Mesa WebGPU Out-of-Bounds Write Vulnerability (CVE-2026-40393)

CVE-2026-40393 is a critical vulnerability affecting Mesa, an open-source graphics library, specifically impacting the WebGPU component. The vulnerability stems from insufficient validation of the amount of data to be allocated, allowing an attacker to influence the allocation size via an untrusted party. This value is subsequently passed to the alloca function, resulting in a heap out-of-bounds write. The vulnerability affects Mesa versions prior to 25.3.6 and 26 prior to 26.0.1. Successful exploitation could allow for arbitrary code execution within the context of the application using the vulnerable Mesa library. This is a significant concern for systems utilizing Mesa for WebGPU rendering, including potentially web browsers and other graphics-intensive applications.

Attack Chain

1. An attacker provides a malicious WebGPU input that influences the size of a data allocation.
2. The application using the vulnerable Mesa library processes the malicious WebGPU input.
3. The size parameter, controlled (at least partially) by the attacker, is passed to the alloca function within the WebGPU component of Mesa.
4. alloca allocates a buffer on the stack based on the attacker-controlled size.
5. Due to missing or insufficient validation, the allocated buffer size is smaller than the actual data being written.
6. A write operation occurs to this buffer, exceeding its boundaries (out-of-bounds write).
7. The out-of-bounds write corrupts adjacent memory regions on the stack, potentially overwriting critical data or return addresses.
8. The corrupted memory leads to application crash or, in more sophisticated attacks, allows the attacker to hijack program control and execute arbitrary code.

Impact

Successful exploitation of CVE-2026-40393 can lead to arbitrary code execution within the context of the application using the vulnerable Mesa library. This could allow an attacker to gain control of the affected system, potentially leading to data theft, system compromise, or denial-of-service. Given the wide usage of Mesa in Linux systems and potentially other platforms for graphics rendering, the impact could be significant if exploited widely.

Recommendation

• Upgrade Mesa to version 25.3.6 or later, or version 26.0.1 or later to patch CVE-2026-40393.
• Monitor web server logs for suspicious requests containing unusual WebGPU commands as a proactive measure (see example rule below).
• Implement input validation on applications that use the Mesa library to ensure that data passed to the WebGPU component is within expected bounds.