CVE-2024-4771 Overview
CVE-2024-4771 is a use-after-free vulnerability [CWE-416] in Mozilla Firefox versions prior to 126. The flaw stems from a missing memory allocation check. When the allocation fails, the affected code path continues to use a freed or invalid pointer. Attackers can leverage this condition to crash the browser or potentially achieve arbitrary code execution within the Firefox process.
Mozilla addressed the issue in Firefox 126 and documented it in security advisory MFSA-2024-21. The vulnerability is network-reachable through web content rendering and requires no privileges or user interaction beyond visiting a malicious page.
Critical Impact
Successful exploitation can crash Firefox or enable arbitrary code execution in the content process when a user loads attacker-controlled web content.
Affected Products
- Mozilla Firefox versions prior to 126
- Affected component tracked as mozilla:firefox
- Fixed in Firefox 126 per Mozilla Security Advisory MFSA-2024-21
Discovery Timeline
- 2024-05-14 - CVE-2024-4771 published to NVD
- 2025-04-01 - Last updated in NVD database
Technical Details for CVE-2024-4771
Vulnerability Analysis
The vulnerability is a use-after-free condition triggered by a missing allocation check in Firefox. When the runtime attempts to allocate memory and the request fails, the code does not validate the result before continuing. The subsequent operation dereferences or frees a pointer that no longer references valid memory.
Use-after-free conditions in browser engines are a recurring source of exploitable bugs. Attackers can shape the heap to control what occupies the freed memory region. Once the freed pointer is reused, attacker-controlled data influences program flow, leading to crashes or code execution within the content process sandbox.
The issue is reachable through normal web content delivery. Crafted HTML, JavaScript, or related resources can drive the allocation failure path under controlled conditions. Refer to Mozilla Bug Report #1893891 and Mozilla Security Advisory MFSA-2024-21 for vendor-confirmed technical detail.
Root Cause
The root cause is a missing return-value check on a memory allocation function. The affected routine assumes allocation success and proceeds to operate on the returned pointer. When allocation fails under memory pressure or attacker-induced conditions, the code reuses an object that has already been released, producing the use-after-free.
Attack Vector
The attack vector is network-based through web content. An attacker hosts a malicious page or injects crafted content into a trusted site. When a Firefox user before version 126 loads the content, the renderer executes the vulnerable path, triggering the use-after-free. No authentication is required.
No public proof-of-concept code is available for this CVE. The vulnerability is described in prose only; see the linked Mozilla advisory for additional context.
Detection Methods for CVE-2024-4771
Indicators of Compromise
- Unexpected Firefox content-process crashes correlated with browsing activity, particularly MOZ_CRASH or segmentation fault entries in crash telemetry.
- Outbound connections from firefox.exe or firefox to untrusted hosts shortly before crash events.
- Child processes spawned by Firefox that are inconsistent with normal browser behavior.
Detection Strategies
- Inventory Firefox installations across endpoints and flag versions earlier than 126 for remediation.
- Monitor browser crash reports and EDR telemetry for repeated faults in the Firefox content process originating from the same domains.
- Correlate web proxy logs with crash events to identify pages that consistently destabilize the browser.
Monitoring Recommendations
- Enable centralized crash reporting from Firefox endpoints and alert on spikes in content-process termination.
- Track process lineage from firefox parent processes and alert on unexpected child executables.
- Apply network egress monitoring to detect post-exploitation callbacks initiated from a compromised browser session.
How to Mitigate CVE-2024-4771
Immediate Actions Required
- Update Firefox to version 126 or later on all managed endpoints, including ESR builds aligned to the fix.
- Audit unmanaged or user-installed Firefox instances and enforce a minimum supported version through endpoint policy.
- Restrict browsing to required sites for high-risk users until patching completes.
Patch Information
Mozilla released the fix in Firefox 126. Refer to Mozilla Security Advisory MFSA-2024-21 for the official patch announcement and to Mozilla Bug Report #1893891 for the upstream tracking record. Apply the vendor-supplied update through standard Firefox update channels or enterprise deployment tooling.
Workarounds
- No vendor-supplied workaround exists; upgrading to Firefox 126 or later is the required remediation.
- As an interim measure, route browsing through a filtering proxy that blocks untrusted destinations.
- Disable JavaScript on untrusted sites using a content policy extension where operationally feasible.
# Verify installed Firefox version on Linux endpoints
firefox --version
# Example update command on Debian/Ubuntu systems
sudo apt-get update && sudo apt-get install --only-upgrade firefox
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
