CVE-2005-2917 in Squid
Summary
by MITRE
Squid 2.5.STABLE10 and earlier, while performing NTLM authentication, does not properly handle certain request sequences, which allows attackers to cause a denial of service (daemon restart).
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Analysis
by VulDB Data Team • 06/29/2025
The vulnerability identified as CVE-2005-2917 affects Squid proxy servers version 2.5.STABLE10 and earlier, specifically within the NTLM authentication mechanism. This flaw represents a significant security concern as it enables malicious actors to disrupt service availability through carefully crafted request sequences that exploit improper handling of authentication protocols. The vulnerability resides in the daemon's processing of NTLM authentication challenges and responses, creating a condition where specific request patterns can trigger unexpected behavior in the proxy server's authentication subsystem.
The technical implementation of this vulnerability stems from insufficient input validation and error handling within Squid's NTLM authentication module. When processing certain sequences of NTLM authentication requests, the daemon fails to properly validate the structure and content of authentication messages, leading to a condition where malformed or unexpected request patterns cause the authentication process to fail catastrophically. This failure manifests as an automatic daemon restart, effectively creating a denial of service condition that can be repeatedly triggered by an attacker. The flaw operates at the protocol level where the authentication sequence does not adequately sanitize incoming NTLM messages, allowing attackers to craft specific request combinations that exploit memory handling inconsistencies.
The operational impact of this vulnerability extends beyond simple service disruption as it can be exploited remotely without requiring authentication credentials, making it particularly dangerous in environments where Squid serves as a critical proxy infrastructure component. Network administrators may experience frequent service interruptions, potentially affecting thousands of concurrent users depending on the proxy server's deployment. The automatic daemon restart behavior creates a cascading effect where legitimate users experience intermittent connectivity issues while the service continuously restarts, potentially leading to increased system load and resource exhaustion. This vulnerability is particularly concerning in enterprise environments where proxy servers handle critical business traffic and where service availability is paramount.
Organizations should implement immediate mitigations including upgrading to Squid versions 2.5.STABLE11 or later, which contain patches addressing the NTLM authentication handling flaw. Network administrators should also consider implementing rate limiting mechanisms and authentication request monitoring to detect and prevent exploitation attempts. The vulnerability aligns with CWE-20, representing a weakness in input validation, and can be categorized under ATT&CK technique T1499.004 for network denial of service attacks. Additionally, implementing proper access controls and limiting NTLM authentication to trusted networks can reduce exposure. Security teams should also monitor for exploitation attempts by analyzing proxy logs for unusual authentication request patterns and implement intrusion detection systems to identify potential exploitation attempts. Regular security assessments of proxy server configurations and authentication mechanisms should be conducted to identify similar vulnerabilities in other components of the network infrastructure.