CVE-2025-10527: Mozilla Firefox Use-After-Free Vulnerability

CVE-2025-10527 Overview

CVE-2025-10527 is a use-after-free vulnerability in the Graphics: Canvas2D component of Mozilla Firefox and Thunderbird. This memory corruption flaw enables sandbox escape, allowing attackers to potentially break out of the browser's security sandbox and execute code with elevated privileges. The vulnerability affects multiple product lines including Firefox, Firefox ESR, Thunderbird, and Thunderbird ESR, requiring user interaction through a malicious webpage or email content.

Critical Impact

Successful exploitation could allow attackers to escape the browser sandbox and execute arbitrary code outside the confined environment, compromising system security beyond the browser context.

Affected Products

• Mozilla Firefox (versions prior to 143)
• Mozilla Firefox ESR (versions prior to 140.3)
• Mozilla Thunderbird (versions prior to 143 and 140.3)

Discovery Timeline

• September 16, 2025 - CVE-2025-10527 published to NVD
• April 13, 2026 - Last updated in NVD database

Technical Details for CVE-2025-10527

Vulnerability Analysis

This vulnerability is classified as CWE-416 (Use After Free), a memory corruption vulnerability that occurs when a program continues to reference memory after it has been freed. In the context of CVE-2025-10527, the flaw exists within the Graphics: Canvas2D component, which handles HTML5 Canvas 2D rendering operations in Mozilla applications.

The Canvas2D component is responsible for drawing graphics, manipulating images, and rendering visual content on web pages. When processing certain Canvas2D operations, the affected code fails to properly manage memory lifecycle, resulting in a condition where freed memory objects are subsequently accessed. This creates an opportunity for attackers to corrupt memory structures and achieve sandbox escape.

The network-based attack vector requires user interaction—typically viewing a malicious webpage in Firefox or opening malicious content in Thunderbird. Once triggered, the use-after-free condition can be leveraged to execute arbitrary code outside the browser sandbox, effectively bypassing one of the browser's primary security mechanisms.

Root Cause

The root cause of CVE-2025-10527 is improper memory management within the Canvas2D graphics rendering pipeline. Specifically, the vulnerability stems from a failure to properly track object lifetimes during canvas operations, leading to a use-after-free condition where memory that has been deallocated is subsequently dereferenced. This type of error typically occurs when:

1. A memory object is allocated for Canvas2D operations
2. The object is freed during certain rendering or manipulation sequences
3. A dangling pointer to the freed memory remains accessible
4. Subsequent code attempts to use the freed memory, causing corruption

Attack Vector

The attack vector for CVE-2025-10527 is network-based, requiring an attacker to craft malicious web content that triggers the use-after-free condition in the Canvas2D component. The attack flow typically involves:

1. An attacker creates a malicious webpage or email containing specially crafted Canvas2D operations
2. The victim visits the webpage in Firefox or opens malicious content in Thunderbird
3. The malicious Canvas2D code triggers the use-after-free vulnerability
4. The attacker achieves sandbox escape, executing code outside the browser's security boundary
5. From the escaped sandbox, further exploitation can compromise the underlying system

The vulnerability requires no special privileges from the attacker but does require user interaction to trigger.

Detection Methods for CVE-2025-10527

Indicators of Compromise

• Unusual memory allocation patterns or crashes in Firefox/Thunderbird associated with Canvas2D operations
• Unexpected child processes spawned from browser or email client processes
• Evidence of process injection or privilege escalation originating from Mozilla applications
• Browser crash dumps indicating Canvas2D component memory corruption

Detection Strategies

• Monitor for abnormal browser behavior, including unexpected process creation or file system access from sandboxed processes
• Deploy memory integrity monitoring solutions to detect use-after-free exploitation attempts
• Implement application-level logging to capture Canvas2D rendering anomalies
• Configure endpoint detection tools to alert on sandbox escape indicators

Monitoring Recommendations

• Enable crash reporting and analyze browser crash dumps for Canvas2D-related memory corruption
• Monitor network traffic for connections to known malicious domains hosting Canvas2D exploit payloads
• Track application version inventory to identify unpatched Mozilla products in your environment
• Review system logs for unusual process hierarchies involving Firefox or Thunderbird processes

How to Mitigate CVE-2025-10527

Immediate Actions Required

• Update Mozilla Firefox to version 143 or later immediately
• Update Mozilla Firefox ESR to version 140.3 or later
• Update Thunderbird to version 143 or 140.3 or later, depending on your release channel
• Prioritize patching for systems exposed to untrusted web content or email

Patch Information

Mozilla has released security patches addressing this vulnerability across multiple product lines. The fixed versions are:

• Firefox 143 - Standard release channel fix
• Firefox ESR 140.3 - Extended Support Release fix
• Thunderbird 143 - Standard release channel fix
• Thunderbird 140.3 - ESR channel fix

For detailed patch information, refer to the following Mozilla Security Advisories:

• Mozilla Security Advisory MFSA-2025-73
• Mozilla Security Advisory MFSA-2025-75
• Mozilla Security Advisory MFSA-2025-77
• Mozilla Security Advisory MFSA-2025-78

Additional distribution-specific patches are available for Debian systems via Debian LTS Announcement September 2025-20 and Debian LTS Announcement September 2025-26.

Workarounds

• Disable JavaScript execution in untrusted contexts as a temporary measure (note: significantly impacts browsing experience)
• Configure Content Security Policy to restrict Canvas usage on sensitive internal applications
• Consider using alternative browsers temporarily until patches can be applied in high-risk environments
• Block access to known malicious domains at the network perimeter level

# Check Firefox version on Linux systems
firefox --version

# Check Thunderbird version
thunderbird --version

# Force Firefox update on Linux (package manager dependent)
sudo apt update && sudo apt upgrade firefox

# For ESR versions on Debian-based systems
sudo apt update && sudo apt upgrade firefox-esr thunderbird