CVE-2024-6602: Mozilla Firefox Use-After-Free Flaw

CVE-2024-6602 Overview

CVE-2024-6602 is a memory corruption vulnerability affecting Mozilla Firefox and Thunderbird that stems from a mismatch between allocator and deallocator functions. This type of vulnerability occurs when memory allocated using one memory management routine is freed using an incompatible deallocator, leading to heap corruption and potentially exploitable conditions. Attackers could leverage this flaw to execute arbitrary code in the context of the affected browser or email client.

Critical Impact

This vulnerability allows remote attackers to potentially achieve code execution through memory corruption, affecting both Firefox browsers and Thunderbird email clients across multiple release channels.

Affected Products

• Mozilla Firefox < 128
• Mozilla Firefox ESR < 115.13
• Mozilla Thunderbird < 115.13
• Mozilla Thunderbird < 128

Discovery Timeline

• 2024-07-09 - CVE-2024-6602 published to NVD
• 2025-11-03 - Last updated in NVD database

Technical Details for CVE-2024-6602

Vulnerability Analysis

This vulnerability represents a classic memory management error where the allocator and deallocator used for a memory region do not match. In complex applications like web browsers, multiple memory allocators may be in use (such as the system allocator, jemalloc, or specialized allocators for different subsystems). When memory allocated by one allocator is freed using a different deallocator, the internal heap metadata structures can become corrupted. This corruption can manifest as use-after-free conditions, double-free vulnerabilities, or heap buffer overflows, all of which are highly exploitable for arbitrary code execution.

The network-accessible nature of this vulnerability means attackers can potentially trigger the condition remotely through malicious web content in Firefox or crafted email content in Thunderbird, without requiring user interaction beyond visiting a page or receiving an email.

Root Cause

The root cause is a programming error resulting in mismatched memory allocation and deallocation routines. This typically occurs in codebases with multiple memory management systems where a pointer allocated by one subsystem is inadvertently passed to a deallocation function from a different subsystem. The CWE-94 (Improper Control of Generation of Code) classification suggests this memory corruption could be leveraged to achieve code injection or execution.

Attack Vector

The attack vector is network-based, requiring no privileges or user interaction to exploit. An attacker could craft malicious web content that triggers the allocator/deallocator mismatch when processed by Firefox. Similarly, Thunderbird users could be targeted through specially crafted email messages or embedded content. Upon successful exploitation, attackers could execute arbitrary code with the privileges of the browser or email client process, potentially leading to full system compromise.

The exploitation pathway would involve:

1. Crafting content that triggers the mismatched allocation/deallocation
2. Manipulating the corrupted heap state to achieve controlled memory access
3. Leveraging the memory corruption for code execution or information disclosure

Detection Methods for CVE-2024-6602

Indicators of Compromise

• Unexpected crashes in Firefox or Thunderbird processes, particularly with heap corruption signatures
• Unusual memory allocation patterns or heap metadata corruption in crash dumps
• Process injection or unexpected child processes spawned from browser or email client
• Anomalous network connections originating from Firefox or Thunderbird processes

Detection Strategies

• Monitor for heap corruption or memory-related crash signatures in Firefox and Thunderbird crash logs
• Deploy endpoint detection rules to identify unusual process behavior from Mozilla applications
• Implement network monitoring for connections to known malicious infrastructure from browser processes
• Utilize memory forensics tools to detect heap corruption artifacts during incident response

Monitoring Recommendations

• Enable crash reporting and analyze crash telemetry for memory corruption indicators
• Implement application whitelisting to detect unauthorized code execution from browser processes
• Monitor process creation events for suspicious child processes spawned by Firefox or Thunderbird
• Deploy behavioral analysis solutions to detect post-exploitation activity

How to Mitigate CVE-2024-6602

Immediate Actions Required

• Update Mozilla Firefox to version 128 or later immediately
• Update Mozilla Firefox ESR to version 115.13 or later
• Update Mozilla Thunderbird to version 128 or later (or 115.13 for ESR)
• Verify all Mozilla products in your environment are on patched versions

Patch Information

Mozilla has released security patches addressing this vulnerability across multiple product lines. The following security advisories contain detailed patch information:

• Mozilla Security Advisory MFSA-2024-29 - Firefox 128 release
• Mozilla Security Advisory MFSA-2024-30 - Firefox ESR 115.13 release
• Mozilla Security Advisory MFSA-2024-31 - Thunderbird 115.13 release
• Mozilla Security Advisory MFSA-2024-32 - Thunderbird 128 release

Additional technical details are available in Mozilla Bug Report #1895032. Debian-based distributions should also reference the Debian LTS Announcement for package updates.

Workarounds

• Limit browsing to trusted websites until patches can be applied
• Consider using alternative browsers temporarily for high-risk activities
• Disable JavaScript execution where possible to reduce attack surface
• Implement network-level content filtering to block known exploit delivery mechanisms

# Verify Firefox version from command line
firefox --version

# Verify Thunderbird version from command line
thunderbird --version

# On Linux, check installed package version (Debian/Ubuntu)
apt list --installed | grep -E "(firefox|thunderbird)"