CVE-2025-13020: Mozilla Firefox Use-After-Free Vulnerability

CVE-2025-13020 Overview

CVE-2025-13020 is a use-after-free vulnerability in the WebRTC Audio/Video component of Mozilla Firefox, Firefox ESR, and Thunderbird. This memory corruption flaw occurs when the browser improperly handles memory associated with WebRTC audio and video processing, potentially allowing an attacker to execute arbitrary code within the context of the user's browser session.

Critical Impact

This use-after-free vulnerability in WebRTC could allow remote attackers to achieve code execution through specially crafted web content, potentially leading to complete compromise of user confidentiality, integrity, and system availability.

Affected Products

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

Discovery Timeline

• 2025-11-11 - CVE-2025-13020 published to NVD
• 2026-04-13 - Last updated in NVD database

Technical Details for CVE-2025-13020

Vulnerability Analysis

This vulnerability is classified as CWE-416 (Use After Free), a memory corruption issue that occurs when a program continues to reference memory after it has been freed. In the context of Mozilla's WebRTC implementation, the Audio/Video component contains a flaw where freed memory associated with media stream processing can be accessed again, leading to undefined behavior.

The vulnerability requires user interaction to exploit—specifically, a user must visit a malicious webpage or be exposed to crafted WebRTC content. Once triggered, an attacker could potentially hijack program execution flow, leading to arbitrary code execution with the privileges of the browser process. This could result in complete compromise of confidentiality, integrity, and availability of the affected system.

Root Cause

The root cause of CVE-2025-13020 lies in improper memory lifecycle management within the WebRTC Audio/Video component. When certain audio or video stream objects are deallocated, references to these objects may persist in other parts of the codebase. Subsequent operations that attempt to access these dangling pointers result in use-after-free conditions.

This type of vulnerability typically arises from complex object lifetimes in multimedia processing code, where asynchronous operations and callback mechanisms can lead to scenarios where memory is freed while still being referenced elsewhere.

Attack Vector

The attack vector for this vulnerability is network-based, requiring no privileges but necessitating user interaction. An attacker could exploit this vulnerability by:

1. Crafting a malicious webpage containing WebRTC content designed to trigger the use-after-free condition
2. Luring a victim to visit the webpage through phishing or social engineering
3. The malicious WebRTC content triggers improper memory handling in the Audio/Video component
4. Memory corruption occurs, potentially allowing the attacker to execute arbitrary code

The vulnerability mechanism involves timing-sensitive operations in WebRTC stream handling. Technical details are available in Mozilla Bug Report #1995686 and the associated security advisories.

Detection Methods for CVE-2025-13020

Indicators of Compromise

• Unexpected browser crashes or instability when visiting websites with WebRTC functionality
• Anomalous memory access patterns in Firefox or Thunderbird processes
• Suspicious network connections initiated from browser processes following WebRTC sessions
• Unexpected child process spawning from browser application contexts

Detection Strategies

• Monitor for exploitation attempts by deploying endpoint detection solutions capable of identifying memory corruption exploitation techniques
• Implement browser-level telemetry to detect anomalous WebRTC behavior patterns
• Deploy network monitoring to identify connections to known malicious domains serving exploit content
• Use SentinelOne Singularity to detect post-exploitation behaviors such as unauthorized code execution from browser processes

Monitoring Recommendations

• Enable crash reporting in Mozilla products to identify potential exploitation attempts
• Monitor system logs for browser process anomalies, including unexpected memory access violations
• Implement web content filtering to block access to known malicious sites
• Track browser version deployments across the organization to ensure vulnerable versions are identified

How to Mitigate CVE-2025-13020

Immediate Actions Required

• Update Mozilla Firefox to version 145 or later immediately
• Update Mozilla Firefox ESR to version 140.5 or later
• Update Mozilla Thunderbird to version 145 or 140.5 or later
• Consider temporarily disabling WebRTC functionality in environments where updates cannot be immediately applied

Patch Information

Mozilla has released security patches addressing this vulnerability in the following versions:

• Firefox 145 - Mozilla Security Advisory MFSA-2025-87
• Firefox ESR 140.5 - Mozilla Security Advisory MFSA-2025-88
• Thunderbird 145 - Mozilla Security Advisory MFSA-2025-90
• Thunderbird 140.5 - Mozilla Security Advisory MFSA-2025-91

Organizations should prioritize deploying these updates through their software management infrastructure.

Workarounds

• Disable WebRTC in Firefox by setting media.peerconnection.enabled to false in about:config
• Use browser policies to restrict access to WebRTC functionality in enterprise environments
• Implement network-level controls to block WebRTC traffic if the feature is not required
• Deploy web content filtering to prevent access to potentially malicious sites until patching is complete

# Firefox policy configuration to disable WebRTC (policies.json)
# Place in Firefox installation directory under distribution/policies.json
{
  "policies": {
    "Preferences": {
      "media.peerconnection.enabled": {
        "Value": false,
        "Status": "locked"
      }
    }
  }
}