CVE-2008-4359 in lighttpd
Summary
by MITRE
lighttpd before 1.4.20 compares URIs to patterns in the (1) url.redirect and (2) url.rewrite configuration settings before performing URL decoding, which might allow remote attackers to bypass intended access restrictions, and obtain sensitive information or possibly modify data.
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Analysis
by VulDB Data Team • 08/02/2021
The vulnerability identified as CVE-2008-4359 affects lighttpd web servers version 1.4.20 and earlier, presenting a significant security flaw in the handling of URI patterns within URL redirection and rewriting configurations. This issue stems from the server's improper sequence of operations during URI processing, where patterns are matched against raw, undecoded URIs rather than their properly decoded counterparts. The vulnerability falls under the category of improper input validation and pattern matching, which can be categorized as CWE-20, indicating a weakness in the web application's input handling mechanisms. Attackers can exploit this flaw by crafting malicious URIs that, when processed through the url.redirect and url.rewrite directives, bypass intended access controls due to the mismatch between encoded and decoded URI representations.
The technical implementation of this vulnerability exploits the fundamental mismatch between how URIs are stored and how they are processed within the lighttpd configuration system. When a client requests a resource, the web server examines the requested URI against configured patterns in url.redirect and url.rewrite sections. However, the server performs pattern matching against the raw URI string without first applying URL decoding, which means that encoded characters such as %20 for spaces or %2F for forward slashes remain in their encoded form during comparison. This discrepancy allows attackers to craft requests where the encoded URI matches a pattern, but the decoded version does not, thereby circumventing access restrictions that should have been enforced. The flaw represents a classic case of improper input sanitization and pattern matching, where the server's logic fails to account for the difference between encoded and decoded URI representations.
The operational impact of this vulnerability extends beyond simple access bypass, potentially allowing attackers to gain unauthorized access to restricted resources or modify sensitive data within the web server's protected areas. Since the vulnerability affects core web server functionality through URL redirection and rewriting, it could enable attackers to bypass authentication mechanisms, access restricted directories, or redirect traffic to malicious destinations. The consequences are particularly severe in environments where lighttpd serves sensitive applications or handles confidential data, as the vulnerability could allow privilege escalation or data exfiltration. This type of vulnerability aligns with ATT&CK technique T1071.004 for application layer protocol manipulation and could be leveraged for lateral movement within networks where lighttpd is deployed as part of web infrastructure. The vulnerability's exploitation requires minimal privileges and can be automated, making it particularly dangerous for widespread deployment.
Mitigation strategies for CVE-2008-4359 involve immediate upgrade to lighttpd version 1.4.20 or later, which contains the necessary patches to address the URI comparison issue. Organizations should also implement additional security measures including monitoring for suspicious URI patterns and regular configuration audits to ensure that url.redirect and url.rewrite rules do not create unintended access paths. Network segmentation and firewall rules can provide additional defense in depth, while logging and monitoring should be enhanced to detect unusual access patterns that might indicate exploitation attempts. Security teams should also consider implementing Web Application Firewalls that can detect and block malicious URI patterns before they reach the web server, providing an additional layer of protection against this class of vulnerability. The vulnerability serves as a reminder of the importance of proper URI handling in web applications and the critical need for consistent input validation across all processing stages.