CVE-2026-109719: Firefox CanvasWebGL Race Condition Flaw

CVE-2026-109719 Overview

CVE-2026-109719 is a race condition that leads to a use-after-free vulnerability in the Graphics: CanvasWebGL component of Mozilla Firefox and Thunderbird. The flaw affects browsers and mail clients that render untrusted WebGL content from the network. An attacker who convinces a user to visit a crafted page can trigger concurrent access to freed graphics memory, resulting in memory corruption. Mozilla fixed the issue in Firefox 158, Firefox ESR 115.43, Firefox ESR 153.5, Thunderbird 158, and Thunderbird 153.5. The vulnerability is classified under CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization).

Critical Impact
Successful exploitation can corrupt browser memory through a use-after-free condition in WebGL rendering, potentially leading to limited confidentiality and integrity impact on the client system.

Affected Products

Mozilla Firefox versions prior to 158
Mozilla Firefox ESR versions prior to 115.43 and 153.5
Mozilla Thunderbird versions prior to 158 and 153.5

Discovery Timeline

2026-10-13 - CVE-2026-109719 published to NVD
2026-10-13 - Last updated in NVD database

Technical Details for CVE-2026-109719

Vulnerability Analysis

The vulnerability resides in the Graphics: CanvasWebGL component, which implements the WebGL rendering pipeline for HTML <canvas> elements. WebGL operations execute across multiple threads to accelerate GPU-bound rendering tasks. The flaw stems from unsynchronized access to a shared graphics object across these execution contexts.

When one thread releases a WebGL resource while another thread still holds a reference, the second thread accesses memory that has already been freed. This use-after-free condition can corrupt the browser heap and influence subsequent allocations. The attack requires user interaction, specifically loading a malicious page that drives WebGL calls in a way that reliably wins the race window.

Exploitation complexity is high because an attacker must align the timing of the freeing and reuse operations. However, repeated attempts in a long-lived browser session can increase success probability.

Root Cause

The root cause is improper synchronization [CWE-362] between concurrent operations on a shared CanvasWebGL resource. The component does not enforce consistent locking or lifetime guarantees before dereferencing the object across threads.

Attack Vector

An attacker hosts a malicious web page containing crafted JavaScript and WebGL shader or draw-call sequences. When a victim visits the page in a vulnerable Firefox or Thunderbird build with remote content enabled, the browser triggers the race condition during WebGL processing. No credentials or elevated privileges are required.

No verified public proof-of-concept code is available. Technical specifics are maintained in the Mozilla Bug Report #2073969 and the related Mozilla Foundation Security Advisories.

Detection Methods for CVE-2026-109719

Indicators of Compromise

Unexpected Firefox or Thunderbird process crashes with heap corruption signatures during WebGL rendering
Outbound connections from browser or mail client processes to recently registered or low-reputation domains hosting WebGL content
Browser crash telemetry referencing the CanvasWebGL component or GPU process

Detection Strategies

Inventory installed Firefox and Thunderbird versions across endpoints and flag any build older than the fixed releases listed by Mozilla.
Monitor endpoint telemetry for anomalous child-process behavior spawned by firefox.exe or thunderbird.exe, especially post-crash activity.
Correlate browser crash reports with user web history to identify suspicious WebGL-heavy sites immediately preceding the crash.

Monitoring Recommendations

Enable centralized collection of browser crash dumps and forward them to a SIEM or data lake for pattern analysis.
Alert on repeated GPU process or content process crashes on the same host within short time windows.
Track execution of unexpected binaries or scripts following a browser crash to detect post-exploitation activity.

How to Mitigate CVE-2026-109719

Immediate Actions Required

Upgrade Firefox to version 158 or later and Firefox ESR to 115.43 or 153.5 across all managed endpoints.
Upgrade Thunderbird to version 158 or 153.5 on workstations where remote content rendering is enabled.
Verify auto-update is enforced via group policy or configuration management to prevent regression to vulnerable builds.

Patch Information

Mozilla released fixes in Firefox 158, Firefox ESR 115.43, Firefox ESR 153.5, Thunderbird 158, and Thunderbird 153.5. Refer to the Mozilla advisories for component-level details: MFSA-2026-106, MFSA-2026-107, MFSA-2026-108, MFSA-2026-109, and MFSA-2026-110.

Workarounds

Disable WebGL in Firefox by setting webgl.disabled to true in about:config on hosts that cannot be patched immediately.
In Thunderbird, keep the default policy of blocking remote content in messages to reduce exposure to attacker-controlled WebGL payloads.
Restrict browsing to trusted domains using enterprise web filtering until the patched browser version is deployed.

bash

# Configuration example: disable WebGL via Firefox enterprise policy (policies.json)
{
  "policies": {
    "Preferences": {
      "webgl.disabled": {
        "Value": true,
        "Status": "locked"
      }
    }
  }
}