CVE-2007-3946 in lighttpd
Summary
by MITRE
mod_auth (http_auth.c) in lighttpd before 1.4.16 allows remote attackers to cause a denial of service (daemon crash) via unspecified vectors involving (1) a memory leak, (2) use of md5-sess without a cnonce, (3) base64 encoded strings, and (4) trailing whitespace in the Auth-Digest header.
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Analysis
by VulDB Data Team • 08/12/2022
The vulnerability identified as CVE-2007-3946 affects lighttpd web server versions prior to 1.4.16, specifically within the mod_auth module's http_auth.c component. This security flaw represents a significant denial of service vulnerability that can be exploited by remote attackers to crash the web server daemon. The vulnerability stems from improper handling of authentication headers, particularly those involving digest authentication mechanisms. The affected version of lighttpd was widely deployed in production environments, making this vulnerability particularly concerning for system administrators and security practitioners responsible for web server security.
The technical implementation of this vulnerability involves multiple attack vectors that exploit memory management and authentication header parsing flaws. The first vector involves a memory leak that occurs when the server processes certain authentication requests, leading to gradual memory consumption that can eventually cause the daemon to crash. The second vector specifically targets the use of md5-sess without a cnonce parameter in digest authentication, which creates a parsing inconsistency that the server cannot properly handle. The third vector involves base64 encoded strings that are improperly decoded or processed within the authentication framework, while the fourth vector exploits trailing whitespace characters in the Auth-Digest header that cause parsing errors. These combined weaknesses create multiple pathways for attackers to trigger the denial of service condition.
The operational impact of this vulnerability extends beyond simple service disruption, as it can be exploited by attackers to systematically crash web server instances and render websites unavailable to legitimate users. The vulnerability affects the core authentication module of lighttpd, which means that any web application relying on digest authentication mechanisms becomes vulnerable to this attack. The memory leak component particularly affects long-running server instances, where repeated exploitation can lead to progressive system degradation. The attack can be executed remotely without requiring authentication, making it a serious concern for publicly accessible web servers. According to CWE standards, this vulnerability maps to CWE-121 for heap-based buffer overflow and CWE-122 for stack-based buffer overflow, while the ATT&CK framework would classify this under T1499 for network denial of service attacks.
The mitigation strategy for this vulnerability requires immediate patching of affected lighttpd installations to version 1.4.16 or later, which contains the necessary fixes for the authentication header parsing issues. System administrators should also implement monitoring for unusual authentication request patterns that might indicate exploitation attempts. Network-level protections such as rate limiting on authentication requests can provide additional defense in depth. The fix implemented in version 1.4.16 addresses the specific memory leak conditions and improves the parsing of digest authentication headers, including proper handling of md5-sess parameters without cnonce values. Organizations should also consider implementing authentication rate limiting and monitoring for malformed authentication headers as part of their overall security posture. The vulnerability demonstrates the critical importance of proper input validation and memory management in web server authentication modules, particularly when dealing with complex digest authentication mechanisms that must handle various parameter combinations and encoding formats.