CVE-2026-2757: Mozilla Firefox WebRTC Boundary Error

CVE-2026-2757 Overview

CVE-2026-2757 is a critical boundary condition vulnerability affecting the WebRTC Audio/Video component in Mozilla Firefox and Thunderbird. This flaw stems from incorrect boundary conditions that could allow an attacker to execute arbitrary code or cause memory corruption through specially crafted WebRTC media streams. The vulnerability is particularly dangerous because WebRTC functionality is commonly used for real-time communication features including video conferencing, audio calls, and peer-to-peer data sharing.

Critical Impact

This vulnerability allows remote attackers to potentially achieve code execution through malicious WebRTC content without requiring any user interaction or authentication, affecting both browser and email client users.

Affected Products

• Mozilla Firefox < 148
• Mozilla Firefox ESR < 115.33
• Mozilla Firefox ESR < 140.8
• Mozilla Thunderbird < 148
• Mozilla Thunderbird < 140.8

Discovery Timeline

• 2026-02-24 - CVE-2026-2757 published to NVD
• 2026-02-26 - Last updated in NVD database

Technical Details for CVE-2026-2757

Vulnerability Analysis

The vulnerability resides in the WebRTC Audio/Video component's handling of media stream data. WebRTC (Web Real-Time Communication) is a critical technology that enables real-time audio and video communication directly in web browsers and applications. The incorrect boundary conditions in this component can lead to memory corruption scenarios when processing malformed or adversarial media streams.

Boundary condition errors occur when software fails to properly validate the limits of data structures, arrays, or buffers before performing operations on them. In the context of the WebRTC Audio/Video component, this could manifest during the parsing or processing of audio/video frames, codec data, or RTP (Real-time Transport Protocol) packets.

The vulnerability can be triggered remotely through network-based attack vectors. An attacker could exploit this flaw by luring a victim to a malicious website that initiates a WebRTC session, or by sending crafted content through a compromised WebRTC peer connection. Since no user interaction beyond visiting a page or opening an email with embedded content is required, the exploitation barrier is relatively low.

Root Cause

The root cause is classified under CWE-1384, relating to improper handling of physical or environmental conditions that can affect boundary checks. The WebRTC Audio/Video component fails to properly validate boundary conditions when processing incoming media data. This allows attackers to craft input that exceeds expected boundaries, potentially leading to out-of-bounds memory access, buffer overflows, or other memory corruption issues.

Attack Vector

The attack vector is network-based, requiring no authentication or user privileges. An attacker can exploit this vulnerability by:

1. Hosting a malicious website that establishes a WebRTC connection with specially crafted media streams
2. Sending malicious content through email clients (Thunderbird) that process WebRTC-enabled content
3. Compromising a legitimate WebRTC peer to inject malicious media data during an active session

The vulnerability mechanism involves crafting WebRTC Audio/Video data that violates expected boundary conditions. When the vulnerable Firefox or Thunderbird versions process this malformed data, the incorrect boundary validation allows memory operations to occur outside intended buffer limits. Technical details of the specific boundary condition error can be found in Mozilla Bug Report #2001637.

Detection Methods for CVE-2026-2757

Indicators of Compromise

• Abnormal WebRTC session initiations from untrusted or suspicious domains
• Unusual memory consumption or crashes in Firefox or Thunderbird processes during WebRTC activity
• Network traffic containing malformed RTP packets or unexpected WebRTC signaling patterns
• Unexpected child process spawning from browser or email client applications

Detection Strategies

• Deploy network monitoring to identify suspicious WebRTC connection attempts to known malicious infrastructure
• Implement endpoint detection rules to monitor Firefox and Thunderbird processes for anomalous behavior including unexpected memory access patterns
• Configure browser crash reporting analysis to identify patterns consistent with boundary condition exploitation
• Utilize SentinelOne's behavioral AI to detect exploitation attempts through real-time process monitoring

Monitoring Recommendations

• Enable enhanced logging for WebRTC activity in enterprise environments
• Monitor for unexpected WebRTC-related network connections from Thunderbird, which may indicate email-based exploitation attempts
• Implement network segmentation to restrict WebRTC traffic to trusted domains where possible
• Review endpoint telemetry for Firefox and Thunderbird crash events that may indicate exploitation attempts

How to Mitigate CVE-2026-2757

Immediate Actions Required

• Update Mozilla Firefox to version 148 or later immediately
• Update Mozilla Firefox ESR to version 115.33 or 140.8 or later depending on your ESR track
• Update Mozilla Thunderbird to version 148 or 140.8 or later depending on your release channel
• Audit all systems for vulnerable versions using software inventory tools

Patch Information

Mozilla has released security patches addressing this vulnerability across multiple product lines. Organizations should prioritize updating to the following minimum versions:

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

• MFSA-2026-13
• MFSA-2026-14
• MFSA-2026-15
• MFSA-2026-16
• MFSA-2026-17

Workarounds

• Disable WebRTC functionality in Firefox by navigating to about:config and setting media.peerconnection.enabled to false
• Implement content security policies to restrict WebRTC usage to trusted domains
• Consider using browser isolation solutions for high-risk browsing activities
• Block access to untrusted websites that may attempt WebRTC connections

# Firefox WebRTC disable via user preferences
# Add to user.js or configure via enterprise policies
user_pref("media.peerconnection.enabled", false);
user_pref("media.navigator.enabled", false);