CVE-2011-4963 in nginx
Summary
by MITRE
nginx/Windows 1.3.x before 1.3.1 and 1.2.x before 1.2.1 allows remote attackers to bypass intended access restrictions and access restricted files via (1) a trailing . (dot) or (2) certain "$index_allocation" sequences in a request.
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Analysis
by VulDB Data Team • 12/07/2021
The vulnerability described in CVE-2011-4963 represents a critical path traversal flaw affecting nginx web server versions 1.3.x prior to 1.3.1 and 1.2.x prior to 1.2.1 on Windows platforms. This security issue stems from inadequate input validation in the web server's file handling mechanisms, specifically when processing HTTP requests containing malformed path sequences. The vulnerability enables remote attackers to circumvent access controls and retrieve files that should be restricted or protected within the web server's document root directory.
The technical exploitation occurs through two distinct methods that leverage the web server's interpretation of special characters in file path requests. The first method involves appending a trailing dot character to file paths, which the vulnerable nginx version fails to properly sanitize or normalize before attempting to access the requested resource. The second method exploits specific "$index_allocation" sequences within requests that can manipulate how the server resolves file paths, effectively allowing attackers to navigate beyond the intended document root boundaries. Both attack vectors exploit the fundamental weakness in path resolution logic that fails to properly validate or canonicalize file paths before file system operations are performed.
From an operational impact perspective, this vulnerability creates a severe security risk for organizations using affected nginx versions on Windows systems. Attackers can potentially access sensitive files including configuration files, database credentials, application source code, and other restricted content that should remain protected from unauthorized access. The vulnerability is particularly dangerous in environments where nginx serves dynamic content or where sensitive data is stored within the web server's accessible directories. The remote nature of the attack means that exploitation does not require local system access or authentication, making it an attractive target for automated attacks and security breaches.
This vulnerability aligns with CWE-22 Path Traversal and CWE-77 Path Traversal in the Common Weakness Enumeration catalog, specifically addressing the improper neutralization of special elements in path names. The attack pattern corresponds to T1083 File and Directory Discovery in the MITRE ATT&CK framework, as it enables adversaries to enumerate and access restricted file system resources. Organizations should prioritize immediate patching of affected nginx installations and implement additional security controls such as web application firewalls, proper input validation, and regular security assessments to prevent exploitation of this and similar path traversal vulnerabilities.
Mitigation strategies should include immediate deployment of nginx version 1.3.1 or 1.2.1 and later, which contain the necessary fixes to properly handle path normalization and validation. System administrators should also implement additional protective measures such as restricting file permissions on web server directories, implementing proper access control lists, and conducting regular security audits of web server configurations. The vulnerability underscores the importance of proper input sanitization and path validation in web server implementations, particularly in environments where multiple operating systems and file systems interact with web server components. Organizations should also consider implementing automated monitoring and alerting for suspicious file access patterns that may indicate exploitation attempts.