CVE-2008-4360 in lighttpd
Summary
by MITRE
mod_userdir in lighttpd before 1.4.20, when a case-insensitive operating system or filesystem is used, performs case-sensitive comparisons on filename components in configuration options, which might allow remote attackers to bypass intended access restrictions, as demonstrated by a request for a .PHP file when there is a configuration rule for .php files.
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Analysis
by VulDB Data Team • 08/02/2021
The vulnerability identified as CVE-2008-4360 affects the lighttpd web server software version 1.4.20 and earlier, specifically within the mod_userdir module. This issue arises from a fundamental mismatch in how the software handles filename component comparisons when operating on case-insensitive file systems or operating systems. The mod_userdir module is designed to provide user directory access control, typically allowing users to access their own directories through specific URL patterns. The flaw manifests when the web server processes configuration rules for file extensions, creating a security gap that can be exploited by malicious actors.
The technical implementation of this vulnerability stems from the inconsistent handling of case sensitivity in filename comparisons. When lighttpd processes requests for user directories, it performs case-sensitive comparisons on filename components within its configuration options. However, on case-insensitive operating systems or file systems, this approach creates a discrepancy where the server's internal logic does not align with the actual filesystem behavior. This mismatch allows attackers to craft requests using different case variations of file extensions that would normally be restricted by configuration rules.
The operational impact of this vulnerability is significant as it enables unauthorized access to user directories and potentially sensitive files. An attacker can exploit this by making requests using uppercase file extensions when the configuration only specifies lowercase extensions, effectively bypassing access controls that were intended to restrict file access. This vulnerability specifically demonstrates the risk of improper input validation and the importance of consistent case handling in security-sensitive applications. The issue directly relates to CWE-691, which addresses insufficient control of code generation or execution, and CWE-707, covering improper control of generation of code, as the flawed comparison logic leads to unintended code execution paths.
The attack vector for this vulnerability involves sending specially crafted HTTP requests to the web server, where the attacker manipulates the case of file extensions in their requests. When the server processes these requests, the case-sensitive comparison logic fails to properly match against the configuration rules, allowing access to files that should otherwise be restricted. This type of vulnerability is particularly dangerous in multi-user environments where user directories contain sensitive information. The exploitation aligns with ATT&CK technique T1078.004, which covers valid accounts using unprivileged accounts, as the bypass occurs through legitimate access mechanisms rather than brute force or privilege escalation.
Mitigation strategies for this vulnerability include upgrading to lighttpd version 1.4.20 or later, which contains the fix for this specific issue. System administrators should also implement proper configuration management practices, ensuring that all file extension rules are consistently defined regardless of case variations. Additional protective measures include deploying web application firewalls that can detect and block suspicious case variations in file requests, implementing proper access controls at the filesystem level, and conducting regular security audits to identify similar inconsistencies in other applications. Organizations should also consider implementing automated tools that can detect such case-sensitivity issues in their web server configurations to prevent similar vulnerabilities from being introduced in future deployments.