CVE-2025-14326: Mozilla Firefox Use-After-Free Vulnerability

CVE-2025-14326 Overview

CVE-2025-14326 is a use-after-free vulnerability [CWE-416] in the Audio/Video: Gecko Media Plugin (GMP) component of Mozilla Firefox and Mozilla Thunderbird. The flaw allows remote attackers to trigger memory corruption by serving crafted media content, potentially leading to arbitrary code execution within the browser process. Mozilla addressed the vulnerability in Firefox 146 and Thunderbird 146. The issue affects confidentiality, integrity, and availability, and requires no authentication or user interaction beyond visiting an attacker-controlled page.

Critical Impact
Remote attackers can exploit the use-after-free condition in the GMP component to corrupt memory and execute arbitrary code without authentication.

Affected Products

Mozilla Firefox versions prior to 146
Mozilla Thunderbird versions prior to 146
Audio/Video: GMP (Gecko Media Plugin) component

Discovery Timeline

2025-12-09 - CVE-2025-14326 published to the National Vulnerability Database (NVD)
2026-04-13 - Last updated in NVD database

Technical Details for CVE-2025-14326

Vulnerability Analysis

The vulnerability resides in the Gecko Media Plugin (GMP) subsystem, which Firefox and Thunderbird use to decode protected audio and video content. A use-after-free condition occurs when the component continues to reference memory that has already been freed during media processing. An attacker controlling the freed memory region can influence program flow when the dangling pointer is dereferenced.

The vulnerability is reachable over the network through standard media delivery channels. An attacker hosts crafted media on a website and lures the victim to load the page, or embeds the payload in HTML email rendered by Thunderbird. Successful exploitation grants code execution in the context of the content process.

Root Cause

The root cause is improper object lifetime management within the Audio/Video GMP component. An object referenced by an active pointer is released without invalidating that pointer, leaving a stale reference. Subsequent operations on the freed object create an attacker-controllable state that can be leveraged for memory corruption and control-flow hijacking.

Attack Vector

Exploitation occurs over the network without authentication. An attacker delivers malicious media content through a web page, advertisement, iframe, or HTML email body. When the GMP component processes the content, the use-after-free is triggered. No user interaction beyond loading the resource is required.

No public proof-of-concept code or technical exploit details have been released. Refer to the Mozilla Bug Report #1840666 and the Mozilla Security Advisory MFSA-2025-92 for vendor analysis.

Detection Methods for CVE-2025-14326

Indicators of Compromise

Firefox or Thunderbird content processes crashing while rendering media on untrusted pages
Unexpected child process spawns originating from firefox.exe, firefox-bin, or thunderbird binaries
Outbound network connections to unfamiliar destinations immediately following media playback
Browser telemetry showing repeated GMP plugin crashes (plugin-container faults)

Detection Strategies

Inventory installed Firefox and Thunderbird versions across endpoints and flag any builds prior to 146
Monitor endpoint detection and response (EDR) telemetry for anomalous code execution paths originating from browser content processes
Correlate browser crash reports with web proxy logs to identify domains delivering malformed media
Apply behavioral detections for memory corruption exploitation patterns such as ROP chains or unusual JIT memory allocations

Monitoring Recommendations

Enable centralized collection of browser crash dumps and forward them to a security data lake for analysis
Track DNS and HTTP/HTTPS requests for .mp4, .webm, and DRM-protected streams from low-reputation domains
Alert on Firefox or Thunderbird processes loading unsigned modules or invoking shell interpreters
Audit Thunderbird message rendering events that coincide with content process restarts

How to Mitigate CVE-2025-14326

Immediate Actions Required

Upgrade Firefox to version 146 or later and Thunderbird to version 146 or later on all endpoints
Prioritize patching for systems used for browsing untrusted content or processing external email
Restart Firefox and Thunderbird after installation so the patched binaries are loaded into memory
Validate patch deployment through software inventory checks and version reporting

Patch Information

Mozilla released fixes in Firefox 146 and Thunderbird 146. Refer to Mozilla Security Advisory MFSA-2025-92 and Mozilla Security Advisory MFSA-2025-95 for the complete list of patched issues and download links.

Workarounds

Disable autoplay and DRM-protected media playback in about:preferences until patches are deployed
Restrict Thunderbird to display messages in plain text mode to limit media rendering
Apply web filtering policies that block untrusted streaming and advertising domains
Run browsers under least-privilege user accounts and enforce application sandboxing

bash

# Verify installed Firefox version on Linux endpoints
firefox --version

# Verify installed Thunderbird version
thunderbird --version

# Example: enforce minimum version through configuration management
# Fail compliance if version is below 146