CVE-2024-4777: Mozilla Firefox RCE Vulnerability

CVE-2024-4777 Overview

CVE-2024-4777 covers memory safety bugs identified in Mozilla Firefox 125, Firefox ESR 115.10, and Thunderbird 115.10. Mozilla developers and community members reported evidence of memory corruption in these products. Mozilla assesses that sufficient effort could allow attackers to exploit some of these bugs to run arbitrary code.

The issues are tracked under Mozilla Foundation Security Advisories MFSA-2024-21, MFSA-2024-22, and MFSA-2024-23. The vulnerability classes map to [CWE-787] (out-of-bounds write) and [CWE-416] (use-after-free).

Critical Impact
An attacker who convinces a user to visit a crafted web page can trigger memory corruption in Firefox or Thunderbird and potentially execute arbitrary code in the renderer process.

Affected Products

Mozilla Firefox versions earlier than 126
Mozilla Firefox ESR versions earlier than 115.11
Mozilla Thunderbird versions earlier than 115.11 (Debian Linux 10 packages also affected)

Discovery Timeline

2024-05-14 - CVE-2024-4777 published to the National Vulnerability Database
2025-03-13 - Last updated in NVD database

Technical Details for CVE-2024-4777

Vulnerability Analysis

CVE-2024-4777 aggregates multiple memory safety defects discovered in the Gecko engine shared by Firefox, Firefox ESR, and Thunderbird. Mozilla classifies the issues under [CWE-787] (out-of-bounds write) and [CWE-416] (use-after-free), two memory corruption primitives commonly leveraged for code execution in browsers.

Exploitation requires user interaction, typically loading a malicious page or rendering attacker-controlled HTML email content. Successful exploitation can corrupt heap structures inside the content process and divert execution flow.

Thunderbird is exposed because it reuses the Gecko rendering engine to display messages. Although remote content is disabled by default in mail, scripting can still execute within crafted RSS feeds, calendar invitations, or message previews that involve HTML rendering.

Root Cause

The root cause spans multiple individual bugs in the engine's memory management, referenced in Mozilla's Bugzilla entries 1878199 and 1893340. The defects allow writes outside allocated buffers and access to freed objects, both of which corrupt heap metadata or object pointers used by JavaScript and DOM internals.

Attack Vector

The attack vector is network-based. An attacker hosts a malicious web page or sends an HTML email that triggers the vulnerable code path when rendered. After memory corruption, the attacker can chain the primitive with information leaks and JIT spraying techniques to achieve arbitrary code execution within the content sandbox.

No public exploit or proof-of-concept code has been released for CVE-2024-4777. The vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog. See the Mozilla Bug Report List for technical context.

Detection Methods for CVE-2024-4777

Indicators of Compromise

Firefox or Thunderbird content processes (firefox.exe, thunderbird.exe, or plugin-container) crashing repeatedly with access violations during web browsing or email rendering.
Unexpected child processes spawned by firefox or thunderbird, such as command shells, PowerShell, or scripting interpreters.
Outbound network connections from browser processes to unfamiliar domains immediately after a crash event.

Detection Strategies

Inventory installed Firefox, Firefox ESR, and Thunderbird versions across the fleet and flag any build below 126, 115.11, and 115.11 respectively.
Hunt for browser process crashes correlated with subsequent process creation events using EDR telemetry.
Inspect proxy and DNS logs for users visiting domains known to host browser exploit kits or memory corruption proof-of-concepts.

Monitoring Recommendations

Forward Mozilla crash reporter logs and Windows Error Reporting events to a central log store for analysis.
Monitor parent-child process relationships originating from firefox and thunderbird binaries.
Track update compliance through configuration management tooling to ensure browsers receive Mozilla security updates.

How to Mitigate CVE-2024-4777

Immediate Actions Required

Update Firefox to version 126 or later on all managed endpoints.
Update Firefox ESR to 115.11 or later for environments standardized on the extended support release.
Update Thunderbird to 115.11 or later, including Debian Linux 10 systems patched through Debian LTS advisories.
Restart browser and mail client processes after deployment to ensure the patched binaries are active.

Patch Information

Mozilla released fixes in the advisories MFSA-2024-21, MFSA-2024-22, and MFSA-2024-23. Debian shipped corresponding updates through Debian LTS Advisory #10 and Debian LTS Advisory #12.

Workarounds

Disable JavaScript for untrusted sites using NoScript or enterprise policies where patching is delayed.
Configure Thunderbird to display messages as plain text to reduce HTML rendering exposure.
Restrict browser usage on high-value systems until patches are validated and deployed.

bash

# Verify installed Firefox version on Linux
firefox --version

# Apt-based update for Debian/Ubuntu environments
sudo apt update && sudo apt install --only-upgrade firefox-esr thunderbird

# Windows enterprise policy: force plain text mail in Thunderbird
# %APPDATA%\Thunderbird\Profiles\<profile>\user.js
user_pref("mailnews.display.prefer_plaintext", true);
user_pref("mailnews.display.html_as", 1);