CVE-2025-9182: Mozilla Firefox DOS Vulnerability

CVE-2025-9182 Overview

CVE-2025-9182 is a denial-of-service vulnerability in the Graphics: WebRender component used by Mozilla Firefox and Mozilla Thunderbird. The flaw allows a remote attacker to trigger excessive memory allocation, leading to an out-of-memory (OOM) condition that crashes the browser process. The issue is tracked under [CWE-400] Uncontrolled Resource Consumption and requires no authentication or user interaction beyond visiting a malicious page. Mozilla addressed the vulnerability in Firefox 142, Firefox ESR 140.2, Thunderbird 142, and Thunderbird 140.2.

Critical Impact
A remote attacker can serve crafted web content that exhausts available memory in the WebRender graphics pipeline, terminating the browser or mail client process and disrupting user availability.

Affected Products

Mozilla Firefox versions prior to 142
Mozilla Firefox ESR versions prior to 140.2
Mozilla Thunderbird versions prior to 142 and prior to 140.2

Discovery Timeline

2025-08-19 - CVE-2025-9182 published to NVD
2026-04-13 - Last updated in NVD database

Technical Details for CVE-2025-9182

Vulnerability Analysis

The vulnerability resides in WebRender, the GPU-accelerated rendering engine that Firefox and Thunderbird use to composite web content. WebRender translates Document Object Model (DOM) structures into draw calls executed on the GPU. When the component processes specially crafted graphics input, it fails to bound an internal allocation, requesting more memory than the host can satisfy. The resulting out-of-memory condition aborts the content or rendering process, producing a denial-of-service outcome. The impact is limited to availability, with no confidentiality or integrity consequences according to the published CVSS vector.

Root Cause

The root cause is uncontrolled resource consumption [CWE-400] in the WebRender code path. The component accepts attacker-influenced size or count parameters from rendered content without enforcing a sufficient upper bound. WebRender then attempts the corresponding allocation, exhausting heap memory. Mozilla classifies the defect as a memory-safety / resource-handling issue and has corrected it in the listed releases.

Attack Vector

The attack is network-reachable and requires no privileges. An attacker hosts a page or embeds content that exercises the vulnerable WebRender code path. When a victim loads the page in a vulnerable Firefox build, or renders HTML email content in a vulnerable Thunderbird build, the rendering process attempts an oversized allocation and is terminated. Refer to the Mozilla Bug Report #1975837 and the Mozilla Security Advisory MFSA-2025-64 for technical context.

// No verified proof-of-concept code is available for this CVE.
// The vulnerability is triggered by crafted graphics content processed
// by the WebRender rendering pipeline, leading to out-of-memory abort.

Detection Methods for CVE-2025-9182

Indicators of Compromise

Repeated unexpected crashes of firefox.exe, firefox-bin, or thunderbird.exe processes with out-of-memory exit codes.
Crash reporter submissions referencing the WebRender component or gfx::wr modules.
Spikes in private working-set memory for browser content processes immediately before termination.

Detection Strategies

Inventory installed Firefox and Thunderbird builds and flag versions below Firefox 142, Firefox ESR 140.2, Thunderbird 142, or Thunderbird 140.2.
Monitor endpoint telemetry for abnormal browser process exits correlated with web traffic to untrusted domains.
Correlate proxy or DNS logs with browser crash events to identify content-driven denial-of-service attempts.

Monitoring Recommendations

Enable browser crash reporting and forward reports to a centralized analysis pipeline.
Track memory consumption thresholds for browser and mail client processes and alert on sudden growth followed by termination.
Review Mozilla advisories MFSA-2025-64, MFSA-2025-67, MFSA-2025-70, and MFSA-2025-72 for related fixes shipped in the same release cycle.

How to Mitigate CVE-2025-9182

Immediate Actions Required

Upgrade Firefox to version 142 or later on all managed endpoints.
Upgrade Firefox ESR deployments to version 140.2 or later.
Upgrade Thunderbird to version 142 or to 140.2 on the ESR-equivalent channel.
Verify update channels are functional and restart browser and mail client processes to apply the new builds.

Patch Information

Mozilla fixed CVE-2025-9182 in Firefox 142, Firefox ESR 140.2, Thunderbird 142, and Thunderbird 140.2. Patch details are available in the Mozilla Security Advisory MFSA-2025-64, MFSA-2025-67, MFSA-2025-70, and MFSA-2025-72. Administrators should validate that managed installations report the patched build numbers after deployment.

Workarounds

Restrict browsing of untrusted web content on hosts that cannot be immediately patched.
Disable WebRender via about:config by setting gfx.webrender.all to false as a temporary measure where supported, accepting potential rendering performance impact.
Display Thunderbird messages in plain text mode to limit rendering of remote HTML content until updates are applied.

bash

# Example: enforce minimum Firefox version via enterprise policy (Linux)
cat <<'EOF' > /etc/firefox/policies/policies.json
{
  "policies": {
    "DisableAppUpdate": false,
    "AppAutoUpdate": true,
    "OverrideFirstRunPage": "",
    "Preferences": {
      "gfx.webrender.all": {
        "Value": false,
        "Status": "locked"
      }
    }
  }
}
EOF