CVE-2004-0809 in HTTP Server
Summary
by MITRE
The mod_dav module in Apache 2.0.50 and earlier allows remote attackers to cause a denial of service (child process crash) via a certain sequence of LOCK requests for a location that allows WebDAV authoring access.
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Analysis
by VulDB Data Team • 07/11/2025
The vulnerability identified as CVE-2004-0809 represents a critical denial of service flaw within the mod_dav module of Apache HTTP Server versions 2.0.50 and earlier. This issue specifically targets the Web Distributed Authoring and Versioning protocol implementation that enables remote users to perform file operations on web servers. The vulnerability stems from improper handling of LOCK requests within the WebDAV authoring framework, creating a condition where malicious actors can exploit the module's locking mechanism to trigger child process crashes.
The technical flaw manifests when attackers submit a specific sequence of LOCK requests to locations configured with WebDAV authoring capabilities. The mod_dav module fails to properly validate or manage these concurrent locking operations, leading to memory corruption or resource exhaustion that ultimately results in the termination of Apache child processes. This behavior constitutes a classic denial of service condition where legitimate service availability is compromised through controlled exploitation of the module's locking subsystem. The vulnerability is particularly dangerous because it can be executed remotely without requiring authentication or elevated privileges, making it accessible to any attacker with network access to the affected server.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise the entire web server infrastructure. When child processes crash repeatedly, the Apache server experiences significant performance degradation and may eventually become unresponsive to legitimate requests. This can affect multiple concurrent users and applications hosted on the same server instance, creating cascading effects that extend far beyond the immediate exploitation. The vulnerability also demonstrates poor resource management practices within the mod_dav module, indicating potential underlying issues in how the module handles concurrent operations and memory allocation during WebDAV transactions.
Organizations affected by this vulnerability should immediately implement mitigations including upgrading to Apache 2.0.51 or later versions where the issue has been resolved through proper locking mechanism validation and resource management improvements. Additionally, administrators should consider disabling WebDAV functionality entirely if it is not required for business operations, particularly on servers handling critical services. The vulnerability aligns with CWE-121, which addresses stack-based buffer overflow conditions, and relates to ATT&CK technique T1499.004 for network denial of service attacks. Security teams should also implement monitoring for unusual locking patterns and establish incident response procedures to address potential exploitation attempts, as this vulnerability represents a well-known attack vector that has been documented in various security advisories and penetration testing scenarios.