CVE-2025-11719: Mozilla Firefox Use-After-Free Vulnerability

CVE-2025-11719 Overview

CVE-2025-11719 is a use-after-free memory corruption vulnerability affecting Mozilla Firefox and Thunderbird on Windows systems. Starting in Thunderbird 143, the use of the native messaging API by web extensions on Windows could lead to crashes caused by use-after-free memory corruption. This vulnerability allows remote attackers to potentially execute arbitrary code or cause denial of service conditions without requiring any privileges or user interaction.

Critical Impact

This use-after-free vulnerability in the native messaging API could allow attackers to achieve remote code execution or cause application crashes on affected Windows systems running Firefox or Thunderbird versions prior to 144.

Affected Products

• Mozilla Firefox < 144
• Mozilla Thunderbird < 144
• Microsoft Windows (as the affected platform)

Discovery Timeline

• October 14, 2025 - CVE-2025-11719 published to NVD
• November 14, 2025 - Last updated in NVD database

Technical Details for CVE-2025-11719

Vulnerability Analysis

This vulnerability is classified as CWE-416 (Use After Free), a memory corruption vulnerability that occurs when a program continues to use a pointer after the memory it references has been freed. In the context of CVE-2025-11719, the native messaging API used by web extensions on Windows fails to properly manage memory lifecycle, leading to a condition where freed memory is subsequently accessed.

Use-after-free vulnerabilities are particularly dangerous because they can lead to arbitrary code execution. When memory is freed and then reallocated for a different purpose, the dangling pointer may allow an attacker to manipulate the contents of the reallocated memory, potentially gaining control over program execution flow.

Root Cause

The root cause of this vulnerability lies in improper memory management within the native messaging API implementation for web extensions on Windows platforms. When a web extension communicates with a native application through the native messaging API, the browser creates and manages memory structures to facilitate this communication. The vulnerability arises when these memory structures are freed prematurely while still being referenced by other parts of the code.

The issue was introduced in Thunderbird 143, suggesting a regression or new code path that failed to properly synchronize memory deallocation with the lifecycle of objects using that memory. This type of bug often occurs in complex multi-threaded environments where race conditions can lead to objects being freed while still in use.

Attack Vector

This vulnerability can be exploited remotely over the network without requiring authentication or user interaction. An attacker could craft a malicious web extension or leverage an existing extension to trigger the vulnerable code path in the native messaging API. The attack exploits the following characteristics:

• Network-accessible: The vulnerability can be triggered through normal browser/email client operations
• No privileges required: Attackers do not need any authenticated access to the system
• No user interaction: Exploitation can occur without explicit user action beyond having a vulnerable browser/client running

The native messaging API allows web extensions to exchange messages with native applications installed on the user's computer. By manipulating the message flow or timing of API calls, an attacker could trigger the use-after-free condition, potentially leading to code execution within the context of the browser or email client process.

For technical details on the specific bug, see the Mozilla Bug Report #1991950.

Detection Methods for CVE-2025-11719

Indicators of Compromise

• Unexpected crashes of Firefox or Thunderbird processes on Windows systems, particularly when web extensions are active
• Memory access violations or segmentation faults in browser/email client logs
• Suspicious web extension behavior involving native messaging API calls
• Unusual process behavior or child processes spawned from Firefox or Thunderbird

Detection Strategies

• Monitor for abnormal termination of Firefox (firefox.exe) or Thunderbird (thunderbird.exe) processes with memory-related error codes
• Implement application crash monitoring to detect repeated crashes that may indicate exploitation attempts
• Review installed web extensions for suspicious or unknown extensions that utilize native messaging capabilities
• Deploy endpoint detection rules to identify use-after-free exploitation patterns in browser processes

Monitoring Recommendations

• Enable crash reporting and aggregate crash data to identify patterns that may indicate exploitation
• Monitor network traffic for unusual activity from browser processes following extension-related operations
• Implement SentinelOne's behavioral AI to detect memory corruption exploitation attempts in real-time
• Review Windows Event Logs for application crashes with exception codes related to memory access violations (0xC0000005)

How to Mitigate CVE-2025-11719

Immediate Actions Required

• Update Mozilla Firefox to version 144 or later immediately
• Update Mozilla Thunderbird to version 144 or later immediately
• Audit installed web extensions and remove any unnecessary or suspicious extensions
• Consider temporarily disabling web extensions that utilize native messaging functionality until updates are applied

Patch Information

Mozilla has released security patches addressing this vulnerability in Firefox 144 and Thunderbird 144. Organizations should prioritize updating affected systems to these versions or later. Detailed patch information is available in the official Mozilla Security Advisories:

• Mozilla Security Advisory MFSA-2025-81 - Firefox security update
• Mozilla Security Advisory MFSA-2025-84 - Thunderbird security update

Workarounds

• Disable or remove web extensions that use native messaging capabilities until patches are applied
• Use browser profiles without extensions for sensitive activities
• Implement network segmentation to limit potential lateral movement if exploitation occurs
• Consider using alternative browsers on critical systems until patching is complete

# Verify Firefox version on Windows (PowerShell)
& "C:\Program Files\Mozilla Firefox\firefox.exe" --version | Select-String -Pattern "Mozilla Firefox"

# Verify Thunderbird version on Windows (PowerShell)
& "C:\Program Files\Mozilla Thunderbird\thunderbird.exe" --version | Select-String -Pattern "Thunderbird"

# List installed extensions directory for review
Get-ChildItem "$env:APPDATA\Mozilla\Firefox\Profiles\*\extensions" -Recurse -ErrorAction SilentlyContinue