CVE-2004-0541 in Squid
Summary
by MITRE
Buffer overflow in the ntlm_check_auth (NTLM authentication) function for Squid Web Proxy Cache 2.5.x and 3.x, when compiled with NTLM handlers enabled, allows remote attackers to execute arbitrary code via a long password ("pass" variable).
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Analysis
by VulDB Data Team • 07/12/2025
The vulnerability described in CVE-2004-0541 represents a critical buffer overflow flaw within the Squid web proxy cache software that specifically affects versions 2.5.x and 3.x when configured with NTLM authentication handlers. This issue resides in the ntlm_check_auth function which processes authentication requests using the NTLM protocol, a widely deployed authentication mechanism in Windows environments. The flaw manifests when the system processes a maliciously crafted password string that exceeds the allocated buffer space, creating conditions that enable arbitrary code execution. The vulnerability is particularly dangerous because it allows remote attackers to exploit the proxy server without requiring local access or prior authentication, making it a significant threat to network security infrastructure.
The technical implementation of this buffer overflow occurs within the NTLM authentication processing logic where the pass variable containing the password is handled without proper bounds checking. When an attacker sends an authentication request with an excessively long password string, the system fails to validate the input length against the fixed buffer size allocated for the pass variable. This classic buffer overflow condition enables attackers to overwrite adjacent memory locations, potentially corrupting program execution flow and allowing the injection of malicious code. The vulnerability is classified under CWE-121 as a stack-based buffer overflow, where the insecure memory operation occurs in a stack allocated buffer during authentication processing. The flaw demonstrates poor input validation practices and inadequate bounds checking mechanisms that are fundamental requirements for secure software development.
The operational impact of this vulnerability extends beyond simple code execution to potentially compromise entire network infrastructures that rely on Squid proxy servers for authentication and access control. Attackers can leverage this vulnerability to gain unauthorized access to systems behind the proxy, escalate privileges, or establish persistent backdoors within the network. The remote exploitation capability means that attackers can target vulnerable Squid installations from anywhere on the internet, making this vulnerability particularly attractive for automated attacks. Organizations using Squid with NTLM authentication enabled face significant risk of data breaches, unauthorized access to internal resources, and potential lateral movement within their networks. This vulnerability directly impacts the CIA triad by compromising confidentiality through unauthorized access, integrity through potential code injection, and availability through possible service disruption.
Mitigation strategies for CVE-2004-0541 require immediate action including patching the software to the latest stable versions where the buffer overflow has been addressed. Organizations should disable NTLM authentication handlers in Squid when they are not required, as this eliminates the attack surface entirely. Network segmentation and access controls should be implemented to limit exposure of vulnerable proxy servers to untrusted networks. Security monitoring should be enhanced to detect unusual authentication patterns or potential exploitation attempts. The vulnerability aligns with ATT&CK technique T1078 which covers valid accounts and T1059 for command and scripting interpreter, as successful exploitation would allow attackers to execute commands and potentially establish persistent access. Regular security audits and input validation testing should be implemented to identify similar vulnerabilities in other software components, as this type of buffer overflow represents a common class of security flaws that require systematic detection and remediation approaches.