CVE-2024-5695: Mozilla Firefox Buffer Overflow Vulnerability

CVE-2024-5695 Overview

CVE-2024-5695 is a memory corruption vulnerability affecting Mozilla Firefox's probabilistic heap checker component. When an out-of-memory (OOM) condition occurs at a specific point during heap allocations, the vulnerability can trigger an assertion failure. In rarer circumstances, this condition may lead to memory corruption, potentially enabling remote code execution or denial of service attacks against affected browsers.

Critical Impact

This vulnerability could allow attackers to cause memory corruption in Firefox browsers, potentially leading to arbitrary code execution or browser crashes when users visit malicious web pages.

Affected Products

• Mozilla Firefox versions prior to 127
• All platforms running vulnerable Firefox versions (Windows, macOS, Linux)

Discovery Timeline

• 2024-06-11 - CVE-2024-5695 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2024-5695

Vulnerability Analysis

This vulnerability resides in Firefox's probabilistic heap checker, a memory debugging and validation component used during runtime. The flaw occurs when memory allocation operations fail due to an out-of-memory condition at a specific critical point in the heap checker's operation.

Under normal circumstances, an OOM condition would trigger a controlled assertion failure, causing the application to terminate gracefully. However, due to improper handling of this edge case, the vulnerability creates a race condition where memory state becomes inconsistent before the assertion can properly halt execution. In rare but exploitable scenarios, this inconsistency leads to memory corruption.

The vulnerability is classified as CWE-787 (Out-of-bounds Write), indicating that the memory corruption manifests as writes to memory locations outside intended boundaries when the OOM condition is triggered.

Root Cause

The root cause stems from inadequate error handling in the probabilistic heap checker when processing memory allocation failures. The heap checker fails to properly validate memory state before proceeding with operations that assume successful allocation. When an allocation fails at the precise moment during a heap validation check, the component continues execution with invalid memory references, corrupting adjacent heap structures.

Attack Vector

An attacker can exploit this vulnerability through network-based attacks by crafting malicious web content designed to exhaust browser memory resources at strategic moments. The attack scenario involves:

1. Luring a victim to a malicious website
2. Triggering excessive memory allocations through JavaScript or resource-heavy content
3. Timing the OOM condition to coincide with heap checker operations
4. Exploiting the resulting memory corruption for code execution or denial of service

The vulnerability is exploitable remotely without requiring authentication or user interaction beyond visiting a malicious page. Due to the timing requirements, successful exploitation may require multiple attempts, but the network accessibility and lack of required privileges make this a significant risk.

The vulnerability mechanism involves improper handling of memory allocation failures within the heap checker component. When the probabilistic heap checker performs memory validation, it makes allocation requests that can fail under memory pressure. The failure path does not properly account for partially initialized state, leading to the assertion trigger or memory corruption. For complete technical details, refer to the Mozilla Bug Report #1895579.

Detection Methods for CVE-2024-5695

Indicators of Compromise

• Unexpected Firefox browser crashes with heap-related error messages in crash reports
• Abnormal memory consumption patterns in Firefox processes before application failure
• Crash dump files indicating heap corruption or assertion failures in memory allocation routines
• System logs showing Firefox termination due to memory violations

Detection Strategies

• Monitor Firefox crash telemetry for heap checker-related assertion failures
• Implement endpoint detection rules to identify abnormal memory allocation patterns in browser processes
• Deploy network inspection to detect known patterns of memory exhaustion attacks targeting browsers
• Utilize behavioral analysis to identify web pages attempting rapid memory allocation sequences

Monitoring Recommendations

• Enable Firefox crash reporting and analyze crash signatures for CVE-2024-5695 patterns
• Monitor memory usage metrics for Firefox processes to detect potential exploitation attempts
• Track outbound crash report submissions to Mozilla for correlating vulnerability exploitation
• Implement application-layer logging to capture browser stability issues across the organization

How to Mitigate CVE-2024-5695

Immediate Actions Required

• Update Mozilla Firefox to version 127 or later immediately across all systems
• Enable automatic browser updates to ensure timely deployment of security patches
• Consider temporary restriction of untrusted web browsing until patches are deployed
• Review crash logs for any indication of prior exploitation attempts

Patch Information

Mozilla has addressed this vulnerability in Firefox version 127. The fix properly handles out-of-memory conditions in the probabilistic heap checker to prevent both assertion failures and memory corruption scenarios.

For complete patch details, see the Mozilla Security Advisory MFSA-2024-25.

Organizations should prioritize deployment of Firefox 127+ to eliminate exposure to this vulnerability. Enterprise environments using Firefox ESR should verify their version includes the necessary fixes.

Workarounds

• Limit browsing to trusted websites until Firefox can be updated to a patched version
• Consider using alternative browsers temporarily for high-risk browsing activities
• Implement browser isolation technologies to contain potential exploitation
• Configure content security policies to restrict memory-intensive operations on untrusted sites

# Verify Firefox version on Linux/macOS
firefox --version

# For enterprise deployment, ensure minimum version 127
# Update Firefox via package manager (example for Ubuntu/Debian)
sudo apt update && sudo apt install firefox

# For Windows, check version via command line
"C:\Program Files\Mozilla Firefox\firefox.exe" --version | more