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AUSCERT External Security Bulletin Redistribution
ESB-2005.0312 -- IBM Security Advisory
Various communication protocol vulnerabilities
18 April 2005
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AusCERT Security Bulletin Summary
---------------------------------
Publisher: IBM
Operating System: AIX 5.1 5.2 and 5.3
Impact: Denial of Service
Reduced Security
Access: Remote/Unauthenticated
CVE Names: CAN-2004-1060 CAN-2004-0791 CAN-2004-0790
CAN-2004-0230
Ref: ESB-2005.0305
ESB-2005.0294
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IBM SECURITY ADVISORY
First Issued: Tue Apr 12 13:46:38 UTC 2005
==========================================================================
VULNERABILITY SUMMARY
VULNERABILITY: Various communication protocol vulnerabilities.
PLATFORMS: AIX 5.1, 5.2 and 5.3
SOLUTION: Apply the workarounds, efixs or APARs as described
below.
THREAT: Remote attackers may be able to cause performance
degradation or a denial of service.
CERT VU Number: VU#222750, VU#415294
NISCC: Advisory #532967, #236929
CVE: CAN-2004-1060, CAN-2004-0791, CAN-2004-0230
US-CERT: TA04-111A
==========================================================================
DETAILED INFORMATION
I. Description
===============
This advisory addresses various vulnerabilities in the TCP, ICMP and IP
protocols.
ICMP Vulnerabilities
- - - --------------------
Vulnerabilities have been discovered in ICMP that can be exploited to reset
arbitrary TCP connections (blind connection-reset attacks, CAN-2004-0790)
or reduce the throughput between two hosts that rely on IP to communicate
(blind throughput-reduction attacks). The ICMP vulnerabilities correspond
to the vulnerabilities discussed in NISCC Advisory #532967 and CERT
Vulnerability Note VU#222750. AIX 5L is not vulnerable to the blind
connection-reset vulnerability. There are two known blind
throughput-reduction attacks: the ICMP Source Quench attack (CAN-2004-0791)
and the ICMP attack against the PMTU Discovery mechanism (CAN-2004-1060).
AIX is affected by both blind throughput-reduction attacks. A detailed
discussion of these ICMP vulnerabilities can be found in an IETF draft
which is currently available at
http://www.ietf.org/internet-drafts/draft-gont-tcpm-icmp-attacks-03.txt.
TCP Vulnerabilities
- - - -------------------
Vulnerabilities have been reported in TCP (US-CERT TA04-111A, CERT
VU#415294, NISCC Advisory #236929, CAN-2004-0230).
The vulnerabilities discussed include issues that allow an attacker to
cause arbitrary TCP connections to end prematurely (blind reset attack) or
inject arbitrary data into a TCP stream (blind data injection attack).
There are two variations of the blind reset attack. One variation, the
blind reset attack using the RST bit, allows an attacker to reset a
connection if the RST bit is set and the sequence number can be predicted.
The second variation, the blind reset attack using the SYN bit, allows an
attacker to tear down a connection if he sends a SYN packet to a host and
successfully associates this packet with a connection in the ESTABLISHED
state as described below. Note that several pre-conditions must exist for
an attacker to successfully exploit these vulnerabilities. First, the
attacker must guess source and destination IP addresses and port numbers.
Second, the attacker must craft a TCP packet with a sequence number within
a given range. Third, the TCP connection must exist long enough for an
attacker to predict a TCP sequence number. Many applications use TCP in a
manner that makes it very difficult for an attacker to fulfill these
pre-conditions. A detailed discussion of these TCP vulnerabilities can be
found in an IETF draft which is currently available at
http://www.ietf.org/internet-drafts/draft-ietf-tcpm-tcpsecure-02.txt.
IP Vulnerabilities
- - - ------------------
IP Fragmentation attacks are attacks that send a large number of IP
fragments to a host in an attempt to cause performance degradation or a
denial of service.
II. Impact
==========
ICMP Vulnerabilities
- - - --------------------
The blind throughput-reduction attacks can both be exploited to reduce the
throughput of a TCP connection.
TCP Vulnerabilities
- - - -------------------
An attacker may cause an existing TCP connection to terminate prematurely
or inject arbitrary data into an existing TCP stream.
IP Vulnerabilities
- - - ------------------
An attacker may cause performance degradation resulting in a denial of
service.
III. Solutions
===============
A. Official Fix
IBM provides the following fixes:
ICMP Vulnerabilities
- - - --------------------
APAR number for AIX 5.1.0: IY70028 (available approx. 08/03/05)
APAR number for AIX 5.2.0: IY70027 (available approx. 06/01/05)
APAR number for AIX 5.3.0: IY70026 (available approx. 05/18/05)
These fixes introduce a new network option that can be set using the "no"
(network options) command. The option name is "tcp_icmpsecure" and it can
be enabled using the following command:
# no -o tcp_icmpsecure=1
This option is off by default.
TCP Vulnerabilities
- - - -------------------
APAR number for AIX 5.1.0: IY55950 (available)
APAR number for AIX 5.2.0: IY55949 (available)
APAR number for AIX 5.3.0: IY62006 (available)
These fixes introduce a new network option that can be set using the "no"
command. The option name is "tcp_tcpsecure" and it can be enabled using
the following command:
# no -o tcp_icmpsecure=X
Note that X must be a value between 0 and 7; this option is off by default.
