CVE-2005-0446 in Squid
Summary
by MITRE
Squid 2.5.STABLE8 and earlier allows remote attackers to cause a denial of service (crash) via certain DNS responses regarding (1) Fully Qualified Domain Names (FQDN) in fqdncache.c or (2) IP addresses in ipcache.c, which trigger an assertion failure.
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Analysis
by VulDB Data Team • 07/05/2025
The vulnerability identified as CVE-2005-0446 represents a critical denial of service flaw affecting Squid proxy server versions 2.5.STABLE8 and earlier. This issue stems from inadequate input validation within the DNS resolution mechanisms of the proxy software, specifically targeting the fqdn cache and ip cache components. The vulnerability operates through malformed DNS responses that exploit weak assertion checks in the software's caching subsystem, leading to unexpected program termination and system unavailability.
The technical implementation of this vulnerability occurs in two distinct code paths within the Squid source code. The first pathway involves manipulation of Fully Qualified Domain Names within the fqdncache.c module, where the software fails to properly validate DNS response formats when caching domain name lookups. The second pathway targets IP address caching in ipcache.c, where similar assertion failures occur when processing malformed IP address responses. Both scenarios trigger assertion failures that cause the Squid process to crash, effectively rendering the proxy service unavailable to legitimate users.
From an operational perspective, this vulnerability presents significant risk to organizations relying on Squid as a critical network infrastructure component. Attackers can remotely exploit this flaw by crafting malicious DNS responses that, when processed by the vulnerable Squid server, result in immediate service disruption. The impact extends beyond simple availability issues as the crash can occur without any authentication requirements, making it particularly dangerous in environments where DNS spoofing or man-in-the-middle attacks are possible. Network administrators face the challenge of maintaining service availability while dealing with an attack vector that requires no privileged access or complex exploitation techniques.
The vulnerability aligns with CWE-617, which addresses reachable assertions, and demonstrates characteristics consistent with CWE-122, concerning buffer overflow conditions, even though the specific manifestation is an assertion failure rather than memory corruption. From an ATT&CK framework perspective, this vulnerability maps to T1499.004, which covers network disruption attacks, and potentially T1595.001, related to network sniffing techniques that could be employed to craft the malicious DNS responses. The attack surface is particularly concerning given that Squid is widely deployed in enterprise environments as a caching proxy, web filter, and content accelerator, making successful exploitation capable of disrupting substantial network traffic.
Mitigation strategies for this vulnerability require immediate patching of affected Squid installations to versions 2.5.STABLE9 or later, which contain the necessary fixes for the assertion failure conditions. Network administrators should also implement DNS security measures including DNSSEC validation and monitoring for unusual DNS traffic patterns that might indicate exploitation attempts. Additional protective measures include implementing network segmentation to limit exposure, deploying intrusion detection systems capable of identifying DNS response anomalies, and establishing robust monitoring procedures to detect service disruption events. Organizations should also consider implementing redundant proxy infrastructure to maintain service availability during patching operations and to provide failover capabilities when dealing with such critical vulnerabilities.