CVE-2026-16386: Firefox WebGPU Information Disclosure Flaw

CVE-2026-16386 Overview

CVE-2026-16386 is an information disclosure vulnerability in the Graphics: WebGPU component of Mozilla Firefox and Thunderbird. The flaw stems from the use of uninitialized memory [CWE-908], allowing a remote attacker to read residual data from memory that was never explicitly cleared before use. Mozilla addressed the issue in Firefox 153 and Thunderbird 153 through advisories MFSA-2026-68 and MFSA-2026-71. The vulnerability is network-reachable through crafted web content that exercises the WebGPU API, requires no user interaction, and needs no privileges to trigger.

Critical Impact
A remote attacker can leverage crafted WebGPU workloads to leak uninitialized process memory from the browser, potentially exposing sensitive data across origin boundaries.

Affected Products

Mozilla Firefox versions prior to 153
Mozilla Thunderbird versions prior to 153
Any downstream distributions bundling vulnerable Gecko builds with WebGPU enabled

Discovery Timeline

2026-07-21 - CVE-2026-16386 published to NVD
2026-07-22 - Last updated in NVD database

Technical Details for CVE-2026-16386

Vulnerability Analysis

The defect resides in the WebGPU implementation inside the Gecko graphics stack. WebGPU exposes GPU compute and rendering primitives to JavaScript running in web content. When the component allocates buffers, textures, or transient staging regions, one or more code paths return memory to the caller without zero-initializing the underlying storage. Content JavaScript can then read the contents of these resources and observe leftover bytes from prior allocations.

Because the browser process handles data from many origins, cookies, tokens, decoded media frames, and internal pointers may reside in reclaimed heap regions. The vulnerability enables cross-origin information leakage and can also assist in defeating address space layout randomization by disclosing pointer values used elsewhere in exploit chains.

Root Cause

The root cause is a violation of the initialization contract described by CWE-908: Use of Uninitialized Resource. GPU resource allocators in the WebGPU code path fail to enforce zero-fill on newly created or recycled buffers before making them observable to script. See Mozilla Bug Report #2041916 for the upstream tracking record.

Attack Vector

Exploitation is remote and unauthenticated. An attacker hosts a malicious page that a victim visits with a vulnerable Firefox build, or delivers HTML email rendered by Thunderbird with remote content enabled. The page issues WebGPU calls to allocate resources, then reads them back via mapped buffers or shader outputs. The returned bytes contain uninitialized memory the attacker exfiltrates through standard fetch or WebSocket channels.

No verified proof-of-concept code has been published. Refer to Mozilla Security Advisory MFSA-2026-68 and Mozilla Security Advisory MFSA-2026-71 for vendor technical detail.

Detection Methods for CVE-2026-16386

Indicators of Compromise

Firefox or Thunderbird processes at versions below 153 loading untrusted web content with WebGPU enabled via dom.webgpu.enabled.
Unexpected outbound POST or WebSocket traffic from browser processes carrying opaque binary payloads after visits to unfamiliar domains.
Web pages that immediately request WebGPU adapters and allocate large numbers of GPUBuffer or GPUTexture resources without a legitimate rendering purpose.

Detection Strategies

Inventory endpoints for firefox.exe, firefox, and thunderbird binaries and correlate reported versions against the fixed 153 release.
Inspect browser telemetry and enterprise policy logs for pages that invoke navigator.gpu.requestAdapter() from low-reputation origins.
Hunt in proxy and DNS logs for repeat visits to newly registered domains coinciding with browser process crashes or memory-region access anomalies.

Monitoring Recommendations

Track browser version compliance continuously through configuration management and flag hosts running Firefox or Thunderbird below 153.
Alert on Mozilla application processes spawning unusual child processes or issuing large volume outbound uploads shortly after page load.
Ingest Mozilla security advisory feeds so future MFSA identifiers referencing the same component surface in the vulnerability management workflow.

How to Mitigate CVE-2026-16386

Immediate Actions Required

Upgrade Firefox to version 153 or later on all managed endpoints.
Upgrade Thunderbird to version 153 or later, including any downstream extended support builds once vendors publish them.
Validate enterprise update channels such as Firefox ESR and distribution package mirrors have picked up the fixed builds.

Patch Information

Mozilla resolved the issue in Firefox 153 and Thunderbird 153. Full remediation guidance is published in Mozilla Security Advisory MFSA-2026-68 and Mozilla Security Advisory MFSA-2026-71. Apply the vendor patch rather than relying on configuration changes as a long-term control.

Workarounds

Disable WebGPU in Firefox by setting dom.webgpu.enabled to false in about:config on hosts that cannot be immediately updated.
Block remote content rendering in Thunderbird and disallow JavaScript in message display where policy permits.
Restrict browser access to untrusted sites through enterprise web filtering until patched builds are deployed fleet-wide.

bash

# Configuration example: enforce WebGPU disable via Firefox enterprise policy
cat > /etc/firefox/policies/policies.json <<'EOF'
{
  "policies": {
    "Preferences": {
      "dom.webgpu.enabled": {
        "Value": false,
        "Status": "locked"
      }
    }
  }
}
EOF