CVE-2025-13012: Mozilla Firefox Race Condition Vulnerability

CVE-2025-13012 Overview

CVE-2025-13012 is a race condition vulnerability in the Graphics component of Mozilla Firefox and Thunderbird. The flaw affects concurrent access to graphics-related resources, creating a window where attackers can manipulate timing-dependent operations. Mozilla addressed the issue in Firefox 145, Firefox ESR 140.5, Firefox ESR 115.30, Thunderbird 145, and Thunderbird 140.5.

The vulnerability is classified under CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization). Exploitation requires user interaction such as visiting a crafted web page, and the attack complexity is high due to the timing-sensitive nature of race conditions.

Critical Impact

Successful exploitation can compromise the confidentiality, integrity, and availability of the affected browser process, potentially enabling memory corruption or sandbox-related issues.

Affected Products

• Mozilla Firefox versions prior to 145
• Mozilla Firefox ESR versions prior to 140.5 and 115.30
• Mozilla Thunderbird versions prior to 145 and 140.5

Discovery Timeline

• 2025-11-11 - CVE-2025-13012 published to NVD
• 2026-04-13 - Last updated in NVD database

Technical Details for CVE-2025-13012

Vulnerability Analysis

The vulnerability resides in the Graphics component shared across Mozilla Firefox and Thunderbird. A race condition occurs when multiple threads access shared graphics resources without proper synchronization. An attacker who wins the race can manipulate the state of these resources between the time of check and the time of use.

The Graphics component handles rendering, compositing, and GPU-accelerated operations. These subsystems frequently spawn worker threads and perform asynchronous operations on shared buffers. Improper synchronization in this context can lead to memory safety issues, including use-after-free or out-of-bounds access on graphics objects.

Exploitation requires user interaction, meaning the victim must load attacker-controlled content. The high attack complexity reflects the difficulty of reliably winning the race under real-world conditions. However, successful exploitation can yield significant impact on the browser process.

Root Cause

The root cause is improper synchronization of concurrent operations within the Graphics component, falling under CWE-362. Shared graphics state is accessed by multiple execution contexts without sufficient locking or atomicity guarantees, creating an exploitable timing window.

Attack Vector

The attack vector is network-based. An attacker hosts a malicious web page or HTML email that triggers concurrent graphics operations. When the victim loads the content in a vulnerable version of Firefox or Thunderbird, the race condition can be triggered. See the Mozilla Bug Report #1991458 and Mozilla Security Advisory MFSA-2025-87 for additional context.

No public proof-of-concept exploit code is available for this vulnerability at the time of publication.

Detection Methods for CVE-2025-13012

Indicators of Compromise

• Unexpected Firefox or Thunderbird process crashes with stack traces referencing graphics modules such as gfx, webrender, or layers.
• Browser child process terminations correlated with visits to untrusted web content.
• Anomalous memory usage spikes or repeated renderer restarts on endpoints running outdated Mozilla versions.

Detection Strategies

• Inventory installed Firefox and Thunderbird versions across the environment and flag any builds preceding 145, ESR 140.5, ESR 115.30, or Thunderbird 140.5.
• Monitor crash telemetry and Windows Error Reporting events for repeated browser faults that may indicate exploitation attempts.
• Correlate web proxy logs with browser process anomalies to identify users visiting suspicious URLs prior to crashes.

Monitoring Recommendations

• Enable centralized collection of browser crash reports and forward them to a SIEM for correlation.
• Alert on outdated Mozilla installations detected by endpoint inventory or vulnerability management tools.
• Track outbound connections from browser processes to newly observed or low-reputation domains.

How to Mitigate CVE-2025-13012

Immediate Actions Required

• Update Firefox to version 145 or later on all endpoints.
• Update Firefox ESR to 140.5 or 115.30, depending on the deployed branch.
• Update Thunderbird to version 145 or 140.5.
• Restart affected applications after patching to ensure updated binaries are loaded.

Patch Information

Mozilla released patches addressing CVE-2025-13012 across multiple advisories. Refer to Mozilla Security Advisory MFSA-2025-87, MFSA-2025-88, MFSA-2025-89, MFSA-2025-90, and MFSA-2025-91 for vendor guidance and release notes.

Workarounds

• Restrict browsing to trusted sites until patches are deployed across the fleet.
• Disable hardware acceleration in Firefox and Thunderbird preferences to reduce graphics subsystem concurrency, accepting performance trade-offs.
• Use enterprise policies to enforce automatic updates for Mozilla products.

# Verify Firefox version on Linux/macOS
firefox --version

# Verify Thunderbird version
thunderbird --version

# Example: enforce automatic updates via Firefox policies.json
# Place in the distribution directory of the Firefox install
cat <<EOF > /etc/firefox/policies/policies.json
{
  "policies": {
    "DisableAppUpdate": false,
    "AppAutoUpdate": true
  }
}
EOF