CVE-2004-2480 in Squid Web Proxy Cache
Summary
by MITRE
Squid Web Proxy Cache 2.3.STABLE5 allows remote attackers to bypass security controls and access arbitrary websites via "@@" sequences in a URL within Internet Explorer.
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Analysis
by VulDB Data Team • 12/28/2024
The vulnerability identified as CVE-2004-2480 affects Squid Web Proxy Cache version 2.3.STABLE5 and represents a significant security flaw that enables remote attackers to circumvent proxy security measures. This issue specifically targets the handling of URL parsing within the proxy server, creating a pathway for unauthorized access to restricted web content. The vulnerability exploits a weakness in how Squid processes certain URL sequences, allowing malicious actors to manipulate the proxy's behavior and gain access to websites that should otherwise be blocked or restricted.
The technical implementation of this vulnerability stems from improper URL parsing logic within the Squid proxy software. When Internet Explorer processes URLs containing "@" sequences, the proxy server fails to correctly interpret these special characters, leading to a bypass of the intended access controls. This flaw operates at the application layer and leverages the way the proxy handles malformed or specially crafted URL requests. The "@" sequence acts as a delimiter or escape mechanism that the proxy does not properly sanitize, allowing attackers to manipulate the URL structure and effectively bypass the proxy's filtering mechanisms. This issue falls under the category of input validation failures and can be classified as a CWE-20: Improper Input Validation, as the proxy does not adequately validate or sanitize incoming URL parameters.
The operational impact of this vulnerability extends beyond simple access bypass, as it fundamentally compromises the security posture of any network relying on Squid for web filtering and content control. Organizations using this version of Squid may experience unauthorized access to restricted websites, potentially exposing sensitive corporate data or allowing access to malicious content. The vulnerability is particularly dangerous in enterprise environments where web proxies are used to enforce security policies and restrict access to certain categories of websites. Attackers could exploit this weakness to access blocked resources, download malware, or conduct man-in-the-middle attacks against users who believe they are protected by the proxy's security controls. This flaw undermines the core purpose of web proxy services, which is to provide controlled access to internet resources while maintaining security boundaries.
Mitigation strategies for CVE-2004-2480 require immediate attention from system administrators and security teams. The most effective solution involves upgrading to a patched version of Squid that properly handles URL parsing and sanitizes special character sequences. Organizations should also implement additional network-level controls such as firewall rules that restrict access to known vulnerable proxy configurations and deploy intrusion detection systems that can identify suspicious URL patterns. Network administrators should consider implementing additional logging and monitoring of proxy activities to detect potential exploitation attempts. The vulnerability demonstrates the importance of proper input validation and sanitization in web applications, aligning with ATT&CK technique T1071.004 for Application Layer Protocol: DNS and T1566.001 for Phishing: Spearphishing Attachment. Organizations should also review their proxy configurations and implement more robust URL filtering mechanisms to prevent similar issues from occurring in other components of their security infrastructure. Regular security assessments and vulnerability scanning should be conducted to identify and remediate similar weaknesses in other network components that may be susceptible to similar input manipulation attacks.