The following table documents the effect for different values of X.
tcp_tcpsecure Value Issue addressed
==========================================================================
0 None
1 Blind reset attack using the RST bit
2 Blind reset attack using the SYN bit
3 Both issues addressed by tcp_tcpsecure value 1 and 2
4 Blind data injection attack
5 Both issues addressed by tcp_tcpsecure value 1 and 4
6 Both issues addressed by tcp_tcpsecure value 2 and 4
7 Issues addressed by tcp_tcpsecure values 1, 2 and 4
IP Vulnerabilities
- - - ------------------
APAR number for AIX 5.1.0: IY63365 (available)
APAR number for AIX 5.2.0: IY63364 (available)
APAR number for AIX 5.3.0: IY63363 (available)
These fixes introduce a new network option that can be set using the "no"
command. The option name is "ip_nfrag" and it can be enabled using the
following command:
# no -o ip_nfrag=X
ip_nfrag specifies the maximum number of fragments of an IP packet that can
be kept in the IP reassembly queue at any time. The default value of this
network option is 200 with which is a reasonable value for most
environments and which offers protection from IP fragmentation attacks.
NOTE: Affected customers are urged to upgrade to 5.1.0, 5.2.0 or 5.3.0 at
the latest maintenance level.
B. Emergency Fix
Efixes are available. The efixes can be downloaded via ftp from:
ftp://aix.software.ibm.com/aix/efixes/security/icmp_efix.tar.Z
icmp_efix.tar.Z is a compressed tarball containing this advisory, four
efix packages and a cleartext PGP signature for each efix package. The
following table maps the efix package to the AIX Maintenance Packages and
fileset prerequisites necessary to install the efixes. The prerequisite
filesets must be installed on top of the listed AIX Maintenance Packages.
IY70027_04.040705.epkg.Z addresses the ICMP, TCP and IP vulnerabilities.
The other efixes only address the ICMP vulnerabilities since the
prerequisites for these efixes include fixes for the TCP vulnerabilities
and IP vulnerabilities.
Filename AIX Maintenance Prerequisite
Package
==========================================================================
IY70028_07.040705.epkg.Z 5100-07 bos.net.tcp.client 5.1.0.66
IY70027_04.040705.epkg.Z 5200-04 bos.net.tcp.client 5.2.0.43
bos.adt.include 5.2.0.43
IY70027_05.040705.epkg.Z 5200-05 bos.net.tcp.client 5.2.0.52
IY70026_01.040705.epkg.Z 5300-01 bos.net.tcp.client 5.3.0.10
Verify you have retrieved the efixes intact:
- - - --------------------------------------------
The checksums below were generated using the "sum" and "md5sum" commands
and are as follows:
Filename sum md5
========================================================================
IY70026_01.040705.epkg.Z 57890 572 c9d0d9b1c78fa30ec950d4199fbdfb91
IY70027_04.040705.epkg.Z 21321 538 21e413ec1dd25c5cb38b284988453747
IY70027_05.040705.epkg.Z 12738 541 dcea6831c314d4eb2791eff9cb9bd53a
IY70028_07.040705.epkg.Z 59897 518 84ec1447d0ad56cc9b053b757d160bc2
These sums should match exactly. The PGP signatures in the compressed
tarball and on this advisory can also be used to verify the integrity of
the various files they correspond to. If the sums or signatures cannot be
confirmed, double check the command results and the download site address.
If those are OK, contact IBM AIX Security at security-alert@austin.ibm.com
and describe the discrepancy.
IMPORTANT: If possible, it is recommended that a mksysb backup of the
system is created. Verify it is both bootable, and readable before
proceeding.
These efixes have not been fully regression tested; thus, IBM does not
warrant the fully correct functioning of the efix. Customers install the
efix and operate the modified version of AIX at their own risk.
Efix Installation Instructions:
- - - -------------------------------
Please note that these efix packages will require the prerequisites listed
above to install successfully and that a reboot is required for these
changes to take effect. After installing the efix, it is necessary to
tune the appropriate network options as described above.
These packages use the new Emergency Fix Management Solution to install
and manage efixes. More information can be found at:
http://techsupport.services.ibm.com/server/aix.efixmgmt
To preview an epkg efix installation execute the following command:
# emgr -e epkg_name -p # where epkg_name is the name of the
# efix package being previewed.
To install an epkg efix package, execute the following command:
# emgr -e epkg_name -X # where epkg_name is the name of the
# efix package being installed.
The "X" flag will expand any filesystems if required.
C. Workaround
ICMP Vulnerabilities
- - - --------------------
ICMP Source Quench blind throughput-reduction attack can be mitigated by
using firewall rules to block ICMP Souce Quench packets.
TCP Vulnerabilities
- - - -------------------
Ingress filtering can be caused to prevent IP source address spoofing.
Another approach is to use small tcp windows. This can be done by turning
the network option "rfc1323" off using the "no" command. This will not
ensure total protection against these vulnerabilities but it will reduce
the probablity that they can be exploited.
IV. Obtaining Fixes
===================
AIX Version 5 APARs can be downloaded from:
http://www-1.ibm.com/servers/eserver/support/pseries/aixfixes.html
Security related Emergency Fixes can be downloaded from:
ftp://aix.software.ibm.com/aix/efixes/security
V. Contact Information
========================
If you would like to receive AIX Security Advisories via email, please
visit:
https://techsupport.services.ibm.com/server/pseries.subscriptionSvcs
Comments regarding the content of this announcement can be directed to:
security-alert@austin.ibm.com
To request the PGP public key that can be used to communicate securely
with the AIX Security Team send email to security-alert@austin.ibm.com
with a subject of "get key". The key can also be downloaded from a PGP
Public Key Server. The key id is 0x9391C1F2.
Please contact your local IBM AIX support center for any assistance.
eServer is a trademark of International Business Machines Corporation.
IBM, AIX and pSeries are registered trademarks of International Business
Machines Corporation. All other trademarks are property of their
respective holders.
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