CVE-2015-0255 in X Server
Summary
by MITRE
X.Org Server (aka xserver and xorg-server) before 1.16.3 and 1.17.x before 1.17.1 allows remote attackers to obtain sensitive information from process memory or cause a denial of service (crash) via a crafted string length value in a XkbSetGeometry request.
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Analysis
by VulDB Data Team • 08/29/2025
The vulnerability identified as CVE-2015-0255 affects the X.Org Server implementation of the X Window System, specifically targeting versions prior to 1.16.3 and 1.17.1. This issue resides within the XkbSetGeometry request handling mechanism, which is part of the X Keyboard Extension protocol used for managing keyboard layouts and geometry configurations. The vulnerability represents a critical security flaw that could be exploited by remote attackers to either extract sensitive information from process memory or cause system instability through denial of service conditions.
The technical flaw manifests through improper validation of string length parameters within the XkbSetGeometry request processing. When a maliciously crafted XkbSetGeometry request is sent to the X server, it contains an invalid string length value that bypasses normal input sanitization checks. This allows attackers to manipulate memory access patterns within the xserver process, potentially leading to information disclosure through memory leaks or causing buffer overflows that result in process crashes. The vulnerability stems from inadequate bounds checking and memory management within the keyboard geometry handling code path, creating a condition where attacker-controlled data can influence memory access operations.
From an operational impact perspective, this vulnerability poses significant risks to systems running affected X.Org Server versions, particularly in networked environments where X11 forwarding or remote desktop connections are utilized. Attackers could leverage this flaw to gain unauthorized access to sensitive data stored in process memory, potentially including authentication tokens, user credentials, or other confidential information. The denial of service aspect creates additional operational concerns by allowing attackers to disrupt graphical sessions and potentially cause system instability. This vulnerability affects not only desktop environments but also server configurations that rely on X11 for remote management or graphical user interfaces, making it particularly dangerous in enterprise and cloud computing environments.
Mitigation strategies should prioritize immediate patching of affected X.Org Server installations to versions 1.16.3 or 1.17.1 and later. Organizations should implement network segmentation to limit access to X11 services and disable unnecessary X11 forwarding capabilities where possible. Security monitoring should be enhanced to detect unusual XkbSetGeometry request patterns and potential exploitation attempts. The vulnerability aligns with CWE-125: Out-of-bounds Read and CWE-129: Improper Validation of Array Index, and can be mapped to ATT&CK technique T1059.007: Command and Scripting Interpreter: Python within the context of potential exploitation methods. System administrators should also consider implementing intrusion detection systems that can identify and block malicious X11 protocol requests, particularly those containing suspicious string length values that could trigger the memory access violations described in this vulnerability.