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.
Andrew, please bump to 2.5STABLE7.
STABLE7 just commited to cvs ...
Committed stable by maintainer... Ready for a GLSA
GLSA 200410-15
