CVE-2026-2769: Mozilla Firefox Use-After-Free Vulnerability

CVE-2026-2769 Overview

CVE-2026-2769 is a use-after-free vulnerability in the Storage: IndexedDB component affecting Mozilla Firefox and Thunderbird. This memory corruption flaw occurs when the browser attempts to access memory that has already been freed within the IndexedDB storage subsystem. Attackers can potentially exploit this vulnerability through specially crafted web content to execute arbitrary code in the context of the browser process.

Critical Impact

Successful exploitation of this use-after-free vulnerability could allow remote attackers to execute arbitrary code, potentially leading to complete system compromise, data theft, or installation of malware. User interaction is required as the victim must visit a malicious website or open a crafted email in Thunderbird.

Affected Products

• Mozilla Firefox versions prior to 148
• Mozilla Firefox ESR versions prior to 115.33 and 140.8
• Mozilla Thunderbird versions prior to 148 and 140.8

Discovery Timeline

• 2026-02-24 - CVE-2026-2769 published to NVD
• 2026-02-25 - Last updated in NVD database

Technical Details for CVE-2026-2769

Vulnerability Analysis

This vulnerability is classified as CWE-416 (Use After Free), a memory corruption issue where the application continues to reference memory after it has been deallocated. In the context of the IndexedDB storage component, the browser's JavaScript engine may access freed memory when processing certain database operations, leading to undefined behavior.

The IndexedDB API provides a way for web applications to store significant amounts of structured data client-side. The use-after-free condition occurs during specific database transaction handling, where object references are not properly managed after memory deallocation. This creates a window of opportunity where an attacker can manipulate the freed memory region to redirect program execution or corrupt critical data structures.

Root Cause

The root cause lies in improper lifetime management of objects within the IndexedDB storage implementation. When certain database operations are performed in a specific sequence, the code path leads to premature deallocation of an object while references to that object still exist. Subsequent access to this dangling reference results in the use-after-free condition, allowing potential memory corruption.

Attack Vector

This vulnerability can be exploited remotely over a network. An attacker would need to craft malicious web content that triggers the vulnerable code path in the IndexedDB component. The attack requires user interaction—the victim must navigate to a malicious website using Firefox or open a specially crafted email in Thunderbird.

The exploitation mechanism involves manipulating IndexedDB operations through JavaScript to create the conditions necessary to trigger the use-after-free. Once triggered, an attacker could potentially gain code execution by controlling the contents of the freed memory region before the dangling pointer is accessed.

For detailed technical information about the vulnerability mechanism, refer to the Mozilla Bug Report #2014550.

Detection Methods for CVE-2026-2769

Indicators of Compromise

• Unexpected browser crashes or memory corruption errors in Firefox or Thunderbird processes
• Unusual IndexedDB activity patterns or malformed database operations in browser logs
• Detection of exploit kit traffic targeting Mozilla products in network monitoring systems
• Suspicious JavaScript execution patterns involving rapid IndexedDB transaction manipulation

Detection Strategies

• Deploy endpoint detection solutions capable of identifying memory corruption exploitation attempts
• Monitor for anomalous process behavior including unexpected child process spawning from Firefox or Thunderbird
• Implement browser-level security policies that restrict access to potentially dangerous APIs from untrusted sources
• Utilize network intrusion detection systems with signatures for known exploit kit delivery mechanisms

Monitoring Recommendations

• Enable browser crash reporting to capture forensic data from exploitation attempts
• Monitor system logs for signs of post-exploitation activity following browser process anomalies
• Configure SIEM rules to correlate browser crashes with suspicious network activity
• Track Firefox and Thunderbird version deployment across the organization to identify vulnerable installations

How to Mitigate CVE-2026-2769

Immediate Actions Required

• Update Mozilla Firefox to version 148 or later immediately
• Update Mozilla Firefox ESR to version 115.33 or 140.8 depending on your ESR track
• Update Mozilla Thunderbird to version 148 or 140.8 depending on your release channel
• Prioritize patching systems exposed to untrusted web content or email

Patch Information

Mozilla has released security updates addressing this vulnerability across multiple product lines. Organizations should apply the appropriate patches based on their deployment:

• Firefox: Update to version 148 or later - Mozilla Security Advisory MFSA-2026-13
• Firefox ESR: Update to version 115.33 or 140.8 - Mozilla Security Advisory MFSA-2026-14 and MFSA-2026-15
• Thunderbird: Update to version 148 or 140.8 - Mozilla Security Advisory MFSA-2026-16 and MFSA-2026-17

Workarounds

• Consider temporarily using an alternative browser if immediate patching is not possible
• Implement network-level filtering to block known malicious sites targeting this vulnerability
• Enable enhanced tracking protection and strict security settings in Firefox
• Restrict JavaScript execution on untrusted websites using browser extensions like NoScript until patches can be applied

# Example: Force Firefox update check via command line
firefox --check-update

# Verify installed Firefox version
firefox --version

# For enterprise deployments, use policy configuration
# Create or update policies.json in distribution folder
cat /usr/lib/firefox/distribution/policies.json