CVE-2026-4704 in Firefox
Summary
by MITRE • 03/24/2026
Denial-of-service in the WebRTC: Signaling component. This vulnerability affects Firefox < 149, Firefox ESR < 140.9, Thunderbird < 149, and Thunderbird < 140.9.
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Analysis
by VulDB Data Team • 04/16/2026
The vulnerability identified as CVE-2026-4704 represents a critical denial-of-service flaw within the WebRTC signaling component of Mozilla's browser applications. This weakness specifically targets the communication protocols used during the establishment of WebRTC connections, where browsers negotiate session parameters and exchange connection metadata. The issue manifests when the signaling process encounters malformed or specially crafted input that causes the application to crash or become unresponsive during the connection setup phase. Given that WebRTC is extensively used for real-time communication in web applications, this vulnerability presents a significant risk to user experience and system stability.
The technical root cause of this vulnerability lies in insufficient input validation within the WebRTC signaling handler routines. When processing incoming signaling messages, the affected Mozilla applications fail to properly sanitize or validate the structure and content of these communications, creating opportunities for malicious actors to craft payloads that trigger memory corruption or resource exhaustion conditions. The flaw operates at the application layer of the network stack, specifically targeting the session description protocol handling that occurs during WebRTC session initiation. This type of vulnerability maps directly to CWE-129, which describes improper validation of input boundaries, and CWE-476, which addresses null pointer dereference conditions that can occur during improper input handling.
The operational impact of this vulnerability extends beyond simple service disruption, as it can be exploited to create persistent denial-of-service conditions that affect user sessions and potentially compromise the availability of communication services. Attackers can leverage this weakness by constructing malicious WebRTC signaling messages that, when processed by vulnerable browsers, cause the application to terminate unexpectedly or consume excessive system resources. This vulnerability affects not only Firefox browsers but also Thunderbird email clients, which utilize WebRTC for various communication features including video conferencing and instant messaging capabilities. The widespread use of WebRTC across modern web applications means that successful exploitation could impact numerous legitimate user interactions and business-critical communication systems.
Organizations and users should immediately implement mitigation strategies including applying the latest security patches released by Mozilla for Firefox version 149 and Firefox ESR version 140.9, as well as Thunderbird version 149 and Thunderbird version 140.9. Network administrators should consider implementing temporary network-level restrictions that limit WebRTC traffic or filter suspicious signaling messages. From an ATT&CK framework perspective, this vulnerability aligns with techniques categorized under T1499, which involves network disruption and denial-of-service attacks, and T1071, which covers application layer protocol usage for communication. Additional defensive measures should include monitoring for unusual browser process behavior, implementing application whitelisting policies, and conducting regular security assessments of web applications that utilize WebRTC functionality to prevent exploitation of this and similar vulnerabilities.