CVE-2024-5688 Overview
CVE-2024-5688 is a use-after-free vulnerability [CWE-416] in Mozilla Firefox, Firefox ESR, and Thunderbird. The flaw occurs during object transplant operations when garbage collection triggers at a specific time. An attacker who successfully exploits this race condition can cause memory corruption that may lead to arbitrary code execution within the browser process.
The vulnerability affects Firefox versions before 127, Firefox ESR before 115.12, and Thunderbird before 115.12. Mozilla addressed the issue in advisories MFSA-2024-25, MFSA-2024-26, and MFSA-2024-28. Exploitation requires a victim to visit a maliciously crafted web page or process attacker-controlled content.
Critical Impact
Successful exploitation can lead to memory corruption and potential remote code execution in the context of the browser, enabling attackers to compromise user systems through drive-by web content.
Affected Products
- Mozilla Firefox versions before 127
- Mozilla Firefox ESR versions before 115.12
- Mozilla Thunderbird versions before 115.12
Discovery Timeline
- 2024-06-11 - CVE-2024-5688 published to NVD
- 2025-04-04 - Last updated in NVD database
Technical Details for CVE-2024-5688
Vulnerability Analysis
The vulnerability resides in the SpiderMonkey JavaScript engine's object transplant logic. Object transplanting is a mechanism used in browsers to migrate an object's identity across compartments, commonly during cross-origin navigation or wrapper remapping. If a garbage collection (GC) cycle is triggered during the transplant operation, references to the object can become invalidated while still in use.
The resulting use-after-free condition allows an attacker to manipulate freed memory regions. By controlling allocation patterns and timing GC invocations, attackers can place attacker-controlled data into the freed slot. This corruption primitive can be escalated to arbitrary code execution within the content process.
Root Cause
The root cause is improper lifecycle management of objects during transplant operations. The transplant code path does not adequately guard against garbage collection occurring at intermediate states. When GC runs at the precise window, it reclaims memory still referenced by the transplant logic, violating memory safety invariants [CWE-416].
Attack Vector
Exploitation requires network access. An attacker hosts a malicious web page or delivers crafted HTML email content to Thunderbird users. The page uses JavaScript to allocate objects, trigger transplant operations, and force garbage collection at a precise moment. The high attack complexity reflects the timing-dependent nature of the race condition.
No verified public proof-of-concept code is available. The vulnerability is described in Mozilla Bug Report #1895086 and the associated Mozilla security advisories.
Detection Methods for CVE-2024-5688
Indicators of Compromise
- Unexpected child process crashes in firefox.exe or thunderbird.exe, particularly with access violation signatures involving the JavaScript engine.
- Browser crash reports referencing JSObject, JS_TransplantObject, or garbage collection routines in the stack trace.
- Outbound connections from browser processes to unfamiliar domains immediately following visits to untrusted web content.
Detection Strategies
- Inventory installed Firefox, Firefox ESR, and Thunderbird versions across the environment and flag instances below the patched releases.
- Monitor endpoint telemetry for browser process anomalies such as spawning of shells, scripting hosts, or LOLBins from firefox.exe or thunderbird.exe.
- Correlate crash dumps with web proxy logs to identify users who encountered exploit content before the crash.
Monitoring Recommendations
- Enable browser crash reporting and forward telemetry to your SIEM for centralized analysis.
- Track Mozilla security advisories MFSA-2024-25, MFSA-2024-26, and MFSA-2024-28 for related fixes.
- Alert on browser processes performing unusual file writes, registry modifications, or network connections.
How to Mitigate CVE-2024-5688
Immediate Actions Required
- Update Firefox to version 127 or later on all managed endpoints.
- Update Firefox ESR to version 115.12 or later for long-term support deployments.
- Update Thunderbird to version 115.12 or later, especially on systems where users open HTML email from untrusted senders.
- Apply Debian LTS updates referenced in the Debian LTS Security Announcement and Debian LTS Security Update for affected Linux systems.
Patch Information
Mozilla released fixes in Firefox 127, Firefox ESR 115.12, and Thunderbird 115.12. Patch details are available in Mozilla Security Advisory MFSA-2024-25, Mozilla Security Advisory MFSA-2024-26, and Mozilla Security Advisory MFSA-2024-28.
Workarounds
- Configure Thunderbird to render messages as plain text to reduce exposure from HTML email content.
- Restrict JavaScript execution in untrusted contexts using enterprise browser policies where feasible.
- Deploy network-level filtering to block access to known malicious domains and reduce drive-by exploitation risk.
# Verify Firefox version on Linux endpoints
firefox --version
# Verify Thunderbird version
thunderbird --version
# Example apt update for Debian-based systems
sudo apt update && sudo apt install --only-upgrade firefox-esr thunderbird
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
