External risk intelligence

Mesa WebGPU Out-of-Bounds Memory Access Vulnerability.

CVE advisorySeverity: CRITICAL (CVSS 9.8)

CVE-2026-40393

Mesa is a graphics library that runs locally within the user's software stack to facilitate hardware-accelerated rendering. While it processes untrusted content (like WebGPU shaders) via browser or application interaction, it is a client-side component integrated into local applications, not a network-facing service, appliance, or gateway accessible from the internet.

Out-of-bounds Write

Mesa3d Mesa

before 25.3.626.0.0

Halo Surface Signal: 1 out of 5 — much less likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

This advisory concerns a critical vulnerability in the Mesa graphics library, specifically within its WebGPU implementation. The issue stems from how the library handles memory allocation based on untrusted input, potentially leading to memory access errors. This could have implications for systems utilizing this graphics processing software. The primary concern is to confirm if your environment is affected and to understand the potential exposure.

Memory errors in graphics processing.
Matters for systems using graphics acceleration.
Confirm relevance and potential exposure.

Attack Path

How an attacker could exploit the issue

An attacker could potentially exploit this vulnerability by sending specially crafted data to a vulnerable application that utilizes the WebGPU feature. This could lead to an out-of-bounds memory access, allowing the attacker to read or write to memory they should not have access to, potentially resulting in system compromise.

Vulnerable component exposed to the internet.
Untrusted data triggers memory error.
Allows arbitrary memory read/write.

Live Threat

Current exploitation, exposure, and threat context

This vulnerability could affect system stability and potentially allow an attacker to cause denial-of-service conditions when WebGPU is used with untrusted input. The out-of-bounds memory access occurs because the amount of memory to be allocated is based on untrusted data.

System stability and service availability.
Untrusted input to WebGPU.
Denial-of-service conditions.

Operational Fix

Recommended remediation, mitigation, and detection steps

This vulnerability in Mesa affects graphics rendering, impacting applications that utilize WebGPU. The first practical step is for infrastructure or platform teams to identify all instances of the affected Mesa versions, confirm their exposure to untrusted input, and determine business criticality. Coordination with application owners and potentially vendor management is necessary to prioritize and plan remediation, considering the operational impact and available maintenance windows.

Own by infrastructure or platform teams.
Verify WebGPU usage and reachability.
Plan remediation based on risk.

Supplementary metadata

CVSS vector

Validate whether this threat affects your internet-facing exposure.

Halo Threat Intelligence helps prioritize remediation with Halo Surface Signal and H/A/L/O context. Start exposure validation with a free external attack surface trial.

Free EASM Trial See How Signal Works

Frequently asked questions

What is Mesa and why does it matter for software?

Mesa is an open-source graphics library that provides hardware-accelerated rendering for applications. It acts as a translation layer, allowing software to talk to your computer's graphics hardware (GPU). It is widely used in Linux environments to power desktop interfaces, browser rendering, and gaming applications. Because it handles complex visual data, it must be highly reliable to ensure system stability and performance.

What does CVE-2026-40393 mean for memory safety?

This vulnerability is an out-of-bounds memory access error, classified as CWE-787. It occurs when a program writes data past the end of an allocated memory buffer. In this case, the Mesa WebGPU implementation trusts data provided by an external source to determine how much memory to allocate. If that input is malicious, it can cause the library to overwrite adjacent memory, which may lead to unauthorized data access or system crashes.

How is the out-of-bounds memory access triggered?

The flaw is triggered when the WebGPU component processes specially crafted, untrusted data that causes an incorrect memory allocation request. Simply having an older version of Mesa installed does not trigger the bug; it requires an application to actively use WebGPU features to process malicious input. If an application does not utilize the WebGPU functionality within Mesa, or if the input is generated by a trusted source, the conditions for this specific memory error are not met.

Is my system at risk according to Halo Surface Signal?

Halo Surface Signal indicates it is very unlikely that Mesa acts as a direct network-facing service. Because Mesa functions as a client-side library integrated into local applications, it does not typically listen for connections from the internet like a web server or gateway. However, you should still evaluate if your local applications accept untrusted content—such as complex shaders or web graphics—which could indirectly expose the library to malicious data.

What is the first step to address this CVE?

Begin by auditing your environment to locate all software versions using Mesa, focusing on those supporting WebGPU features. Verify which of these applications process untrusted content from the web or other external sources. Once identified, consult your operating system or distribution maintainers to find stable updates to versions 25.3.6, 26.0.1, or later, and prioritize patching based on the criticality of the applications using the graphics stack.

References

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.