CVE-2026-16393: Firefox WebGPU Buffer Overflow Vulnerability

CVE-2026-16393 Overview

CVE-2026-16393 is a boundary condition flaw in the Graphics: WebGPU component used by Mozilla Firefox and Thunderbird. The vulnerability falls under [CWE-119], improper restriction of operations within the bounds of a memory buffer. Remote attackers can trigger the flaw over the network without authentication or user interaction. Mozilla addressed the issue in Firefox 153 and Thunderbird 153. Public references include Mozilla Bug Report #2045410, Mozilla Security Advisory MFSA-2026-68, and Mozilla Security Advisory MFSA-2026-71.

Critical Impact
A remote attacker can exploit incorrect boundary conditions in WebGPU to access sensitive memory contents or crash the browser, affecting confidentiality and availability.

Affected Products

Mozilla Firefox versions prior to 153
Mozilla Thunderbird versions prior to 153
WebGPU graphics component within the Gecko engine

Discovery Timeline

2026-07-21 - CVE-2026-16393 published to NVD
2026-07-22 - Last updated in NVD database

Technical Details for CVE-2026-16393

Vulnerability Analysis

The vulnerability resides in the WebGPU implementation inside the Firefox Graphics stack. WebGPU exposes GPU compute and rendering primitives to web content through JavaScript APIs. The component fails to correctly validate boundary conditions on buffer or resource operations, allowing out-of-bounds memory access. The flaw is network-reachable through a malicious web page, requires no privileges, and no user interaction beyond visiting the attacker-controlled content. Successful exploitation impacts confidentiality and availability, consistent with disclosure of process memory and browser crashes. Thunderbird is affected because it embeds the same Gecko rendering engine.

Root Cause

The root cause is improper restriction of operations within the bounds of a memory buffer inside WebGPU code paths. Incorrect boundary checks allow calculations to reference memory outside the intended allocation. This class of defect [CWE-119] often results from mismatched size units, incorrect signed and unsigned arithmetic, or missing validation of attacker-influenced offsets and lengths. Consult the Mozilla Bug Report #2045410 for implementation-level detail.

Attack Vector

An attacker hosts a crafted web page that invokes WebGPU APIs with parameters designed to trigger the boundary error. When a victim loads the page in a vulnerable Firefox build, the browser executes the malicious GPU workload and accesses memory outside intended limits. Thunderbird users can be reached through content rendered in message previews when scripting or remote content is permitted. See the technical description in Mozilla Security Advisory MFSA-2026-68.

No verified proof-of-concept code is publicly available. Refer to the Mozilla
Bug Report #2045410 and MFSA-2026-68 for implementation-level information once
Mozilla lifts access restrictions on the bug entry.

Detection Methods for CVE-2026-16393

Indicators of Compromise

Firefox or Thunderbird process crashes referencing WebGPU modules such as wgpu or webgpu in crash reports
Browser telemetry showing repeated GPU process restarts after loading untrusted pages
Endpoint logs recording Firefox or Thunderbird versions below 153 still active in the environment

Detection Strategies

Inventory installed Firefox and Thunderbird versions across managed endpoints and flag builds earlier than 153
Alert on outbound connections from browsers to newly registered or low-reputation domains that serve WebGPU content
Correlate browser crash events with proximate web navigation events to identify targeted exploitation attempts

Monitoring Recommendations

Ingest browser crash telemetry and endpoint process telemetry into a centralized analytics platform for version and stability tracking
Monitor GPU sandbox and content process termination events on user workstations
Track patch compliance rates for Mozilla applications and enforce thresholds through configuration management

How to Mitigate CVE-2026-16393

Immediate Actions Required

Update Mozilla Firefox to version 153 or later on all managed endpoints
Update Mozilla Thunderbird to version 153 or later, including workstations and shared mail hosts
Restart affected applications after patching to ensure vulnerable processes are no longer resident
Verify enterprise policies do not pin browsers to older release channels

Patch Information

Mozilla fixed the vulnerability in Firefox 153 and Thunderbird 153. Administrators should deploy the vendor-supplied builds referenced in Mozilla Security Advisory MFSA-2026-68 and Mozilla Security Advisory MFSA-2026-71. Enterprise deployments using the Extended Support Release channel should confirm the corresponding ESR build includes the fix before assuming remediation.

Workarounds

Disable WebGPU in Firefox by setting dom.webgpu.enabled to false in about:config until patching is complete
Restrict Thunderbird from loading remote content and scripting in messages through mail policy settings
Apply browser isolation or restrict WebGPU capable sites through enterprise URL filtering where updates cannot be applied immediately

bash

# Firefox enterprise policy to disable WebGPU pending patch deployment
# policies.json
{
  "policies": {
    "Preferences": {
      "dom.webgpu.enabled": {
        "Value": false,
        "Status": "locked"
      }
    }
  }
}