CVE-2026-6753: Mozilla Firefox Buffer Overflow Vulnerability

CVE-2026-6753 Overview

CVE-2026-6753 is a high-severity boundary condition vulnerability affecting Mozilla's WebRTC component in Firefox and Thunderbird. The flaw stems from incorrect boundary conditions (CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer) that could allow an attacker to perform out-of-bounds operations when processing WebRTC-related data. This vulnerability impacts confidentiality, integrity, and availability of affected systems.

Critical Impact

Network-accessible vulnerability in WebRTC component allows unauthenticated remote attackers to potentially compromise browser integrity and leak sensitive information without user interaction.

Affected Products

• Mozilla Firefox versions prior to 150
• Mozilla Firefox ESR versions prior to 140.10
• Mozilla Thunderbird versions prior to 150
• Mozilla Thunderbird ESR versions prior to 140.10

Discovery Timeline

• April 21, 2026 - CVE-2026-6753 published to NVD
• April 22, 2026 - Last updated in NVD database

Technical Details for CVE-2026-6753

Vulnerability Analysis

This vulnerability exists in the WebRTC (Web Real-Time Communication) component used by Mozilla Firefox and Thunderbird for real-time peer-to-peer communication features. The issue involves improper boundary condition validation when processing WebRTC data, which falls under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer).

WebRTC is a critical browser component that handles real-time audio, video, and data communications. The boundary condition error could allow operations to occur outside the intended memory buffer boundaries, potentially leading to information disclosure, memory corruption, or unexpected application behavior.

Root Cause

The root cause is improper validation of boundary conditions within the WebRTC component's data processing routines. When handling specific WebRTC operations, the component fails to properly verify that operations remain within expected memory buffer bounds, leading to potential out-of-bounds memory access.

Attack Vector

The vulnerability is exploitable over the network without requiring authentication or user interaction. An attacker could craft malicious WebRTC traffic or host a malicious website that triggers the vulnerable code path when a victim visits the page or engages in WebRTC communication. The attack does not require elevated privileges and can be executed remotely against any user running an affected version of Firefox or Thunderbird.

The vulnerability affects the confidentiality, integrity, and availability of the target system, though each individual impact is rated as low, resulting in the overall high severity classification.

Detection Methods for CVE-2026-6753

Indicators of Compromise

• Unusual memory access patterns in Firefox or Thunderbird processes related to WebRTC operations
• Unexpected browser crashes or hangs during WebRTC-enabled web sessions
• Abnormal network traffic patterns associated with WebRTC STUN/TURN communications
• Memory consumption anomalies in browser processes during video/audio conferencing

Detection Strategies

• Monitor for unexpected crashes in firefox.exe or thunderbird.exe processes, particularly during WebRTC usage
• Implement network monitoring for suspicious WebRTC traffic patterns or connections to unknown STUN/TURN servers
• Deploy endpoint detection rules to identify attempts to exploit boundary condition vulnerabilities in browser processes
• Review browser telemetry for WebRTC-related error conditions that may indicate exploitation attempts

Monitoring Recommendations

• Enable crash reporting in Firefox and Thunderbird to capture potential exploitation attempts
• Implement browser version auditing to identify systems running vulnerable versions
• Configure network security monitoring to detect anomalous WebRTC traffic patterns
• Monitor security advisory feeds from Mozilla for additional indicators or detection guidance

How to Mitigate CVE-2026-6753

Immediate Actions Required

• Update Mozilla Firefox to version 150 or later immediately
• Update Mozilla Firefox ESR to version 140.10 or later
• Update Mozilla Thunderbird to version 150 or later
• Update Mozilla Thunderbird ESR to version 140.10 or later
• Verify updates have been applied across all managed endpoints

Patch Information

Mozilla has released security updates addressing this vulnerability. The fix is included in Firefox 150, Firefox ESR 140.10, Thunderbird 150, and Thunderbird 140.10. Organizations should prioritize deployment of these updates.

For detailed patch information, refer to the official Mozilla Security Advisories:

• Mozilla Security Advisory MFSA-2026-30
• Mozilla Security Advisory MFSA-2026-32
• Mozilla Security Advisory MFSA-2026-33
• Mozilla Security Advisory MFSA-2026-34

Additional technical details can be found in the Mozilla Bug Report #2027501.

Workarounds

• Disable WebRTC functionality in Firefox by navigating to about:config and setting media.peerconnection.enabled to false
• Block access to untrusted websites that may leverage WebRTC features until patching is complete
• Consider using browser isolation technologies for high-risk browsing activities
• Implement network-level controls to restrict WebRTC traffic where operationally feasible

# Firefox WebRTC disable via user.js configuration
# Add to user.js in Firefox profile directory
user_pref("media.peerconnection.enabled", false);
user_pref("media.navigator.enabled", false);