an innocent victim.

5.1.

6. Attack details Details

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.
After the association is setup, the attacker makes a request for a
large data transfer. After making the request request, the attacker does not
acknowledge data sent to it. This then causes the server to re-
transmit the data to the alternate address i.e. address, i.e., that of the victim.
After waiting an appropriate time period period, the attacker acknowledges
the data for the victim. At some point point, the attackers address is
considered unreachable since only data sent to the victims address is
acknowledged. At this point point, the attacker can send strategic
acknowledgments so that the server continues to send data to the
victim.

Alternatively, instead of stopping the sending of SACKs to enforce a
path failover, the attacker can use the ADD-IP extension to add the
address of the victim and make that address the primary path.

5.2.

6.1. Analysis

This attack depends on a number of circumstances:

1) The victim must NOT support SCTP, otherwise it would respond with
an OOTB "out of the blue" (OOTB) abort.

2) The attacker must time its sending of acknowledgments correctly in
order to get its address into the failed state and the victims victim's
address as the only valid alternative.

3) The attacker must guess TSN values that are accepted by the
receiver once the bombing begins since it must acknowledge packets
it is no longer is seeing.

5.3.

6.2. Mitigation option

[I-D.ietf-tsvwg-2960bis] Option

[RFC4960] makes two changes to prevent this attack.
First First, it
details out proper handling of ICMP messages. With SCTP SCTP, the ICMP
messages provide valuable clues to the SCTP stack that can be
verified with the tags for authenticity. Proper handling of an ICMP
protocol unreachable (or equivalent) would cause the association
setup by the attacker to be immediately failed upon the first
retransmission to the victims victim's address.

The second change made in [I-D.ietf-tsvwg-2960bis] [RFC4960] is the requirement that no
address that is not CONFIRMED is allowed to have DATA chunks sent to
it. This prevents the switch-over to the alternate address from occurring
occurring, even when ICMP messages are lost in the network and
prevents any DATA chunks from being sent to any other destination
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
address.

An SCTP implementation should abort the association if it receives a
SACK acknowledging a TSN which that has not been sent. This makes TSN
guessing for the attacker quite hard because if the attacker
acknowledges one TSN too fast fast, the association will be aborted.

7. Bombing attack (amplification) Attack (Amplification) 2

This attack allows an attacker to use an arbitrary SCTP endpoint to
send multiple packets to a victim in response to one packet.

6.1.

7.1. Attack details Details

The attacker sends an INIT listing multiple IP addresses of the
victim in the INIT's list of addresses to an arbitrary endpoint.
Optionally
Optionally, it request requests a long cookie life time. lifetime. Upon reception of
the
INIT-ACK INIT-ACK, it stores the cookie and sends it back to the other
endpoint. When the other endpoint receives the COOKIE COOKIE, it will send
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
responds with ABORTs or ICMP messages resulting in the removal of the
TCB at the other endpoint. The attacker can now resend the stored
cookie as long as it is valid valid, and this will again result in up to
HB.Max.Burst HEARTBEATs sent to the victim('s).

6.2.

7.2. Analysis

The multiplication factor is limited by the number of addresses of
the victim and of the end point endpoint HB.Max.Burst. Also Also, the shorter the
cookie life time is, lifetime, the earlier the attacker has to go through the
initial stage of sending an INIT instead of the just sending the COOKIE.
It should also be noted that the attack is more effective if large
HEARTBEATs are used for path confirmation.

6.3.

7.3. Mitigation option Option

To limit the effectiveness of this attack attack, the new parameter
HB.Max.Burst was introduced in [I-D.ietf-tsvwg-2960bis] [RFC4960] and an end
point endpoint should:

1) not allow very large cookie lifetimes, even if they are requested.

2) not use larger HB.Max.Burst parameter values than recommended.
Note that an endpoint may decide to send only one Heartbeat per
RTT instead of the maximum (i.e. (i.e., HB.Max.Burst). An endpoint that
chooses this approach will however slow down detection of
endpoints camping on valid addresses.

3) not use large HEARTBEATs for path confirmation.

8. Association redirection Redirection

This attack allows an attacker to wrongly setup set up an association to a
different endpoint.

7.1.

8.1. Attack details Details

The attacker sends an INIT sourced from port 'X' and directed towards
port 'Y'. When the INIT-ACK is returned returned, the attacker sends the
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
the possible association with possibly other endpoints.

7.2.

8.2. Analysis

This attack depends on the failure of an SCTP implementation to store
and verify the ports within the COOKIE structure.

7.3.

8.3. Mitigation option Option

This attack is easily defeated by an implementation including the
ports of both the source and destination within the COOKIE. When the
COOKIE is returned if If the
source and destination ports do not match those within the COOKIE chunk,
chunk when the COOKIE is returned, the SCTP implementation silently
discards the invalid COOKIE.

9. Bombing attack (amplification) Attack (Amplification) 3

This attack allows an attacker to use an SCTP endpoint to send a
large number of packets in response to one packet.

8.1.

9.1. Attack details Details

The attacker sends a packet to an SCTP endpoint endpoint, which requires the
sending of multiple chunks. If the SCTP endpoint does not support
bundling on the sending side side, it might send each chunk per packet.
These packets can either be sent to a victim by using the victim's
address as the sources address address, or it can be considered an attack
against the network. Since the chunks chunks, which need to be send sent in
response to the received packet packet, may not fit into one packet packet, an
endpoint supporting bundling on the sending side might send multiple
packets.

