Critical Firefox Zero-Interaction Vulnerability Allows Remote Code Execution

Mozilla has urgently released Firefox 139 to address a critical zero-interaction vulnerability that could allow attackers to execute arbitrary code on victims’ systems without any user action beyond normal web browsing. This dangerous flaw affects millions of Firefox users worldwide and requires immediate attention from all organizations using the popular web browser.

Description of the Vulnerability

The vulnerability, tracked as CVE-2025-5262 (MFSA-TMP-2025-0001), is a double-free memory corruption issue located in the libvpx library that Firefox uses for VP8 and VP9 video encoding and decoding in WebRTC communications. The flaw occurs specifically in the vpx_codec_enc_init_multi function when handling failed memory allocations during the encoder initialization process for WebRTC.

The root cause was identified in the vp8e_init() function, where the encoder would take ownership of mr_cfg.mr_low_res_mode_info even if vp8_create_compressor() failed. This created confusion at the call site, as other failures in vp8e_init() did not result in ownership transfer, leading both the caller and vpx_codec_destroy() to free the same memory block, triggering the double-free condition.

The Severity of the Issue

This vulnerability receives a CVSS 3.1 score of 9.8, placing it in the Critical severity category. What makes this particularly dangerous is that it requires absolutely no user interaction beyond visiting a malicious webpage that leverages WebRTC functionality. The vulnerability affects multiple Firefox versions including:

• Firefox versions prior to 139.0
• Firefox ESR versions prior to 128.11
• Firefox ESR versions prior to 115.24

How It Is Exploited

Attackers can exploit this vulnerability simply by forcing victims to load a malicious WebRTC session, such as via a compromised website or phishing link. The exploit could be integrated into web pages that automatically initiate WebRTC connections, triggering the vulnerable code path without any visible indication to the user.

The exploitation process involves:

1. A victim visits a malicious webpage containing WebRTC functionality
2. The webpage triggers the vulnerable libvpx encoder initialization
3. The double-free condition corrupts the browser’s heap memory
4. Attackers can potentially execute arbitrary code on the victim’s system

Who Discovered the Vulnerability

The vulnerability was discovered by Randell Jesup, a Mozilla security engineer and long-time WebRTC developer, during routine code audits. While no specific threat actors have been identified as exploiting this particular flaw, security researchers note that previous vulnerabilities in the libvpx library have been actively exploited in the wild by commercial surveillance vendors.

Who Is at Risk

This vulnerability poses significant risks to:

Individual Users: Anyone using affected Firefox versions for regular web browsing, particularly those who visit websites with video chat functionality, online meeting platforms, or social media sites that use WebRTC.

Enterprise Organizations: Companies using Firefox across their networks face particularly high risk, as attackers could potentially exploit this flaw to gain initial access to corporate systems and move laterally through networks.

Educational Institutions: Schools and universities that rely on Firefox for online learning platforms and video conferencing are at substantial risk.

Government Agencies: Organizations handling sensitive information who use Firefox for daily operations could face targeted attacks exploiting this vulnerability.

Remediation Steps

Mozilla has addressed this critical vulnerability with the following updates released on May 27, 2025:

• Firefox 139
• Firefox ESR 128.11
• Firefox ESR 115.24

Immediate Actions Required:

1. Update Firefox Immediately: Check your Firefox version by going to the Firefox menu, selecting “Help,” and clicking “About Firefox.” The browser will automatically check for updates and prompt you to restart if an update is available.
2. Enable Automatic Updates: Ensure Firefox is configured to automatically install security updates to prevent future exposure to similar vulnerabilities.
3. Enterprise Deployment: IT administrators should prioritize deploying Firefox 139 through centralized management tools across all organizational endpoints.
4. Network Monitoring: Implement monitoring for unusual WebRTC traffic patterns that could indicate exploitation attempts.

 How CinchOps Can Help

At CinchOps, we understand that keeping up with critical security vulnerabilities like this Firefox libvpx flaw can be overwhelming for businesses focused on their core operations. With over three decades of experience delivering complex IT solutions, we’ve seen firsthand how a single unpatched vulnerability can compromise an entire organization’s security posture.

Our comprehensive cybersecurity services can protect your business from threats like this critical Firefox vulnerability:

• Automated Patch Management: We ensure all your browsers and applications receive critical security updates immediately, eliminating the window of vulnerability that attackers exploit
• Endpoint Detection and Response: Deploy advanced monitoring capabilities that continuously watch your systems for suspicious activity, providing real-time protection against malware infections and unauthorized access.
• Employee Security Training: We educate your team about browser-based threats and safe browsing practices to reduce your organization’s overall risk exposure
• Incident Response Planning: Should a security breach occur, our experts provide immediate response and remediation to minimize damage and restore operations quickly
• Continuous Vulnerability Management: We maintain constant vigilance over your technology stack, identifying and addressing security gaps before they become critical risks

Don’t let critical vulnerabilities like CVE-2025-5262 put your business at risk. CinchOps provides the proactive cybersecurity expertise small and medium businesses need to stay protected against sophisticated threats while focusing on what they do best – running their business.

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For Additional Information on this topic: Chrome 137, Firefox 139 Patch High-Severity Vulnerabilities

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