CVE-2008-0633 in Anon Proxy Server
Summary
by MITRE
Buffer overflow in Anon Proxy Server 0.102 and earlier, when user authentication is enabled, allows remote attackers to cause a denial of service (exception) via a user name with a large number of quotes, which triggers the overflow during escaping.
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Analysis
by VulDB Data Team • 01/05/2025
The vulnerability identified as CVE-2008-0633 represents a critical buffer overflow flaw within the Anon Proxy Server software version 0.102 and earlier implementations. This security weakness specifically manifests when the proxy server operates with user authentication enabled, creating a pathway for remote attackers to exploit the system through carefully crafted input manipulation. The flaw occurs during the username processing phase, where the system fails to properly validate or limit the length of input characters, particularly focusing on quote characters that require escaping operations. The buffer overflow vulnerability arises from insufficient bounds checking during the escaping procedure, which is a fundamental security mechanism designed to handle special characters in user input. This particular implementation flaw demonstrates poor input sanitization practices that directly violate established security principles for handling user-provided data in network services.
The technical exploitation of this vulnerability requires attackers to submit a username containing an excessive number of quote characters that, when processed through the server's escaping mechanism, exceed the allocated buffer space. During the escaping process, each quote character typically requires additional processing and often expansion in the output buffer, leading to a scenario where the cumulative effect of multiple quotes causes the buffer to overflow. This overflow results in an exception being thrown within the application's execution context, ultimately leading to a denial of service condition that disrupts the proxy server's normal operations. The vulnerability operates at the application layer and specifically targets the authentication handling component, making it particularly dangerous as it can affect legitimate users attempting to access the proxy service. The issue is classified as a classic buffer overflow vulnerability that can be categorized under CWE-121, which describes stack-based buffer overflow conditions, and potentially CWE-122 for heap-based buffer overflow scenarios depending on the specific implementation details.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise the overall availability and integrity of the proxy infrastructure. When exploited successfully, the buffer overflow causes the Anon Proxy Server to crash or terminate unexpectedly, forcing administrators to restart the service manually and potentially disrupting legitimate user sessions. This denial of service condition affects the availability of the proxy service for all users, including those who may be using the system for legitimate purposes such as anonymous browsing or bypassing network restrictions. The vulnerability's remote exploitability means that attackers can initiate the attack from anywhere on the network without requiring local system access or credentials, making it particularly dangerous in environments where the proxy server is exposed to untrusted networks. The flaw also demonstrates weaknesses in the server's input validation mechanisms, which may indicate broader security issues in the codebase that could be exploited for more severe attacks. Organizations relying on this proxy server for network access control and privacy protection face significant risks, as the vulnerability could be leveraged to disrupt services or potentially serve as a stepping stone for more sophisticated attacks against the underlying network infrastructure.
Mitigation strategies for this vulnerability should focus on immediate patching of the Anon Proxy Server software to version 0.103 or later, which contains the necessary fixes for the buffer overflow condition. System administrators should implement input validation controls that limit the maximum length of usernames and restrict the number of special characters allowed in authentication credentials. The implementation of proper bounds checking during escaping operations and enhanced buffer management practices should be prioritized to prevent similar issues in other components of the system. Network segmentation and access controls should be implemented to limit exposure of the proxy server to untrusted networks, while monitoring systems should be deployed to detect potential exploitation attempts. Additionally, organizations should consider implementing application-level firewalls or intrusion detection systems that can identify and block suspicious username patterns that may indicate attempted exploitation. The vulnerability serves as a reminder of the importance of proper input validation and buffer management in network services, aligning with ATT&CK technique T1499 for network denial of service and emphasizing the need for secure coding practices. Regular security assessments and code reviews should be conducted to identify similar vulnerabilities in other network services and applications, ensuring comprehensive protection against buffer overflow exploits.