CVE-2026-92011: Firefox CanvasWebGL Privilege Escalation

CVE-2026-92011 Overview

CVE-2026-92011 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 user interaction, typically by navigating to an attacker-controlled web page that renders malicious WebGL content.

Critical Impact

A remote attacker can trigger memory corruption in the WebGL rendering path, potentially leading to privilege escalation and full compromise of confidentiality, integrity, and availability on the affected host.

Affected Products

• Mozilla Firefox versions prior to 156, Firefox ESR prior to 115.41, 140.16, and 153.3
• Mozilla Thunderbird versions prior to 156, 140.16, and 153.3
• Any application embedding the vulnerable Gecko CanvasWebGL component

Discovery Timeline

• 2026-09-15 - CVE-2026-92011 published to NVD
• 2026-09-16 - Last updated in NVD database

Technical Details for CVE-2026-92011

Vulnerability Analysis

The vulnerability resides in the CanvasWebGL graphics component that implements WebGL rendering inside the Gecko engine. Incorrect boundary conditions allow operations on graphics buffers to reference memory outside intended limits. This class of flaw, tracked as [CWE-120], produces a buffer overflow condition when the component processes crafted WebGL inputs. The result is memory corruption inside the content or GPU process, which attackers can leverage to break out of expected privilege boundaries in the browser sandbox.

Root Cause

The root cause is a boundary check error in the WebGL rendering path. The affected code fails to correctly validate size parameters before copying or accessing graphics buffer data. When an attacker supplies WebGL calls with edge-case dimensions or offsets, the miscalculation results in out-of-bounds memory access. Mozilla resolved the defect by tightening bounds validation in the fixed releases referenced in the associated Mozilla Foundation Security Advisories (MFSA 2026-90 through MFSA 2026-96).

Attack Vector

Exploitation is network-based and requires user interaction. A victim must load a web page or open HTML email content that invokes the vulnerable WebGL code path. In Firefox, the trigger is a malicious website. In Thunderbird, a message rendering remote HTML can reach the same code path. Successful exploitation corrupts memory in the graphics subsystem and can escalate privileges beyond the content sandbox.

No public proof-of-concept exploit is available. Technical details are documented in the Mozilla Bug Report #2058068 and the Mozilla Security Advisory MFSA 2026-92.

Detection Methods for CVE-2026-92011

Indicators of Compromise

• Unexpected crashes or restarts of firefox.exe, thunderbird.exe, or the associated GPU/content child processes on hosts running vulnerable versions.
• Browser or mail client processes spawning unusual child processes such as command shells or scripting engines after visiting a webpage or rendering HTML mail.
• Outbound connections from Firefox or Thunderbird processes to unfamiliar domains immediately following a WebGL-heavy page render.

Detection Strategies

• Inventory Firefox and Thunderbird installations across the estate and flag any versions below the fixed releases listed in the Mozilla advisories.
• Correlate browser crash telemetry with URL browsing history to identify pages triggering repeated WebGL faults.
• Apply behavioral analytics to identify anomalous process lineage originating from browser or mail client processes.

Monitoring Recommendations

• Ingest endpoint process, network, and crash telemetry into a centralized data lake for cross-source correlation.
• Monitor for exploitation patterns tied to browser sandbox escapes, including token manipulation and injection into higher-privilege processes.
• Alert on execution of LOLBins spawned by firefox.exe or thunderbird.exe.

How to Mitigate CVE-2026-92011

Immediate Actions Required

• Upgrade Firefox to version 156 or later, and update ESR channels to 115.41, 140.16, or 153.3 as appropriate.
• Upgrade Thunderbird to version 156, 140.16, or 153.3 depending on the deployed branch.
• Restart all browser and mail client instances after patch deployment to ensure vulnerable processes are terminated.
• Prioritize patching on workstations used for general web browsing and email handling.

Patch Information

Mozilla released fixes in Firefox 156, Firefox ESR 115.41, Firefox ESR 140.16, Firefox ESR 153.3, Thunderbird 156, Thunderbird 140.16, and Thunderbird 153.3. Refer to the Mozilla Security Advisory MFSA 2026-92 and related advisories MFSA 2026-90 through MFSA 2026-96 for version-specific fix mappings.

Workarounds

• Disable WebGL in Firefox by setting webgl.disabled to true in about:config where WebGL is not required by business applications.
• Configure Thunderbird to render messages in plain text and block remote content to reduce the attack surface for HTML-borne exploitation.
• Enforce enterprise browser policies that restrict access to untrusted sites until patching completes.

# Firefox enterprise policy example to disable WebGL until patched
# /etc/firefox/policies/policies.json
{
  "policies": {
    "Preferences": {
      "webgl.disabled": {
        "Value": true,
        "Status": "locked"
      }
    }
  }
}