CVE-2000-0491 in X11r6
Summary
by MITRE
Buffer overflow in the XDMCP parsing code of GNOME gdm, KDE kdm, and wdm allows remote attackers to execute arbitrary commands or cause a denial of service via a long FORWARD_QUERY request.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 12/13/2024
The vulnerability described in CVE-2000-0491 represents a critical buffer overflow flaw affecting multiple display manager implementations within the X Window System ecosystem. This vulnerability specifically targets the X Display Manager Control Protocol parsing code used by GNOME gdm, KDE kdm, and wdm display managers, creating a significant security risk for systems relying on these components for graphical user authentication. The flaw manifests when these display managers process specially crafted FORWARD_QUERY requests that exceed the allocated buffer space, leading to potential system compromise or service disruption.
The technical implementation of this vulnerability stems from inadequate input validation within the XDMCP protocol handling code of these display managers. When a maliciously crafted FORWARD_QUERY request is received, the parsing code fails to properly bounds-check the incoming data before copying it into fixed-size buffers. This classic buffer overflow condition allows attackers to overwrite adjacent memory locations, potentially corrupting program execution flow and enabling arbitrary code execution. The vulnerability is particularly dangerous because it operates at the display manager level, which typically runs with elevated privileges and has direct access to system resources and authentication mechanisms.
From an operational perspective, this vulnerability presents a substantial risk to enterprise and organizational security infrastructure since display managers are often exposed to network traffic and may be accessible from untrusted networks. Attackers can exploit this flaw remotely without requiring authentication credentials, making it particularly attractive for initial access or privilege escalation attacks. The potential impact includes complete system compromise through arbitrary code execution, or more commonly, denial of service conditions that prevent legitimate users from accessing graphical login interfaces. This vulnerability directly maps to CWE-121, which describes heap-based buffer overflow conditions, and represents a prime example of how protocol implementation flaws can create persistent security weaknesses in widely deployed software components.
The exploitation of this vulnerability typically involves crafting a specially formatted FORWARD_QUERY packet that exceeds the buffer capacity of the target display manager's parsing code. This approach aligns with ATT&CK technique T1190, which covers the exploitation of remote services through protocol parsing vulnerabilities. Organizations using affected display managers face significant exposure since these components often run as system services and may be accessible from multiple network segments. The vulnerability demonstrates the importance of proper input validation in network-facing applications and highlights how seemingly minor protocol implementation details can create substantial security risks. Security teams should prioritize patching or implementing network-level mitigations to prevent exploitation, as the vulnerability affects core authentication infrastructure components that are fundamental to system security posture.