CVE-2005-0194 in proxy
Summary
by MITRE
Squid 2.5, when processing the configuration file, parses empty Access Control Lists (ACLs), including proxy_auth ACLs without defined auth schemes, in a way that effectively removes arguments, which could allow remote attackers to bypass intended ACLs if the administrator ignores the parser warnings.
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Analysis
by VulDB Data Team • 10/29/2024
The vulnerability described in CVE-2005-0194 affects Squid proxy server version 2.5 and represents a critical configuration parsing flaw that undermines the security controls implemented through Access Control Lists. This issue manifests when Squid processes configuration files containing empty ACLs, particularly proxy_auth ACLs that lack defined authentication schemes. The flaw occurs during the parser's handling of these malformed configurations, where arguments are effectively stripped from the ACL definitions, creating a dangerous security gap in the proxy's access control mechanisms.
The technical implementation of this vulnerability stems from Squid's configuration parser failing to properly validate ACL definitions before processing them. When the parser encounters empty ACLs or proxy_auth ACLs without specified authentication schemes, it removes or ignores the arguments associated with these definitions. This behavior creates a scenario where ACL rules that should restrict access are effectively neutralized, allowing unauthorized access to proxy resources. The parser warnings generated during this process are often ignored by administrators, making the vulnerability particularly insidious as it can remain undetected in production environments.
The operational impact of this vulnerability is significant for organizations relying on Squid as their primary proxy server. Attackers can exploit this flaw to bypass authentication requirements and access restricted resources through the proxy server, potentially gaining access to internal networks, sensitive data, or bypassing content filtering controls. The vulnerability essentially allows remote attackers to perform privilege escalation by manipulating the proxy's access control mechanisms, which could lead to unauthorized data access, network infiltration, or complete compromise of the proxy server's security posture.
This vulnerability aligns with CWE-254 in the Common Weakness Enumeration, which categorizes it as a "Security Feature Missing" weakness, specifically involving inadequate input validation and processing of security-relevant configuration parameters. The flaw also maps to ATT&CK technique T1078.002, "Valid Accounts: Password Policy Enforcement," as it effectively bypasses authentication controls that should be enforced through proxy authentication mechanisms. Organizations should implement immediate mitigation strategies including updating to patched versions of Squid, implementing strict configuration validation procedures, and monitoring for parser warnings that indicate potential security gaps in ACL definitions. The vulnerability underscores the importance of proper input validation and configuration file parsing in security-critical applications, demonstrating how seemingly minor parser flaws can create substantial security risks in network infrastructure components.