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-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 =========================================================================== AUSCERT External Security Bulletin Redistribution ESB-2005.0312 -- IBM Security Advisory Various communication protocol vulnerabilities 18 April 2005 =========================================================================== 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 - --------------------------BEGIN INCLUDED TEXT-------------------- - -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 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 22.214.171.124 IY70027_04.040705.epkg.Z 5200-04 bos.net.tcp.client 126.96.36.199 bos.adt.include 188.8.131.52 IY70027_05.040705.epkg.Z 5200-05 bos.net.tcp.client 184.108.40.206 IY70026_01.040705.epkg.Z 5300-01 bos.net.tcp.client 220.127.116.11 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 firstname.lastname@example.org 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: email@example.com To request the PGP public key that can be used to communicate securely with the AIX Security Team send email to firstname.lastname@example.org 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. - -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.6 (GNU/Linux) iD8DBQFCW9FQxwSSvpORwfIRAjDqAJ4kCA0wROrXb4r6Ym2jcz5TkFMN3wCfeV8t AoI5hwPicXc3lAJI+5RLepA= =B2kk - -----END PGP SIGNATURE----- - --------------------------END INCLUDED TEXT-------------------- You have received this e-mail bulletin as a result of your organisation's registration with AusCERT. The mailing list you are subscribed to is maintained within your organisation, so if you do not wish to continue receiving these bulletins you should contact your local IT manager. 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Previous advisories and external security bulletins can be retrieved from: http://www.auscert.org.au/render.html?cid=1980 If you believe that your computer system has been compromised or attacked in any way, we encourage you to let us know by completing the secure National IT Incident Reporting Form at: http://www.auscert.org.au/render.html?it=3192 =========================================================================== Australian Computer Emergency Response Team The University of Queensland Brisbane Qld 4072 Internet Email: firstname.lastname@example.org Facsimile: (07) 3365 7031 Telephone: (07) 3365 4417 (International: +61 7 3365 4417) AusCERT personnel answer during Queensland business hours which are GMT+10:00 (AEST). On call after hours for member emergencies only. =========================================================================== -----BEGIN PGP SIGNATURE----- Comment: http://www.auscert.org.au/render.html?it=1967 iQCVAwUBQmM01Ch9+71yA2DNAQKVZgQAhh4TYgNYLfq5eHjWhroorbsHCoGOR1nZ siFOpVlzKvSCSwo2moKI9t6RLRMW/kJ6M0/BJR9FZ3gltJ5fXlvU4lF7sCpekmNd L9qw4LhiqtGGaJOPlVp4C+GVguvtjWILJCBBwdY2Leygr9JNZX1PILAXNHn5e+bG +1RyGvINrdQ= =o9Qk -----END PGP SIGNATURE-----