CVE-2026-4704: Mozilla Firefox DoS Vulnerability

CVE-2026-4704 Overview

CVE-2026-4704 is a denial-of-service vulnerability in the WebRTC: Signaling component affecting Mozilla Firefox and Thunderbird. The vulnerability allows remote attackers to cause application crashes or unresponsive states by exploiting flaws in the WebRTC signaling implementation, disrupting normal browser operations without requiring user interaction.

Critical Impact

Remote attackers can trigger denial-of-service conditions in affected Firefox and Thunderbird installations through malicious WebRTC signaling, causing browser crashes and service disruption for end users.

Affected Products

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

Discovery Timeline

• 2026-03-24 - CVE CVE-2026-4704 published to NVD
• 2026-03-25 - Last updated in NVD database

Technical Details for CVE-2026-4704

Vulnerability Analysis

This denial-of-service vulnerability resides in the WebRTC Signaling component of Mozilla's browser and email client applications. WebRTC (Web Real-Time Communication) is a critical technology enabling peer-to-peer communication for features like video conferencing, voice calls, and data sharing directly in the browser.

The vulnerability is classified under CWE-400 (Uncontrolled Resource Consumption), indicating that the flaw allows attackers to consume excessive system resources, leading to service degradation or complete application failure. The network-based attack vector means exploitation can occur remotely without requiring local access to the target system.

Root Cause

The root cause stems from improper resource management within the WebRTC signaling implementation. When processing malformed or specially crafted signaling messages, the affected components fail to properly validate or limit resource consumption, allowing an attacker to exhaust available resources and trigger a denial-of-service condition. This type of vulnerability typically occurs when input validation is insufficient or when resource allocation lacks appropriate bounds checking.

Attack Vector

The attack can be executed remotely over the network without requiring authentication or user interaction. An attacker could potentially exploit this vulnerability by:

1. Crafting malicious WebRTC signaling messages designed to trigger resource exhaustion
2. Delivering these messages to a victim's browser through a malicious website or compromised web application
3. Causing the browser to enter an unresponsive state or crash entirely

The vulnerability affects the availability of the application without compromising confidentiality or integrity of data. For detailed technical information, refer to the Mozilla Bug Report #2014868 and the official security advisories.

Detection Methods for CVE-2026-4704

Indicators of Compromise

• Unexpected Firefox or Thunderbird crashes during WebRTC-enabled web sessions
• High memory or CPU consumption by browser processes when visiting specific websites
• Repeated browser hangs or freezes during video conferencing or real-time communication features
• Unusual network traffic patterns associated with WebRTC signaling protocols

Detection Strategies

• Monitor browser crash reports and error logs for patterns indicating WebRTC signaling failures
• Implement network monitoring to detect anomalous WebRTC signaling traffic that may indicate exploitation attempts
• Deploy endpoint detection and response (EDR) solutions to identify process-level abnormalities in Firefox and Thunderbird
• Utilize SentinelOne's behavioral AI to detect resource exhaustion patterns associated with DoS attacks

Monitoring Recommendations

• Enable enhanced logging for WebRTC components to capture signaling events and potential exploitation attempts
• Configure alerts for sudden spikes in browser process resource consumption
• Monitor for multiple browser restarts within short time periods that may indicate exploitation
• Review network traffic for known malicious patterns targeting WebRTC implementations

How to Mitigate CVE-2026-4704

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 140.9 or later
• Prioritize updates for systems where WebRTC functionality is actively used
• Review organizational browser deployment policies to ensure automatic updates are enabled

Patch Information

Mozilla has released security updates addressing this vulnerability. The fixes are documented in the following security advisories:

• Mozilla Security Advisory MFSA-2026-20
• Mozilla Security Advisory MFSA-2026-22
• Mozilla Security Advisory MFSA-2026-23
• Mozilla Security Advisory MFSA-2026-24

Organizations should obtain and deploy these updates through their standard software distribution mechanisms or directly from Mozilla's official channels.

Workarounds

• Consider disabling WebRTC functionality in Firefox through about:config by setting media.peerconnection.enabled to false until patches can be applied
• Implement network-level filtering to block suspicious WebRTC signaling traffic
• Deploy browser isolation technologies to contain potential exploitation attempts
• Restrict access to untrusted websites that may attempt to exploit WebRTC vulnerabilities

# Firefox WebRTC mitigation via user preferences
# Add to user.js or set via about:config
user_pref("media.peerconnection.enabled", false);
user_pref("media.peerconnection.ice.default_address_only", true);
user_pref("media.peerconnection.ice.no_host", true);