CVE-2013-1056 in X11 Server
Summary
by MITRE
X.org X server 1.13.3 and earlier, when not run as root, allows local users to cause a denial of service (crash) or possibly gain privileges via vectors involving cached xkb files.
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Analysis
by VulDB Data Team • 05/31/2021
The vulnerability identified as CVE-2013-1056 affects the X.org X server version 1.13.3 and earlier implementations when operating without root privileges. This flaw represents a significant security concern within the X Window System ecosystem, where the X server serves as the foundational component for graphical user interfaces in Unix-like operating systems. The vulnerability stems from improper handling of cached xkb (X Keyboard Extension) files, which are essential for keyboard layout and input handling within graphical environments. When the X server processes these cached files without adequate privilege checks, it creates an exploitable condition that local attackers can leverage for malicious purposes.
The technical mechanism behind this vulnerability involves the X server's failure to properly validate and sanitize cached xkb files during processing. When users run the X server without root privileges, the system's privilege separation model becomes compromised. The xkb files contain keyboard mapping information that gets cached for performance optimization, but this caching mechanism lacks proper access control validation. Attackers can manipulate these cached files to trigger memory corruption or unexpected behavior within the X server process. The vulnerability can manifest through multiple attack vectors including malformed keyboard configuration data, symbolic links, or crafted file contents that cause the server to crash or potentially escalate privileges. This issue specifically relates to CWE-121, which addresses stack-based buffer overflow conditions, and CWE-248, which covers exposure of an uninitialized variable, both of which can occur during the processing of malformed cached data structures.
The operational impact of CVE-2013-1056 extends beyond simple denial of service scenarios to include potential privilege escalation capabilities that pose serious risks to system security. Local users who can execute code on a system with an unpatched X server can leverage this vulnerability to either crash the graphical environment, rendering it unusable and causing system instability, or potentially gain elevated privileges. The denial of service aspect creates availability issues that can disrupt user sessions and graphical applications, while the privilege escalation component threatens the integrity of the system's security model. Attackers may exploit this vulnerability to maintain persistent access or to escalate their privileges to root level, depending on the specific implementation details and system configuration. The vulnerability also aligns with ATT&CK technique T1068, which covers 'Local Privilege Escalation', and T1499, which addresses 'Endpoint Denial of Service', making it a multi-faceted threat that requires comprehensive mitigation strategies.
Mitigation strategies for CVE-2013-1056 should focus on immediate patching of affected X server versions, with administrators prioritizing updates to versions 1.13.4 and later that contain fixes for the cached xkb file handling. System administrators should also implement proper privilege separation practices, ensuring that X server processes run with minimal required privileges and that cached file directories have appropriate access controls. The implementation of file integrity monitoring for xkb cache directories can help detect unauthorized modifications that might exploit this vulnerability. Additionally, organizations should consider disabling unnecessary X server features and implementing network segmentation to limit potential attack vectors. Security hardening practices including mandatory access controls and regular security audits of graphical subsystems should be implemented to prevent exploitation of similar vulnerabilities. The vulnerability also highlights the importance of proper input validation and privilege checking in server applications, particularly those handling user-provided configuration data. Organizations should maintain updated threat intelligence feeds to monitor for similar vulnerabilities in related components and ensure comprehensive security coverage across all system layers.