Mozilla Firefox and Thunderbird WebRTC Undefined Behavior Vulnerability (CVE-2026-4705)

CVE-2026-4705 details an undefined behavior vulnerability within the WebRTC signaling component of Mozilla Firefox and Thunderbird. Specifically, Firefox versions prior to 149, Firefox ESR versions prior to 140.9, Thunderbird versions prior to 149, and Thunderbird ESR versions prior to 140.9 are affected. This vulnerability could potentially allow an attacker to execute arbitrary code due to unexpected behavior when handling WebRTC signaling, making it critical for organizations relying on these applications to address this issue promptly. The vulnerability was reported on March 24, 2026.

Attack Chain

1. An attacker crafts a malicious web page or email containing specially crafted WebRTC signaling data.
2. A user opens the malicious web page in a vulnerable version of Firefox or Thunderbird or views the malicious email.
3. The vulnerable application processes the malicious WebRTC signaling data.
4. Due to the undefined behavior in the WebRTC signaling component, the application enters an unexpected state.
5. This unexpected state allows the attacker to potentially corrupt memory or execute arbitrary code.
6. The attacker leverages the arbitrary code execution to gain control of the affected system.
7. The attacker may then install malware, steal sensitive data, or pivot to other systems on the network.

Impact

Successful exploitation of CVE-2026-4705 could allow a remote attacker to execute arbitrary code on a vulnerable system. Given the widespread use of Firefox and Thunderbird, a successful exploit could have a significant impact, potentially affecting a large number of users and organizations. Exploitation could lead to data breaches, system compromise, and further malicious activities.

Recommendation

• Upgrade Firefox to version 149 or later to patch CVE-2026-4705.
• Upgrade Firefox ESR to version 140.9 or later to patch CVE-2026-4705.
• Upgrade Thunderbird to version 149 or later to patch CVE-2026-4705.
• Upgrade Thunderbird ESR to version 140.9 or later to patch CVE-2026-4705.
• Deploy the Sigma rule Detect_CVE_2026_4705_Crash to monitor for potential exploitation attempts based on unexpected crashes in Firefox or Thunderbird related to WebRTC.