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-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 =========================================================================== AUSCERT External Security Bulletin Redistribution ESB-2004.0637 -- iDEFENSE Security Advisory 10.11.04 Squid Web Proxy Cache Remote Denial of Service Vulnerability 12 October 2004 =========================================================================== AusCERT Security Bulletin Summary --------------------------------- Product: Squid Publisher: iDEFENSE Operating System: Linux variants UNIX variants Impact: Denial of Service Access: Remote/Unauthenticated CVE Names: CAN-2004-0918 Original Bulletin URL: http://www.idefense.com/application/poi/display?id=152 - --------------------------BEGIN INCLUDED TEXT-------------------- Squid Web Proxy Cache Remote Denial of Service Vulnerability iDEFENSE Security Advisory 10.11.04: www.idefense.com/application/poi/display?id=152&type=vulnerabilities October 11, 2004 I. BACKGROUND Squid Web Proxy Cache is a full-featured web proxy cache designed to run on Unix systems. It supports proxying HTTP, FTP, SSL, DNS, and has support for SNMP. II. DESCRIPTION Remote exploitation of a design error in the SNMP module of Squid Web Proxy Cache may lead to a denial of service. The problem specifically exists due to an ASN1 parsing error where certain header length combinations can slip through the validations performed by the ASN1 parser, eventually causing the server to restart and close all current connections. The server takes several seconds to restart. The offending code is in the asn_parse_header() routine of snmplib/asn1.c, which under some cases will allow negative length fields to pass validation. This leads to a failed xmalloc(), and the server then assumes there is heap corruption or some other exceptional condition, and restarts. III. ANALYSIS An attacker can exploit the above-described vulnerability to crash a Squid server. If the attack is repeated, it can render the server useless. Only a single UDP packet is required to trigger this vulnerability, so the source address can be spoofed. IV. DETECTION iDEFENSE has confirmed the existence of this vulnerability in Squid Web Proxy Cache version 2.5-STABLE5 compiled with SNMP support as well as Squid Web Proxy Cache version 3.0-PRE3-20040702 compiled with SNMP support. It is suspected that earlier versions are vulnerable as well. To find if a Squid binary is compiled with SNMP support one can run: grep snmp_port /usr/local/squid/sbin/squid If this command returns silently, that binary was not built with SNMP support and it is not vulnerable to this issue. V. WORKAROUND Disable SNMP support or filter the port that has SNMP processing activated (3401 by default) to allow only SNMP data from trusted hosts. To disable SNMP support on a squid binary that has SNMP support compiled in, use the entry snmp_port 0 in the squid.conf configuration file. To allow only the local interface to process SNMP, use the entry "snmp_incoming_address 127.0.0.1" in the squid.conf configuration file. Squid must be restarted to activate changes in the configuration file. VI. VENDOR RESPONSE Patch relative to Squid-2.5.STABLE6: http://www.squid-cache.org/Versions/v2/2.5/bugs/squid-2.5.STABLE6-SNMP_c ore_dump.patch Squid-2.5.STABLE7 release: ftp://ftp.squid-cache.org/pub/squid-2/STABLE/squid-2.5.STABLE7.tar.gz ftp://ftp.squid-cache.org/pub/squid-2/STABLE/squid-2.5.STABLE7.tar.bz2 http://www.squid-cache.org/Versions/v2/2.5/squid-2.5.STABLE7.tar.gz http://www.squid-cache.org/Versions/v2/2.5/squid-2.5.STABLE7.tar.bz2 or any of the mirrors http://www.squid-cache.org/Mirrors/ftp-mirrors.html http://www.squid-cache.org/Mirrors/http-mirrors.html VII. CVE INFORMATION The Common Vulnerabilities and Exposures (CVE) project has assigned the names CAN-2004-0918 to these issues. This is a candidate for inclusion in the CVE list (http://cve.mitre.org), which standardizes names for security problems. VIII. DISCLOSURE TIMELINE 09/15/2004 Initial vendor notification 09/15/2004 iDEFENSE clients notified 09/15/2004 Initial vendor response 10/05/2004 Coordinated public disclosure IX. CREDIT The discoverer of this vulnerability wishes to remain anonymous. Get paid for vulnerability research http://www.idefense.com/poi/teams/vcp.jsp X. LEGAL NOTICES Copyright (c) 2004 iDEFENSE, Inc. Permission is granted for the redistribution of this alert electronically. It may not be edited in any way without the express written consent of iDEFENSE. If you wish to reprint the whole or any part of this alert in any other medium other than electronically, please email customerservice@idefense.com for permission. Disclaimer: The information in the advisory is believed to be accurate at the time of publishing based on currently available information. Use of the information constitutes acceptance for use in an AS IS condition. There are no warranties with regard to this information. Neither the author nor the publisher accepts any liability for any direct, indirect, or consequential loss or damage arising from use of, or reliance on, this information. - --------------------------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. If you do not know who that is, please send an email to auscert@auscert.org.au and we will forward your request to the appropriate person. NOTE: Third Party Rights This security bulletin is provided as a service to AusCERT's members. As AusCERT did not write the document quoted above, AusCERT has had no control over its content. The decision to follow or act on information or advice contained in this security bulletin is the responsibility of each user or organisation, and should be considered in accordance with your organisation's site policies and procedures. AusCERT takes no responsibility for consequences which may arise from following or acting on information or advice contained in this security bulletin. NOTE: This is only the original release of the security bulletin. It may not be updated when updates to the original are made. If downloading at a later date, it is recommended that the bulletin is retrieved directly from the author's website to ensure that the information is still current. Contact information for the authors of the original document is included in the Security Bulletin above. If you have any questions or need further information, please contact them directly. 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: auscert@auscert.org.au 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 iQCVAwUBQWsSVih9+71yA2DNAQIINAP/T7EiJHdK3zPcJ70trdvG1fMcia+9QfcX 4fyavWIn7uFSX1bxjg1x+ubGjlCuqHClWpXbnJVOzG7NsKEICVLB8VAzr0aGTDb7 OKDNZKVLwhPJbzuhGYS97U6/hJRn+YehqBjhC2BWkmC0slJYfWhkq0tYmJiqUp1X 1l6pVhGaiaQ= =k7GT -----END PGP SIGNATURE-----