CVE-2024-3864: Mozilla Firefox RCE Vulnerability

CVE-2024-3864 Overview

CVE-2024-3864 is a memory safety vulnerability affecting Mozilla Firefox 124, Firefox ESR 115.9, and Thunderbird 115.9. Mozilla developers identified memory corruption in these builds during internal testing. The flaw is categorized under [CWE-119], improper restriction of operations within the bounds of a memory buffer. Mozilla assesses that, with sufficient effort, an attacker could leverage the corruption to execute arbitrary code in the context of the affected application. The vulnerability is fixed in Firefox 125, Firefox ESR 115.10, and Thunderbird 115.10.

Critical Impact
Successful exploitation could allow remote attackers to execute arbitrary code by serving a malicious web page or email content to a vulnerable Firefox or Thunderbird client.

Affected Products

Mozilla Firefox versions prior to 125
Mozilla Firefox ESR versions prior to 115.10
Mozilla Thunderbird versions prior to 115.10 (also impacts Debian Linux 10 packages)

Discovery Timeline

2024-04-16 - CVE-2024-3864 published to NVD
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2024-3864

Vulnerability Analysis

The issue is a memory safety bug ([CWE-119]) reported through Mozilla's internal fuzzing and testing pipeline and tracked in Mozilla Bug 1888333. Mozilla observed evidence of memory corruption in the affected builds. Memory corruption in a browser engine commonly leads to remote code execution when an attacker controls the corrupted region or adjacent metadata. Mozilla addressed the issue across three coordinated advisories: MFSA-2024-18 (Firefox 125), MFSA-2024-19 (Firefox ESR 115.10), and MFSA-2024-20 (Thunderbird 115.10).

Root Cause

The root cause is an improper restriction of operations within the bounds of a memory buffer inside the shared Gecko engine code used by Firefox and Thunderbird. Mozilla has not published the specific component or function in the public advisory text. The bug surfaced as memory corruption during instrumented testing, indicating that attacker-influenced inputs can place the heap or stack into an inconsistent state.

Attack Vector

The attack vector is network-based and requires no privileges or user interaction beyond rendering attacker-controlled content. In Firefox, a victim visiting a malicious page can trigger the vulnerable code path. In Thunderbird, the bug is reachable through HTML email content that exercises the same rendering engine. High attack complexity reflects the conditions required to convert the memory corruption into reliable code execution.

No public proof-of-concept code is available for CVE-2024-3864.
Refer to Mozilla Bug 1888333 and MFSA-2024-18/19/20 for technical details.

Detection Methods for CVE-2024-3864

Indicators of Compromise

Firefox or Thunderbird processes crashing with access violations or SIGSEGV shortly after loading web pages or HTML email content
Unexpected child process creation from firefox.exe or thunderbird.exe, such as command shells or scripting hosts
Outbound connections from browser processes to newly registered or low-reputation domains following a crash event

Detection Strategies

Inventory installed Firefox, Firefox ESR, and Thunderbird versions across endpoints and flag any version below 125, 115.10, and 115.10 respectively
Correlate browser crash telemetry (Windows Error Reporting, crashreporter artifacts) with subsequent process or network activity
Apply EDR behavioral rules that alert when browser processes spawn LOLBins (powershell.exe, cmd.exe, wscript.exe, bash)

Monitoring Recommendations

Stream browser and mail client process telemetry into a centralized data lake for cross-event correlation
Track DNS and HTTP egress from firefox and thunderbird processes to identify post-exploitation command-and-control beacons
Monitor for unexpected modifications to user profile directories that may indicate persistence following code execution

How to Mitigate CVE-2024-3864

Immediate Actions Required

Upgrade Firefox to version 125 or later on all managed endpoints
Upgrade Firefox ESR to version 115.10 or later for environments standardized on the extended support release
Upgrade Thunderbird to version 115.10 or later, including Debian-packaged installations referenced in the Debian LTS announcement
Restart browser and mail client sessions after patching to ensure the vulnerable libraries are unloaded

Patch Information

Mozilla released fixes in Firefox 125, Firefox ESR 115.10, and Thunderbird 115.10. Details are published in MFSA-2024-18, MFSA-2024-19, and MFSA-2024-20. Debian users should apply updates documented in the Debian LTS Security Announcement.

Workarounds

Disable HTML rendering in Thunderbird and view messages as plain text to reduce exposure through email content
Restrict outbound web browsing to vetted destinations using a secure web gateway until patches are deployed
Enforce least-privilege user accounts so that any successful exploitation runs without administrative rights

bash

# Verify installed versions on Linux endpoints
firefox --version
firefox-esr --version
thunderbird --version

# Debian/Ubuntu patching
sudo apt update
sudo apt install --only-upgrade firefox-esr thunderbird