CVE-2024-3865: Mozilla Firefox RCE Vulnerability

CVE-2024-3865 Overview

CVE-2024-3865 is a memory safety vulnerability affecting Mozilla Firefox versions prior to 125. Mozilla developers and community members reported memory safety bugs present in Firefox 124. Several of these bugs showed evidence of memory corruption. Mozilla assessed that with sufficient effort, an attacker could exploit some of these flaws to run arbitrary code in the browser process.

The vulnerability is classified under [CWE-119] (Improper Restriction of Operations within the Bounds of a Memory Buffer). Exploitation requires a user to load attacker-controlled web content, making drive-by attacks via malicious or compromised websites the primary delivery method.

Critical Impact
Successful exploitation could allow remote attackers to corrupt memory and potentially execute arbitrary code within the Firefox process, leading to full browser compromise.

Affected Products

Mozilla Firefox versions earlier than 125
Firefox 124 (specifically called out in the advisory)
Builds tracked in Bugzilla entries 1881076, 1884887, 1885359, and 1889049

Discovery Timeline

2024-04-16 - CVE-2024-3865 published to NVD via Mozilla Security Advisory MFSA-2024-18
2025-05-01 - Last updated in NVD database

Technical Details for CVE-2024-3865

Vulnerability Analysis

The advisory groups multiple memory safety defects discovered during the Firefox 124 release cycle. Mozilla's internal fuzzing infrastructure and contributors identified the issues, and several demonstrated observable memory corruption during testing. The vulnerability class covers improper restriction of operations within memory buffer boundaries, which encompasses out-of-bounds reads and writes, use-after-free conditions, and heap corruption.

Memory corruption in a browser rendering engine has broad consequences. The browser parses untrusted HTML, CSS, JavaScript, image, font, and media content from arbitrary origins. Any parser or runtime component touching this content becomes an attack surface. Attackers who control even a small primitive can chain it into reliable code execution using modern browser exploitation techniques.

Root Cause

Mozilla did not publish per-bug root-cause analysis in the public advisory. The referenced Mozilla Bug Reports remain restricted while downstream distributions ship the fix. The shared root condition is improper memory buffer handling tracked under [CWE-119], spanning multiple components shipped in Firefox 124.

Attack Vector

The attack vector is network-based and requires no authentication or user interaction beyond visiting a page. An attacker hosts crafted web content on a controlled domain or injects it through a compromised site, malicious advertisement, or iframe. When Firefox parses the content, the corrupted memory state can be steered toward arbitrary code execution within the renderer or content process sandbox.

No public proof-of-concept exploit is available. The vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog, and no in-the-wild exploitation has been reported.

See the Mozilla Security Advisory MFSA-2024-18 for the full technical disclosure.

Detection Methods for CVE-2024-3865

Indicators of Compromise

Firefox processes spawning unexpected child processes such as cmd.exe, powershell.exe, or shell interpreters on Linux and macOS
Unexpected Firefox crashes with exception codes indicating access violations or heap corruption in renderer processes
Outbound connections from firefox.exe to low-reputation or newly registered domains immediately after page loads
Creation of new files in user-writable persistence locations by the Firefox process tree

Detection Strategies

Inventory installed Firefox versions across the fleet and flag any build numbered earlier than 125
Monitor browser telemetry and crash reports for renderer process termination patterns consistent with memory corruption
Correlate web proxy logs with endpoint process activity to surface drive-by exploitation attempts

Monitoring Recommendations

Forward browser process telemetry, child process creation events, and network connections to a centralized analytics platform
Alert on Firefox processes loading unsigned modules or writing executables to disk
Track DNS and HTTP requests to known exploit kit infrastructure and newly observed domains referenced by Firefox sessions

How to Mitigate CVE-2024-3865

Immediate Actions Required

Upgrade all Firefox installations to version 125 or later without delay
Apply the corresponding ESR or extended support updates supplied by your Linux distribution or packaging system
Enforce automatic updates for Firefox through enterprise policy where feasible
Verify the deployed version after patching by checking about:support or the package manager

Patch Information

Mozilla released the fix in Firefox 125. Details and links to the patched builds are provided in Mozilla Security Advisory MFSA-2024-18. Linux distributions and downstream vendors have published corresponding security updates.

Workarounds

Restrict Firefox use to trusted sites until patching is complete, using web filtering or proxy allowlists
Disable JavaScript on untrusted origins through enterprise policy or NoScript-style controls to reduce the exploitable surface
Run Firefox under standard user accounts without administrative privileges to limit post-exploitation impact

bash

# Verify Firefox version on Linux endpoints
firefox --version

# Example: enforce minimum version via Debian/Ubuntu package pinning
apt-cache policy firefox
sudo apt-get update && sudo apt-get install --only-upgrade firefox

# Example: enterprise policy snippet (policies.json) to enforce auto-updates
# Place at /etc/firefox/policies/policies.json or %ProgramFiles%\Mozilla Firefox\distribution\
# {
#   "policies": {
#     "DisableAppUpdate": false,
#     "AppAutoUpdate": true
#   }
# }