The Vulnerability Explained

The vulnerability, discovered by Mozilla developer Andrew McCreight, is described as an “incorrect handle could lead to sandbox escapes” affecting Firefox on Windows systems. Mozilla has released Firefox 136.0.4 to patch this critical security vulnerability that can let attackers escape the web browser’s sandbox on Windows systems.

The flaw stems from mismanagement of system handles that inadvertently grants elevated access to unprivileged child processes, allowing them to escape the browser sandbox. As Mozilla noted in its security advisory, “Attackers were able to confuse the parent process into leaking handles to unprivileged child processes leading to a sandbox escape.”

This vulnerability is similar to a Chrome zero-day (CVE-2025-2783) that was exploited in attacks and patched by Google earlier this week. According to Mozilla, “Following the sanbdox escape in CVE-2025-2783, various Firefox developers identified a similar pattern in our IPC code.”

  Affected Versions and Platforms

The security vulnerability affects Firefox and Firefox ESR (Extended Support Release) on Windows platforms. Linux and macOS users are not affected by this vulnerability.

  Risk Assessment

The potential impact of this vulnerability is severe for several reasons:

Sandboxing is a cornerstone of modern browser security, isolating web content from critical system components. A sandbox escape undermines this barrier, enabling attackers to pivot from browser compromise to full system access, especially in targeted attacks involving malicious web content or drive-by downloads.

While there is no evidence that CVE-2025-2857 has been exploited in the wild, the vulnerability’s nature—combined with recent APT activity—makes it a critical patching priority.

  Remediation Steps

To protect your systems from this vulnerability, take the following actions immediately:

1. Update your Firefox browser to version 136.0.4, or if you’re using Firefox ESR, update to versions 115.21.1 or 128.8.1.
2. Mozilla has patched the flaw across all supported branches:
   • Firefox 136.0.4
   • Firefox ESR 115.21.1
   • Firefox ESR 128.8.1
3. Consider implementing network-level protections to filter potentially malicious web content.
4. Ensure your organization has an effective patch management system in place to quickly address critical vulnerabilities like this one.

 How CinchOps Can Help Secure Your Business

In today’s threat environment, vulnerabilities like CVE-2025-2857 highlight the critical need for proactive security management. CinchOps provides comprehensive security solutions that can help protect your organization:

• Vulnerability Management: Our automated scanning tools can identify unpatched browsers and other vulnerable software across your enterprise.
• Patch Management: We streamline the patching process to ensure critical security updates are deployed quickly across your organization.
• Zero-Day Protection: Our advanced threat protection services can detect and block exploitation attempts even before patches are available.
• Security Monitoring: Our 24/7 security operations center monitors for suspicious activities that may indicate exploitation attempts.
• User Awareness Training: We provide training to help your employees recognize and avoid potential web-based threats.

Discover more about our enterprise-grade and business protecting cybersecurity services on our Cybersecurity page.

Don’t wait for an attack to occur. Contact CinchOps today to ensure your organization is protected against critical vulnerabilities like CVE-2025-2857 and other emerging threats.

FREE CYBERSECURITY ASSESSMENT