CVE-2005-0453 in lighttpd
Summary
by MITRE
The buffer_urldecode function in Lighttpd 1.3.7 and earlier does not properly handle control characters, which allows remote attackers to obtain the source code for CGI and FastCGI scripts via a URL with a %00 (null) character after the file extension.
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Analysis
by VulDB Data Team • 06/05/2019
The vulnerability identified as CVE-2005-0453 represents a critical buffer handling flaw in the Lighttpd web server software version 1.3.7 and earlier. This issue stems from improper validation of control characters within the buffer_urldecode function, which is responsible for processing URL-encoded data. The flaw specifically manifests when a null character %00 is inserted after a file extension in a URL request, creating a condition that can be exploited by remote attackers to gain unauthorized access to sensitive server resources.
The technical implementation of this vulnerability exploits the inadequate input sanitization mechanisms within Lighttpd's URL decoding process. When the buffer_urldecode function encounters a null character within a URL, it fails to properly terminate string processing or validate the control character's presence. This improper handling allows the web server to interpret the URL in a manner that bypasses normal file access controls and potentially reveals the source code of CGI and FastCGI scripts that would otherwise be protected from direct access. The vulnerability is particularly dangerous because it leverages the fundamental URL encoding mechanism that web servers expect to handle safely, making it difficult to detect through standard security monitoring.
From an operational impact perspective, this vulnerability creates a significant security risk for organizations running affected Lighttpd versions, as it directly enables source code disclosure attacks that can expose sensitive application logic, configuration details, and potentially user data. The exploitation technique is straightforward and requires minimal skill, making it attractive to attackers who may seek to discover vulnerabilities in web applications or extract proprietary code. The vulnerability affects not only the web server's ability to maintain proper access controls but also potentially compromises the confidentiality of applications hosted on the server, particularly those utilizing CGI and FastCGI interfaces where source code exposure could reveal implementation details that aid in further exploitation attempts.
The vulnerability aligns with CWE-121, which addresses buffer overflow conditions in the context of control characters and improper input validation, and demonstrates characteristics consistent with attack patterns documented in the MITRE ATT&CK framework under the T1190 technique for exploitation of remote services. Organizations affected by this vulnerability should prioritize immediate patching to version 1.3.8 or later, which includes proper input validation for control characters in URL decoding. Additional mitigations may include implementing web application firewalls to filter out null character sequences in URL requests, configuring proper access controls for CGI and FastCGI scripts, and monitoring for unusual URL patterns that might indicate exploitation attempts. Network segmentation and regular security assessments should also be employed to reduce the potential impact of such vulnerabilities in the broader security posture.