CVE-2026-92013: Firefox CanvasWebGL Privilege Escalation

CVE-2026-92013 Overview

CVE-2026-92013 is a privilege escalation vulnerability caused by incorrect boundary conditions in the Graphics: CanvasWebGL component of Mozilla Firefox and Thunderbird. The flaw is classified as a buffer copy without checking size of input ([CWE-120]). Mozilla addressed the issue in Firefox 156, Firefox ESR 115.41, Firefox ESR 140.16, Firefox ESR 153.3, Thunderbird 156, Thunderbird 140.16, and Thunderbird 153.3. Exploitation requires network reachability to a malicious resource and user interaction, such as visiting a crafted web page or rendering hostile content in Thunderbird.

Critical Impact

A remote attacker can trigger memory corruption in the WebGL rendering pipeline, potentially leading to privilege escalation within the browser process and compromise of confidentiality, integrity, and availability.

Affected Products

• Mozilla Firefox versions prior to 156
• Mozilla Firefox ESR prior to 115.41, 140.16, and 153.3
• Mozilla Thunderbird prior to 156, 140.16, and 153.3

Discovery Timeline

• 2026-09-15 - CVE-2026-92013 published to the National Vulnerability Database
• 2026-09-16 - CVE-2026-92013 last modified in NVD

Technical Details for CVE-2026-92013

Vulnerability Analysis

The vulnerability resides in the CanvasWebGL graphics component, which handles GPU-accelerated 2D and 3D rendering exposed to web content through the <canvas> element and the WebGL JavaScript API. Incorrect boundary conditions allow write or read operations to cross the intended memory region during WebGL processing. Because CanvasWebGL runs within a privileged browser subsystem that interacts with graphics drivers, corruption in this path can be leveraged to escalate privileges beyond the content sandbox. The issue affects Thunderbird as well, since it shares Gecko rendering code with Firefox, though risk in Thunderbird is limited to contexts where scripting or remote content is enabled.

Root Cause

The root cause is a boundary condition error tracked as [CWE-120], buffer copy without checking size of input. The WebGL implementation fails to correctly validate the extents of a buffer during a copy or draw operation, allowing adjacent memory to be read or overwritten. Mozilla resolved the defect in the fixed Firefox, ESR, and Thunderbird releases listed in the advisories. Refer to Mozilla Bug Report #2058078 for the underlying technical discussion.

Attack Vector

Exploitation is network-based and requires user interaction. An attacker hosts a malicious web page that issues a crafted sequence of WebGL calls exercising the vulnerable boundary path. When a victim visits the page in an unpatched Firefox build, or renders equivalent HTML content in an affected Thunderbird build with scripting enabled, the malformed WebGL operation triggers memory corruption. Successful exploitation can elevate privileges out of the rendering process and compromise browser state. See the Mozilla advisories MFSA-2026-90 through MFSA-2026-96 for vendor guidance.

No verified public exploit code is available at this time; the vulnerability is described in prose based on Mozilla's advisories.

Detection Methods for CVE-2026-92013

Indicators of Compromise

• Unexpected crashes or hangs in firefox.exe, plugin-container, or the GPU Process correlated with WebGL-heavy page loads.
• Browser telemetry showing repeated WebGL context loss or driver resets on specific domains.
• Outbound connections from browser child processes to unfamiliar hosts shortly after visiting untrusted pages.

Detection Strategies

• Inventory installed Firefox and Thunderbird versions across managed endpoints and flag any build below the fixed versions listed in the advisories.
• Monitor endpoint logs for browser process crashes with graphics module stack frames, which may indicate exploitation attempts against WebGL.
• Correlate web proxy logs with browser crash events to identify malicious pages that may be targeting the CanvasWebGL path.

Monitoring Recommendations

• Enable crash reporting and forward Firefox and Thunderbird crash telemetry to a centralized log platform for review.
• Alert on child browser processes spawning shells, script interpreters, or performing unusual filesystem writes after visiting external sites.
• Track patch compliance for Firefox and Thunderbird as part of routine vulnerability management scans.

How to Mitigate CVE-2026-92013

Immediate Actions Required

• Upgrade Firefox to version 156 or later on all endpoints.
• Upgrade Firefox ESR to 115.41, 140.16, or 153.3 depending on the deployed ESR track.
• Upgrade Thunderbird to 156, 140.16, or 153.3 depending on the deployed track.
• Restart browsers and mail clients after patching to ensure updated binaries load.

Patch Information

Mozilla published fixes across advisories MFSA-2026-90, MFSA-2026-91, MFSA-2026-92, MFSA-2026-93, MFSA-2026-94, MFSA-2026-95, and MFSA-2026-96. Apply the patched release aligned to your Firefox or Thunderbird channel.

Workarounds

• Disable WebGL where feasible by setting webgl.disabled to true in about:config until patches are deployed.
• In Thunderbird, keep remote content and JavaScript disabled for messages from untrusted senders.
• Restrict browsing to trusted sites via web filtering while patch rollout is in progress.

# Disable WebGL as a temporary workaround in Firefox user.js
echo 'user_pref("webgl.disabled", true);' >> "$HOME/.mozilla/firefox/<profile>/user.js"