CVE-2026-4697: Mozilla Firefox Buffer Overflow Vulnerability

CVE-2026-4697 Overview

CVE-2026-4697 is a boundary condition error vulnerability affecting Mozilla Firefox, Firefox ESR, and Thunderbird. The flaw exists in the Audio/Video: Web Codecs component, where incorrect boundary conditions can lead to improper handling of exceptional conditions (CWE-754). This vulnerability can be exploited remotely over a network without requiring user authentication or interaction.

Critical Impact

Attackers can exploit this boundary condition vulnerability remotely to cause denial of service conditions affecting availability of affected Mozilla products.

Affected Products

• Mozilla Firefox < 149
• Mozilla Firefox ESR < 140.9
• Mozilla Thunderbird < 149
• Mozilla Thunderbird < 140.9

Discovery Timeline

• 2026-03-24 - CVE-2026-4697 published to NVD
• 2026-03-26 - Last updated in NVD database

Technical Details for CVE-2026-4697

Vulnerability Analysis

This vulnerability stems from improper handling of exceptional conditions (CWE-754) within the Web Codecs component responsible for audio and video processing in Mozilla products. The boundary condition error allows attackers to trigger unexpected behavior when the component processes malformed or specially crafted media data. The flaw is exploitable remotely without authentication, and successful exploitation can result in complete loss of system availability. However, the vulnerability does not impact data confidentiality or integrity based on the vulnerability characteristics.

Root Cause

The root cause is incorrect boundary condition validation in the Audio/Video: Web Codecs component. When processing media content, the component fails to properly validate input boundaries before processing, leading to improper handling of exceptional conditions. This type of vulnerability (CWE-754) occurs when software does not check for unusual or exceptional conditions that may disrupt normal program flow.

Attack Vector

The vulnerability can be exploited remotely over a network. An attacker could craft malicious media content that triggers the boundary condition error when processed by the Web Codecs component. Since the attack requires no privileges and no user interaction, a victim simply needs to visit a malicious webpage or open content containing the specially crafted media payload. The attack complexity is low, making this vulnerability accessible to a wide range of threat actors.

The vulnerability manifests when the Web Codecs component processes audio or video data without proper boundary validation. Technical details can be found in Mozilla Bug Report #2020422 and the associated security advisories.

Detection Methods for CVE-2026-4697

Indicators of Compromise

• Unexpected browser crashes or freezes when processing media content
• Abnormal memory consumption patterns in Firefox or Thunderbird processes
• Browser process termination without user initiation during media playback
• Error logs indicating Web Codecs component failures

Detection Strategies

• Monitor for repeated browser crashes associated with media processing operations
• Implement network-based detection for malformed media content targeting the Web Codecs component
• Deploy endpoint detection to identify unusual browser process behavior during media rendering
• Review browser crash reports for patterns indicating exploitation attempts

Monitoring Recommendations

• Enable crash reporting in Firefox and Thunderbird to capture exploitation attempts
• Monitor network traffic for suspicious media content delivery to organizational endpoints
• Implement browser telemetry analysis to detect anomalous Web Codecs behavior
• Review security logs for patterns consistent with denial of service attacks targeting browsers

How to Mitigate CVE-2026-4697

Immediate Actions Required

• Update Mozilla Firefox to version 149 or later immediately
• Update Mozilla Firefox ESR to version 140.9 or later
• Update Mozilla Thunderbird to version 149 or later
• Verify all instances of affected Mozilla products across your environment are patched

Patch Information

Mozilla has released security patches addressing this vulnerability. Users should update to the following fixed versions:

• Firefox: Version 149 or later
• Firefox ESR: Version 140.9 or later
• Thunderbird: Version 149 or later

For detailed patch information, refer to Mozilla Security Advisory MFSA-2026-20, Mozilla Security Advisory MFSA-2026-22, Mozilla Security Advisory MFSA-2026-23, and Mozilla Security Advisory MFSA-2026-24.

Workarounds

• Consider temporarily disabling Web Codecs functionality if updates cannot be immediately applied
• Implement network-level filtering to block potentially malicious media content
• Restrict browser usage to trusted sites until patches can be deployed
• Use browser isolation technologies to contain potential exploitation attempts

# Check current Firefox version on Linux
firefox --version

# Update Firefox on Debian/Ubuntu systems
sudo apt update && sudo apt upgrade firefox

# Update Firefox on Red Hat/Fedora systems
sudo dnf update firefox