CVE-2003-0548 in GDM
Summary
by MITRE
The X Display Manager Control Protocol (XDMCP) support for GDM before 2.4.1.6 allows attackers to cause a denial of service (daemon crash) when a chosen host expires, a different issue than CVE-2003-0549.
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Analysis
by VulDB Data Team • 09/05/2019
The vulnerability described in CVE-2003-0548 represents a critical denial of service flaw within the X Display Manager Control Protocol implementation of the GNOME Display Manager. This issue affects GDM versions prior to 2.4.1.6 and specifically targets the daemon's handling of host expiration events within the XDMCP framework. The XDMCP protocol serves as a communication mechanism that enables remote display management and authentication, making it a crucial component in graphical user interface environments where remote access is required. The vulnerability manifests when the daemon encounters a situation where a chosen host reaches its expiration time, causing the entire display manager service to crash and become unavailable to legitimate users.
The technical root cause of this vulnerability lies in the improper handling of expired host connections within GDM's XDMCP implementation. When a host connection times out or expires according to the XDMCP protocol specifications, the daemon fails to gracefully manage this event, resulting in an unhandled exception that leads to complete service termination. This flaw falls under the category of improper exception handling and resource management, which are commonly classified under CWE-400 (Uncontrolled Resource Consumption) and CWE-704 (Incorrect Type Conversion or Cast). The daemon's failure to properly validate or process the expiration event creates a condition where malicious actors can trigger the crash by simply initiating a connection that will eventually time out, without requiring any privileged access or complex exploitation techniques.
The operational impact of this vulnerability extends beyond simple service disruption, as it can severely compromise the availability of graphical desktop environments in networked systems. Organizations relying on GDM for remote desktop management, particularly those using XDMCP for authentication and display management, face significant risks when exposed to this vulnerability. The daemon crash results in complete loss of graphical access for users who were connected through the XDMCP protocol, potentially affecting critical business operations that depend on remote desktop services. In enterprise environments, this could lead to productivity losses, service interruptions, and potential security implications if attackers deliberately exploit the vulnerability to deny access to legitimate users. The vulnerability is particularly concerning because it can be triggered without requiring authentication, making it an attractive target for denial of service attacks that can be executed from any network location.
Mitigation strategies for this vulnerability involve immediate patching of affected GDM installations to version 2.4.1.6 or later, which contains the necessary fixes for proper host expiration handling. System administrators should also implement network-level controls to restrict XDMCP access to trusted networks, as recommended in the ATT&CK framework's network ingress prevention tactics. Additional defensive measures include monitoring for unusual connection patterns and implementing automated service restart mechanisms to minimize downtime. Organizations should also consider disabling XDMCP functionality entirely if it is not required for their operations, following the principle of least privilege and reducing the attack surface. The vulnerability demonstrates the importance of proper resource management and exception handling in daemon processes, highlighting that even seemingly simple protocol implementations can contain critical flaws that impact system availability and user access to graphical interfaces.