CVE-2012-5100 in HServer
Summary
by MITRE
Directory traversal vulnerability in HServer 0.1.1 allows remote attackers to read arbitrary files via a (1) ..%5c (dot dot encoded backslash) or (2) %2e%2e%5c (encoded dot dot backslash) in the PATH_INFO.
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Analysis
by VulDB Data Team • 08/26/2025
The vulnerability identified as CVE-2012-5100 represents a critical directory traversal flaw within HServer version 0.1.1, a lightweight web server implementation that has been widely deployed in various network environments. This weakness stems from inadequate input validation mechanisms that fail to properly sanitize user-supplied path information, specifically within the PATH_INFO parameter. The vulnerability manifests when the server processes requests containing specially crafted directory traversal sequences that bypass normal path resolution mechanisms, allowing unauthorized access to files outside the intended web root directory.
The technical exploitation of this vulnerability relies on specific encoding techniques that manipulate how the web server interprets path components. Attackers can utilize two primary methods to exploit this flaw: the first involves using ..%5c sequences where the %5c represents the encoded backslash character, while the second employs %2e%2e%5c combinations where the %2e sequences represent encoded dots. Both approaches leverage the server's insufficient validation of encoded path sequences, allowing the traversal logic to interpret these encoded sequences as legitimate directory navigation commands rather than malicious input. This encoding bypass technique demonstrates a fundamental flaw in the server's request parsing and path validation implementation.
From an operational perspective, this vulnerability poses significant security risks to systems running affected HServer versions, as it enables remote attackers to access sensitive files including configuration data, user credentials, application source code, and other potentially confidential information. The impact extends beyond simple file access, as successful exploitation can lead to complete system compromise through the retrieval of administrative credentials, database connection strings, or application logic that could facilitate further attacks. The remote nature of this vulnerability means that attackers do not require physical access to the system, making it particularly dangerous in environments where the server is exposed to untrusted networks.
The vulnerability aligns with CWE-22, which describes improper limitation of a pathname to a restricted directory, commonly known as path traversal or directory traversal. This classification indicates that the flaw resides in the fundamental design of path validation mechanisms within the web server implementation. Additionally, the attack pattern corresponds to techniques documented in the ATT&CK framework under T1083, which covers File and Directory Discovery, and T1566, which encompasses Phishing with Malicious Attachments, as attackers may use this vulnerability to obtain sensitive information for further exploitation. Organizations utilizing affected HServer versions should immediately implement mitigations including input validation, path normalization, and proper access controls to prevent unauthorized file access and maintain system integrity.
The remediation approach for this vulnerability requires immediate patching of the HServer software to version 0.1.2 or later, which includes proper input sanitization and path validation mechanisms. System administrators should also implement network-level controls including firewall rules that restrict access to the web server, input filtering at the application level, and regular security audits to identify similar vulnerabilities in other components of the web infrastructure. Organizations should conduct comprehensive vulnerability assessments to identify any other applications or services that might be susceptible to similar directory traversal attacks, as this type of flaw often indicates broader architectural issues in input validation and access control implementations.