CVE-2017-13723 in X.Org Server
Summary
by MITRE
In X.Org Server (aka xserver and xorg-server) before 1.19.4, a local attacker authenticated to the X server could overflow a global buffer, causing crashes of the X server or potentially other problems by injecting large or malformed XKB related atoms and accessing them via xkbcomp.
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Analysis
by VulDB Data Team • 08/29/2025
The vulnerability identified as CVE-2017-13723 represents a critical buffer overflow flaw within the X.Org Server component known as xserver or xorg-server. This issue affects versions prior to 1.19.4 and stems from insufficient input validation mechanisms when processing XKB (X Keyboard Extension) related atoms. The flaw exists in the global buffer management system where the server fails to properly bounds-check data structures when handling keyboard extension information, creating an exploitable condition that can be leveraged by authenticated local users.
The technical implementation of this vulnerability involves the manipulation of XKB atoms through the xkbcomp utility, which serves as a command-line tool for compiling XKB keyboard descriptions. When a local attacker authenticates to the X server and injects large or malformed XKB related atoms, the server's global buffer handling mechanism becomes compromised. This buffer overflow occurs because the system does not adequately validate the size of incoming atom data before copying it into fixed-size global buffers, allowing malicious input to exceed allocated memory boundaries.
From an operational perspective, this vulnerability presents significant risks to system stability and security integrity. The primary impact manifests as potential crashes of the X server itself, which can result in denial of service conditions affecting graphical user interfaces and desktop environments. However, the implications extend beyond simple crashes, as buffer overflows of this nature often provide pathways for more sophisticated exploitation techniques. The vulnerability allows for arbitrary code execution or privilege escalation within the context of the X server process, potentially enabling attackers to gain elevated system privileges.
The vulnerability maps directly to CWE-121, which describes "Stack-based Buffer Overflow" and CWE-122, which addresses "Heap-based Buffer Overflow" in the context of improper input validation and memory management. According to MITRE ATT&CK framework, this represents a technique for privilege escalation and defense evasion through local exploitation of system components. The attack vector requires local authentication to the X server, making it a significant concern for multi-user systems where users may have legitimate access to graphical interfaces but could leverage this vulnerability for malicious purposes.
Effective mitigation strategies for CVE-2017-13723 require immediate patching of affected X.Org Server installations to version 1.19.4 or later. System administrators should implement comprehensive monitoring of X server processes for unusual behavior or crash patterns that might indicate exploitation attempts. Additionally, access controls should be enforced to limit local authentication to the X server, particularly in multi-user environments where unauthorized access could enable exploitation. The implementation of privilege separation mechanisms and regular security audits of graphical server components can further reduce the attack surface and prevent unauthorized manipulation of XKB atom data structures.