CVE-2025-3028: Mozilla Firefox Use-After-Free Vulnerability

CVE-2025-3028 Overview

CVE-2025-3028 is a use-after-free vulnerability affecting Mozilla Firefox and Thunderbird browsers. The flaw occurs when JavaScript code executes during document transformation using the XSLTProcessor component. This memory corruption vulnerability could allow attackers to manipulate freed memory, potentially leading to integrity and availability impacts on affected systems.

Critical Impact
Attackers can exploit this use-after-free condition through crafted web content, potentially compromising system integrity and causing denial of service conditions in Mozilla Firefox and Thunderbird.

Affected Products

Mozilla Firefox versions prior to 137
Mozilla Firefox ESR versions prior to 115.22 and 128.9
Mozilla Thunderbird versions prior to 137 and 128.9

Discovery Timeline

April 1, 2025 - CVE-2025-3028 published to NVD
November 3, 2025 - Last updated in NVD database

Technical Details for CVE-2025-3028

Vulnerability Analysis

This use-after-free vulnerability (CWE-416) exists within the XSLTProcessor component of Mozilla Firefox and Thunderbird. The flaw is triggered when JavaScript code runs during the transformation of an XML document. During this transformation process, memory that has been freed can be subsequently accessed, creating a use-after-free condition.

Use-after-free vulnerabilities occur when a program continues to use a pointer after the memory it references has been deallocated. In this case, the XSLTProcessor's handling of JavaScript execution during document transformation creates a race condition where memory management becomes inconsistent. An attacker could craft a malicious web page or email that exploits this timing issue to reference freed memory.

The vulnerability is network-accessible, requiring no user interaction or special privileges to exploit, making it particularly concerning for browser-based attack scenarios.

Root Cause

The root cause of CVE-2025-3028 lies in improper memory lifecycle management within the XSLTProcessor component. When JavaScript code executes during an XSLT transformation, the processor fails to properly track the state of allocated memory objects. This allows a scenario where memory is freed while still being referenced by the transformation process, leading to the use-after-free condition.

The XSLTProcessor is designed to transform XML documents using XSLT stylesheets, but its integration with the JavaScript engine creates complexity in memory management. The vulnerability arises from the asynchronous nature of JavaScript execution and the synchronous expectations of the XSLT transformation pipeline.

Attack Vector

The attack vector for CVE-2025-3028 is network-based. An attacker could exploit this vulnerability by:

Crafting a malicious web page containing specially designed XML content with an XSLT stylesheet
Including JavaScript code that triggers during the XSLT transformation
Manipulating the timing of memory allocation and deallocation to create the use-after-free condition
Potentially leveraging the freed memory access to modify data integrity or cause application crashes

For Thunderbird users, the attack could be delivered through a malicious email containing crafted content that triggers the vulnerable code path when rendered.

Detection Methods for CVE-2025-3028

Indicators of Compromise

Unexpected Firefox or Thunderbird crashes during page rendering or email viewing
Memory access violations in browser crash dumps referencing XSLTProcessor components
Unusual XSLT transformation errors in browser console logs
Abnormal memory consumption patterns when processing XML/XSLT content

Detection Strategies

Monitor browser application logs for XSLTProcessor-related exceptions and crashes
Implement endpoint detection rules to identify exploitation attempts targeting Mozilla products
Deploy network-based detection for malicious XSLT content delivery
Review crash telemetry for patterns consistent with use-after-free exploitation

Monitoring Recommendations

Enable crash reporting and telemetry in Firefox and Thunderbird deployments
Monitor for unusual JavaScript execution patterns during document transformations
Implement application-level logging for XSLT processing activities
Review security event logs for browser exploitation indicators

How to Mitigate CVE-2025-3028

Immediate Actions Required

Update Mozilla Firefox to version 137 or later immediately
Update Mozilla Firefox ESR to version 115.22 or 128.9 or later
Update Mozilla Thunderbird to version 137 or 128.9 or later
Prioritize updates for systems that process untrusted web content or emails

Patch Information

Mozilla has released security patches addressing this vulnerability across multiple product versions. Detailed patch information is available through the official Mozilla Security Advisories:

Linux users should also review the Debian LTS Announcement April 2025 for distribution-specific patch availability. Technical details are tracked in Mozilla Bug Report #1941002.

Workarounds

Disable JavaScript execution for untrusted content where feasible
Configure email clients to display messages in plain text mode
Implement content security policies to restrict XSLT processing from untrusted sources
Use network-level filtering to block known malicious content patterns

bash

# Firefox configuration workaround (about:config)
# Disable XSLT processing as temporary mitigation
# Note: This may break legitimate functionality
user_pref("dom.xslt.enabled", false);