CVE-2002-1593 in HTTP Server
Summary
by MITRE
mod_dav in Apache before 2.0.42 does not properly handle versioning hooks, which may allow remote attackers to kill a child process via a null dereference and cause a denial of service (CPU consumption) in a preforked multi-processing module.
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Analysis
by VulDB Data Team • 09/03/2025
The vulnerability described in CVE-2002-1593 affects the mod_dav module in Apache HTTP Server versions prior to 2.0.42, representing a critical security flaw that exploits improper handling of versioning hooks within the web server's modular architecture. This issue specifically targets the mod_dav module which provides Web Distributed Authoring and Versioning capabilities, enabling clients to create, move, and manage files on web servers through HTTP methods. The flaw exists in how the module processes versioning operations, creating a condition where maliciously crafted requests can trigger a null pointer dereference during the processing of version control operations.
The technical implementation of this vulnerability stems from inadequate input validation and error handling within the versioning hook mechanisms of mod_dav. When a client submits a specially crafted request that includes malformed versioning information, the module fails to properly validate the incoming data before attempting to dereference pointers associated with version control metadata. This null pointer dereference occurs in the context of Apache's preforked multi-processing module where each child process handles incoming requests, making the exploitation particularly effective for denial of service attacks. The flaw manifests as a condition where the child process crashes or becomes unresponsive, consuming excessive CPU resources and effectively rendering the web server unavailable to legitimate users.
The operational impact of this vulnerability extends beyond simple service disruption, as it represents a sophisticated attack vector that can be exploited by remote attackers without requiring authentication or special privileges. The preforked multi-processing module architecture of Apache means that each child process operates independently, and when one process crashes due to the null dereference, it consumes system resources and may require server restart to restore normal operation. Attackers can repeatedly exploit this vulnerability to maintain sustained denial of service conditions, making it particularly dangerous in production environments where web server availability is critical for business operations.
This vulnerability aligns with CWE-476, which describes NULL Pointer Dereference, and demonstrates how improper error handling can create exploitable conditions in server-side applications. The attack pattern follows ATT&CK technique T1499.004 for Network Denial of Service, where adversaries leverage software vulnerabilities to exhaust system resources and disrupt service availability. Organizations using Apache versions prior to 2.0.42 should immediately implement security patches to address this flaw, as the vulnerability can be exploited remotely and does not require any privileged access to the target system. The recommended mitigation involves upgrading to Apache 2.0.42 or later versions where the mod_dav module properly validates versioning hook data and handles null pointer conditions gracefully, preventing the process termination that leads to denial of service conditions.