CVE-2007-3949 in lighttpd
Summary
by MITRE
mod_access.c in lighttpd 1.4.15 ignores trailing / (slash) characters in the URL, which allows remote attackers to bypass url.access-deny settings.
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Analysis
by VulDB Data Team • 07/21/2021
The vulnerability identified as CVE-2007-3949 affects lighttpd version 1.4.15 and stems from a flaw in the mod_access.c module where the web server fails to properly normalize URL paths by ignoring trailing slash characters. This behavior creates a path traversal condition that can be exploited by remote attackers to circumvent access control mechanisms configured through url.access-deny directives. The issue arises from the server's insufficient handling of URL normalization, specifically when processing paths that contain trailing slashes that should logically be equivalent to their non-trailing slash counterparts.
This technical flaw represents a path normalization issue that falls under CWE-174, which deals with the weakness of insufficient canonicalization of path names. The vulnerability allows attackers to craft malicious URLs that bypass intended access restrictions by exploiting the inconsistent handling of trailing slashes in URL parsing. When an administrator configures access controls to deny access to certain paths, the server's failure to normalize the URL path means that both /path and /path/ may be treated as different entities, creating an exploitable gap in the security model. The flaw essentially allows an attacker to append or remove trailing slashes from URLs and potentially gain access to resources that should be restricted.
The operational impact of this vulnerability extends beyond simple access control bypass as it undermines the fundamental security assumptions of web server configuration. Attackers can exploit this weakness to access restricted directories, files, or application endpoints that are protected by url.access-deny rules, potentially leading to unauthorized data access, information disclosure, or further exploitation of the web server. The vulnerability is particularly concerning because it operates at the URL parsing level, meaning it can be exploited across various types of access control configurations without requiring additional attack vectors. This weakness enables attackers to systematically bypass security controls that should prevent access to sensitive areas of the web server's filesystem or application logic.
From a defensive perspective, administrators should immediately upgrade to lighttpd versions that have addressed this path normalization issue, as the vulnerability was resolved in subsequent releases. The mitigation strategy involves ensuring that all web server instances properly canonicalize URLs before applying access control rules, which aligns with ATT&CK technique T1071.004 for application layer protocol manipulation. Organizations should also implement comprehensive URL normalization policies and regularly audit their access control configurations to ensure that trailing slash variations do not create security gaps. Additionally, security monitoring should include detection of unusual URL patterns that might indicate exploitation attempts, particularly when trailing slashes are used in conjunction with access control bypass attempts. The vulnerability demonstrates the critical importance of proper input validation and canonicalization in web server security implementations, as even seemingly minor parsing inconsistencies can create significant security weaknesses that can be systematically exploited by threat actors.