CVE-2018-14599 in libX11
Summary
by MITRE
An issue was discovered in libX11 through 1.6.5. The function XListExtensions in ListExt.c is vulnerable to an off-by-one error caused by malicious server responses, leading to DoS or possibly unspecified other impact.
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Analysis
by VulDB Data Team • 05/04/2023
The vulnerability identified as CVE-2018-14599 represents a critical security flaw within the X Window System's libX11 library version 1.6.5 and earlier. This issue manifests in the XListExtensions function located within the ListExt.c source file, which serves as a fundamental component for managing X11 extensions within the graphical user interface framework. The flaw arises from inadequate input validation when processing responses from X11 servers, creating a scenario where malicious actors can manipulate server communications to trigger unexpected behavior. The vulnerability specifically exploits an off-by-one error condition that occurs during the processing of extension lists, where buffer boundaries are not properly enforced during memory operations.
The technical implementation of this vulnerability stems from improper boundary checking within the XListExtensions function, which is responsible for enumerating available X11 extensions on a given server connection. When a malicious X11 server responds with carefully crafted extension data that exceeds expected buffer limits, the off-by-one error causes memory corruption that can manifest as program termination or unpredictable system behavior. This type of vulnerability falls under the CWE-129 weakness category, which encompasses issues related to improper validation of the length of input data, particularly in contexts where memory allocation and buffer operations are involved. The flaw operates at the intersection of memory safety and protocol parsing, where the expected data structure does not match the actual data received from the server.
The operational impact of CVE-2018-14599 extends beyond simple denial of service conditions to potentially enable more sophisticated attack vectors within the X11 ecosystem. While the primary effect is a denial of service that can cause applications using libX11 to crash or terminate unexpectedly, the underlying memory corruption vulnerability could theoretically be exploited to achieve arbitrary code execution under specific circumstances. This vulnerability affects any system running X11 applications that rely on libX11 for extension enumeration, including desktop environments, remote desktop clients, and various graphical applications. The attack surface is particularly broad given that X11 remains a fundamental component of Unix-like operating systems and Linux distributions, making this vulnerability relevant across multiple deployment scenarios.
Mitigation strategies for CVE-2018-14599 focus primarily on upgrading to libX11 version 1.6.6 or later, which contains the necessary patches to address the off-by-one error in the XListExtensions function. Security administrators should prioritize patching systems running vulnerable versions of libX11, particularly those in environments where X11 servers might be exposed to untrusted network sources. Additional defensive measures include implementing network segmentation to limit exposure of X11 services to trusted networks only, configuring proper access controls for X11 servers, and monitoring for unusual X11 server responses that might indicate exploitation attempts. From an ATT&CK framework perspective, this vulnerability aligns with techniques related to privilege escalation and denial of service through protocol manipulation, and should be considered when evaluating security controls for graphical user interface components in enterprise environments.