CVE-2026-12293: Mozilla Firefox Use-After-Free Flaw

CVE-2026-12293 Overview

CVE-2026-12293 is a use-after-free vulnerability in the Graphics: WebGPU component of Mozilla Firefox and Mozilla Thunderbird. The flaw resides in memory management within the WebGPU subsystem, where freed memory can be referenced after deallocation. Mozilla addressed the issue in Firefox 152 and Thunderbird 152. The vulnerability is tracked under [CWE-416] and is exploitable over the network without authentication or user interaction. Successful exploitation can lead to arbitrary code execution within the browser process, with downstream impact on confidentiality, integrity, and availability of the affected host.

Critical Impact
Remote attackers can trigger memory corruption in WebGPU by serving crafted web content, enabling arbitrary code execution in Firefox and Thunderbird without user interaction.

Affected Products

Mozilla Firefox versions prior to 152
Mozilla Thunderbird versions prior to 152
Systems rendering untrusted web content through the WebGPU subsystem

Discovery Timeline

2026-06-16 - CVE-2026-12293 published to NVD
2026-06-17 - Last updated in NVD database
Mozilla Security Advisories - MFSA-2026-57 and MFSA-2026-60 released by Mozilla

Technical Details for CVE-2026-12293

Vulnerability Analysis

The vulnerability is a use-after-free condition (CWE-416) in the WebGPU component of Mozilla's Gecko rendering engine. WebGPU exposes low-level GPU functionality to web content through JavaScript APIs. When the affected code path releases a GPU-related object, a dangling reference remains accessible. Subsequent operations dereference this stale pointer, resulting in memory corruption. Attackers can shape the freed memory region with attacker-controlled data, then trigger the dangling reference to redirect execution flow or corrupt sensitive in-process structures.

Root Cause

The root cause is improper lifetime management of WebGPU objects within the graphics pipeline. Object ownership and reference counting do not consistently track all live references before freeing the underlying allocation. The flaw is reachable from JavaScript executed in any page that the browser renders, including content loaded inside Thunderbird's mail rendering context.

Attack Vector

Exploitation requires a victim to load a malicious page or HTML email that issues crafted WebGPU calls. No privileges and no user interaction beyond loading the content are required. Because Thunderbird shares the Gecko engine, remote HTML content rendered in mail previews exposes the same code path. Refer to Mozilla Bug Report #2039568 for the underlying technical bug tracking.

// No verified public exploit code is available for CVE-2026-12293.
// Refer to Mozilla's advisories and bug tracker for technical details.

Detection Methods for CVE-2026-12293

Indicators of Compromise

Firefox or Thunderbird processes crashing with access violations or segmentation faults referencing WebGPU modules (webgpu, wgpu, dom::webgpu).
Unexpected child process spawns from firefox.exe or thunderbird.exe shortly after rendering external content.
Outbound network connections from browser processes to previously unseen domains following navigation to untrusted pages.

Detection Strategies

Inventory installed Firefox and Thunderbird versions across endpoints and flag any build prior to 152.
Monitor crash telemetry for repeated faults in WebGPU code paths, which can indicate exploitation attempts.
Inspect web proxy and DNS logs for users visiting URLs that deliver WebGPU-heavy payloads from low-reputation domains.

Monitoring Recommendations

Enable EDR process-tree visibility for browser processes to catch post-exploitation behaviors such as shell spawns or LOLBin execution.
Correlate browser crash events with subsequent network egress and file-write activity in user profile directories.
Track Mozilla advisory feeds (MFSA-2026-57 and MFSA-2026-60) for related variants.

How to Mitigate CVE-2026-12293

Immediate Actions Required

Upgrade Firefox to version 152 or later on all managed endpoints.
Upgrade Thunderbird to version 152 or later, including server-deployed mail clients.
Restart browser and mail client processes after patching to ensure the vulnerable code is unloaded.

Patch Information

Mozilla released fixes in Firefox 152 and Thunderbird 152. Patch details are documented in Mozilla Security Advisory MFSA-2026-57 and Mozilla Security Advisory MFSA-2026-60. Administrators should deploy these updates through enterprise update channels or Mozilla's built-in updater.

Workarounds

Disable WebGPU by setting dom.webgpu.enabled to false in about:config until patches are deployed.
Block remote content rendering in Thunderbird by disabling automatic loading of HTML and remote resources in email.
Restrict access to untrusted websites through web filtering policies for users who cannot be patched immediately.

bash

# Configuration example: disable WebGPU via Firefox enterprise policy (policies.json)
{
  "policies": {
    "Preferences": {
      "dom.webgpu.enabled": {
        "Value": false,
        "Status": "locked"
      }
    }
  }
}