CVE-2024-4764: Mozilla Firefox Use-After-Free Vulnerability

CVE-2024-4764 Overview

CVE-2024-4764 is a use-after-free vulnerability in Mozilla Firefox's WebRTC implementation. Multiple WebRTC threads could simultaneously claim a newly connected audio input device, leading to a race condition that results in use-after-free memory corruption. This vulnerability allows attackers to potentially execute arbitrary code or cause denial of service conditions through network-based attacks without requiring user interaction.

Critical Impact

This use-after-free vulnerability in Firefox's WebRTC audio handling could allow remote attackers to execute arbitrary code or crash the browser, potentially compromising user systems through malicious web content.

Affected Products

• Mozilla Firefox versions prior to 126
• Mozilla Firefox (all platforms)
• Mozilla Firefox standard release channel

Discovery Timeline

• 2024-05-14 - CVE CVE-2024-4764 published to NVD
• 2025-04-01 - Last updated in NVD database

Technical Details for CVE-2024-4764

Vulnerability Analysis

This vulnerability is classified as CWE-416 (Use After Free), a memory corruption vulnerability that occurs when a program continues to use a pointer after the memory it references has been freed. In the context of Firefox's WebRTC implementation, the flaw exists in the audio input device handling mechanism.

When a new audio input device is connected to a system running Firefox with an active WebRTC session, multiple threads within the WebRTC subsystem may simultaneously attempt to claim ownership of the newly available audio resource. This race condition creates a scenario where one thread may free the audio input object while another thread still holds a reference to it, leading to use-after-free conditions.

Exploitation of this vulnerability could allow an attacker to corrupt memory, potentially leading to arbitrary code execution within the context of the Firefox process. Since WebRTC functionality is commonly used for video conferencing, voice calls, and real-time communication features, websites with legitimate WebRTC usage could inadvertently trigger this vulnerability, or malicious sites could deliberately exploit it.

Root Cause

The root cause of CVE-2024-4764 lies in improper synchronization between WebRTC threads when handling newly connected audio input devices. The lack of proper mutex locks or atomic operations when multiple threads attempt to claim the same audio resource creates a classic race condition vulnerability. When the audio input object is deallocated by one thread while another thread still maintains a dangling pointer to it, subsequent operations on that pointer result in use-after-free conditions.

Attack Vector

The attack vector for this vulnerability is network-based. An attacker can exploit this vulnerability by:

1. Hosting a malicious website that initiates WebRTC connections
2. Triggering audio input device enumeration or connection events
3. Exploiting the race condition when the victim connects or reconnects an audio device
4. Leveraging the use-after-free condition to achieve code execution or crash the browser

The vulnerability can be exploited without any user credentials and requires no direct user interaction beyond visiting a malicious webpage with WebRTC capabilities.

The vulnerability manifests in the WebRTC audio device handling threads where concurrent access to newly connected audio inputs is not properly synchronized. For detailed technical information, refer to the Mozilla Bug Report #1879093 and the Mozilla Security Advisory MFSA-2024-21.

Detection Methods for CVE-2024-4764

Indicators of Compromise

• Unexpected Firefox browser crashes, particularly during WebRTC-enabled web sessions or video/audio calls
• Memory corruption errors or segmentation faults in Firefox process logs
• Unusual WebRTC connection attempts from untrusted or suspicious websites
• Anomalous audio device enumeration requests in browser activity logs

Detection Strategies

• Monitor for Firefox process crashes with stack traces indicating WebRTC audio subsystem involvement
• Implement browser-level logging to track WebRTC session initialization and audio device handling events
• Deploy endpoint detection solutions to identify use-after-free exploitation patterns in browser processes
• Use memory sanitizers (ASan, MSan) in testing environments to detect memory corruption attempts

Monitoring Recommendations

• Enable crash reporting and telemetry in Firefox to identify potential exploitation attempts
• Monitor network traffic for suspicious WebRTC signaling patterns from untrusted origins
• Implement Content Security Policy headers to restrict WebRTC usage to trusted domains
• Deploy SentinelOne Singularity platform to detect memory corruption exploitation attempts in real-time

How to Mitigate CVE-2024-4764

Immediate Actions Required

• Upgrade Mozilla Firefox to version 126 or later immediately
• Review and restrict WebRTC permissions in Firefox settings until patching is complete
• Consider temporarily disabling WebRTC in about:config by setting media.peerconnection.enabled to false
• Implement network-level blocking for known malicious domains targeting this vulnerability

Patch Information

Mozilla has addressed this vulnerability in Firefox version 126. Users and organizations should update to the latest version of Firefox to receive the security fix. The patch addresses the race condition in WebRTC audio input handling by implementing proper thread synchronization mechanisms.

For detailed patch information, see:

• Mozilla Security Advisory MFSA-2024-21
• Mozilla Bug Report #1879093

Workarounds

• Disable WebRTC functionality in Firefox by navigating to about:config and setting media.peerconnection.enabled to false
• Use browser extensions that block or control WebRTC connections from untrusted sites
• Implement Content Security Policy headers on internal web applications to prevent unauthorized WebRTC usage
• Consider using an alternative browser until Firefox can be updated to version 126 or later

# Firefox WebRTC disable configuration
# Navigate to about:config in Firefox and set:
# media.peerconnection.enabled = false
# media.navigator.enabled = false

# For enterprise deployment, use policies.json:
# Place in Firefox installation directory/distribution/
cat > /usr/lib/firefox/distribution/policies.json << EOF
{
  "policies": {
    "Preferences": {
      "media.peerconnection.enabled": {
        "Value": false,
        "Status": "locked"
      }
    }
  }
}
EOF