Examples of these packets are packets containing a lot of unknown
chunks which that require an ERROR chunk to be sent, known chunks which that
initiate the sending of ERROR chunks, packets containing a lot of
HEARTBEAT chunks chunks, and so on.

8.2.

9.2. Analysis

This attack depends on the fact that the SCTP endpoint does not
support bundling on the sending side or provides a bad implementation
of bundling on the sending side.

8.3.

9.3. Mitigation option Option

First of all, path verification must happen before sending other chunks
other than HEARTBEATs for path verification. This makes sure ensures that the
above attack can not cannot be used against other hosts. To avoid the
attack, an SCTP endpoint should implement bundling on the sending
side and should not send multiple packets in response. If the SCTP
endpoint does not support bundling on the sending side side, it should not
send in general more than one packet in response to a received one.
The details of the required handling are described in the
[I-D.ietf-tsvwg-2960bis].

9. [RFC4960].

10. Bombing attack (amplification) Attack (Amplification) 4

This attack allows an attacker to use an SCTP server to send a larger
packets
packet to a victim than it sent to the SCTP server.

9.1.

10.1. Attack details Details

The attacker sends packets using the victim's address as the source
address containing an INIT chunk to an SCTP Server. The server then
sends an a packet containing an INIT-ACK chunk to the victim, which is
most likely larger than the packet containing the INIT.

9.2.

10.2. Analysis

This attack is a byte and not a packet amplification attack and and,
without protocol changes changes, is hard to avoid. A possible method to
avoid this attack would be the usage of the PAD parameter defined in
[RFC4820].

9.3.

10.3. Mitigation option Option

A server should be implemented in a way that the generated INIT-ACK
chunks are as small as possible.

10.

11. Bombing attack Attack (amplification) 5

This attack allows an attacker to use an SCTP endpoint to send a
large number of packets in response to one packet.

10.1.

11.1. Attack details Details

The attacker sends a packet to an SCTP endpoint endpoint, which requires the
sending of multiple chunks. If the MTU towards the attacker is
smaller than the MTU towards the victim, the victim might need to
send more than one packet to send all the chunks. The difference
between the MTUs might be extremely large if the attacker sends
malicious ICMP packets to make use of the path MTU discovery.

10.2.

11.2. Analysis

This attack depends on the fact that an SCTP implementation might not
not
limit the number of response packets correctly.

10.3.

11.3. Mitigation option Option

First of all, path verification must happen before sending other chunks
other than HEARTBEATs for path verification. This makes sure that
the above attack can not cannot be used against other hosts. To avoid the
attack, an SCTP endpoint should not send multiple packets in response
to a single packet. The chunks not fitting in this packet should be
dropped.

11.

12. Security Considerations

This document is about security and security; as such, there is nothing to be added to
it in this section.

12. IANA considerations

There are no actions required from IANA. additional
security considerations.

13. References

13.1. Normative References

[RFC2960] Stewart, R., Xie, Q., Morneault, K., Sharp, C.,
Schwarzbauer, H., Taylor, T., Rytina, I., Kalla, M.,
Zhang, L., and V. Paxson, "Stream Control Transmission
Protocol", RFC 2960, October 2000.

[RFC4460] Stewart, R., Arias-Rodriguez, I., Poon, K., Caro, A., and
M. Tuexen, "Stream Control Transmission Protocol (SCTP)
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
Parameter for the Stream Control Transmission Protocol
(SCTP)", RFC 4820, March 2007.

[I-D.ietf-tsvwg-sctp-auth]

[RFC4895] Tuexen, M., Stewart, R., Lei, P., and E. Rescorla,
"Authenticated Chunks for Stream Control Transmission
Protocol (SCTP)",
draft-ietf-tsvwg-sctp-auth-08 (work in progress),
February RFC 4895, August 2007.

[I-D.ietf-tsvwg-addip-sctp]

[RFC5061] Stewart, R., Xie, Q., Tuexen, M., Maruyama, S., and M.
Kozuka, "Stream Control Transmission Protocol (SCTP)
Dynamic Address Reconfiguration",
draft-ietf-tsvwg-addip-sctp-21 (work in progress), RFC 5061,
September 2007.

[RFC4960] Stewart, R., Ed., "Stream Control Transmission Protocol",
RFC 4960, June 2007.

13.2. Informative References

[effects]

[EFFECTS] Aura, T., Nikander, P., and G. Camarillo, "Effects of
Mobility and Multihoming on Transport-Layer Security",
Security and Privacy 2004, IEEE Symposium , URL http://
research.microsoft.com/users/tuomaura/Publications/
aura-nikander-camarillo-ssp04.pdf, May 2004.

Authors' Addresses

Randall R. Stewart
Cisco Systems, Inc.
4785 Forest Drive
Suite 200
Columbia, SC 29206
USA

Email:

EMail: rrs@cisco.com

Michael Tuexen
Muenster Univ. of Applied Sciences
Stegerwaldstr. 39
48565 Steinfurt
Germany

Email:

EMail: tuexen@fh-muenster.de

Gonzalo Camarillo
Ericsson
Hirsalantie 11
Jorvas 02420
Finland

Email:

EMail: Gonzalo.Camarillo@ericsson.com

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