CVE-2026-94283 in libX11
Summary
by MITRE • 09/28/2026
An out-of-bounds read vulnerability in libX11's XIM (X Input Method) attribute parser in libX11 before 1.8.14 could be used by malicious X servers to crash attached X clients.
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Analysis
by VulDB Data Team • 09/28/2026
The vulnerability identified within the libX11 library, specifically affecting versions prior to 1.8.14, centers on a critical flaw in the implementation of the X Input Method attribute parser. This component is responsible for processing input method protocols that facilitate text entry and localization support across graphical user interfaces. The core technical deficiency lies in an out-of-bounds read condition triggered during the parsing of specific attributes within the XIM protocol stream. When a malicious or compromised X server sends crafted data containing malformed or excessively long attribute values, the parser fails to perform adequate bounds checking before accessing memory locations associated with these attributes. This lack of validation allows the application to read from memory addresses that lie outside the allocated buffer boundaries, leading to an invalid memory access event.
From an operational perspective, this vulnerability poses a significant risk to system stability and availability. Because libX11 is foundational to most Linux-based graphical environments, any client application relying on it for input handling becomes susceptible to exploitation. The immediate consequence of triggering this out-of-bounds read is typically the termination of the affected X client process due to a segmentation fault or similar memory protection violation. While the primary impact observed in initial reports is denial of service through application crashes, such memory corruption vulnerabilities can sometimes be leveraged for more severe outcomes depending on the specific execution context and compiler protections enabled at build time. An attacker controlling the input stream from an X server could potentially use this flaw to disrupt user workflows or cause instability within multi-window environments where multiple clients are active simultaneously.
This vulnerability aligns with Common Weakness Enumeration category CWE-125, which describes out-of-bounds read vulnerabilities that allow attackers to access memory beyond allocated boundaries. In the context of the MITRE ATT&CK framework, this flaw facilitates techniques related to execution disruption and potentially information disclosure if sensitive data residing in adjacent memory regions is exposed through the erroneous reads. The attack vector requires interaction with a malicious X server, which implies that an attacker must have some level of control over or influence on the display server environment where the victim application operates. This could occur in shared computing environments, virtualized desktop infrastructure, or scenarios where users connect to untrusted remote displays using protocols like VNC or RDP that rely on libX11 for rendering and input processing.
Mitigation strategies primarily involve updating the libX11 library to version 1.8.14 or later, which includes patches addressing this specific parsing logic error. System administrators should prioritize patching desktop environments and applications linked against vulnerable versions of libX11 to restore integrity and availability guarantees. Additionally, deploying runtime security mechanisms such as Address Space Layout Randomization (ASLR) can help mitigate the potential impact by making it more difficult for attackers to predict memory layouts if exploitation attempts are made beyond simple denial-of-service scenarios. Users should also exercise caution when connecting to untrusted X servers or remote display services until all client-side components are verified to be running patched versions of the library, thereby reducing the attack surface available to adversaries seeking to disrupt graphical sessions through protocol-level abuse.