CVE-2001-1086 in X11
Summary
by MITRE
XDM in XFree86 3.3 and 3.3.3 generates easily guessable cookies using gettimeofday() when compiled with the HasXdmXauth option, which allows remote attackers to gain unauthorized access to the X display via a brute force attack.
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Analysis
by VulDB Data Team • 01/23/2025
The vulnerability described in CVE-2001-1086 represents a critical security flaw in the X Display Manager XDM component of XFree86 versions 3.3 and 3.3.3. This issue specifically affects systems that are compiled with the HasXdmXauth option, creating a significant weakness in the authentication mechanism that protects X Window System displays. The X Window System, commonly known as X11, serves as the foundation for graphical user interfaces in Unix-like operating systems, making this vulnerability particularly concerning as it directly impacts the security of graphical desktop environments. The flaw stems from the predictable nature of cookie generation, which forms the basis for authenticating access to X displays, thereby compromising the integrity of the entire graphical session management system.
The technical root cause of this vulnerability lies in the use of gettimeofday() function for generating authentication cookies within XDM. This approach produces cookies that are easily guessable due to the predictable nature of timestamp-based entropy. When XDM generates authentication cookies using gettimeofday(), the resulting values contain sufficient temporal information that enables attackers to perform brute force attacks with relatively low computational overhead. The weakness directly maps to CWE-330, which describes the use of insufficiently random values, and more specifically aligns with CWE-331, which addresses insufficient entropy in random number generation. The predictable cookie generation means that an attacker can systematically guess valid authentication tokens without requiring extensive computational resources or sophisticated techniques, making this attack vector particularly accessible to adversaries with minimal technical expertise.
The operational impact of this vulnerability extends far beyond simple unauthorized access, as it fundamentally undermines the security model of X Window System implementations. Remote attackers can exploit this weakness to gain unauthorized access to graphical displays, potentially leading to complete system compromise when combined with other attack vectors. The vulnerability affects systems where XDM is actively running and managing display access, which includes most Unix-like systems with graphical interfaces such as Linux distributions, Solaris, and various BSD implementations. This weakness enables attackers to perform session hijacking, execute arbitrary commands with graphical privileges, and potentially escalate their access to gain deeper system control. The attack can be executed from any remote location without requiring physical access to the target system, making it particularly dangerous in networked environments where XDM services are exposed to external networks.
Mitigation strategies for this vulnerability should focus on immediate patch application and system hardening measures. The primary solution involves upgrading to XFree86 versions that address this specific cookie generation issue, typically those released after the vulnerability disclosure. System administrators should also implement network segmentation to limit access to XDM services, ensuring that these services are not exposed to untrusted networks. Additional protective measures include configuring XDM to use stronger random number generators for cookie creation, implementing proper firewall rules to restrict access to XDM ports, and monitoring for suspicious authentication attempts. From an ATT&CK perspective, this vulnerability relates to T1078.002 which covers valid accounts and T1562.001 which involves defense evasion through authentication bypass techniques. Organizations should also consider implementing intrusion detection systems to monitor for brute force attack patterns and establish proper logging mechanisms to track authentication attempts and potential exploitation attempts against XDM services.