CVE-2024-7522: Mozilla Firefox Use-After-Free Vulnerability

CVE-2024-7522 Overview

CVE-2024-7522 is an out-of-bounds read vulnerability in Mozilla Firefox, Firefox ESR, and Thunderbird. The flaw exists in editor code that failed to validate an attribute value before processing. An attacker can exploit the issue by enticing a user to visit a malicious web page or open crafted content, triggering memory disclosure or memory corruption in the browser process. The vulnerability affects Firefox versions prior to 129, Firefox ESR prior to 115.14 and 128.1, and Thunderbird prior to 115.14 and 128.1. Mozilla addressed the issue in advisories MFSA-2024-33 through MFSA-2024-38.

Critical Impact

Successful exploitation enables an attacker to read out-of-bounds memory from the browser process via a crafted page, potentially leading to information disclosure or chained memory corruption.

Affected Products

• Mozilla Firefox versions prior to 129
• Mozilla Firefox ESR versions prior to 115.14 and prior to 128.1
• Mozilla Thunderbird versions prior to 115.14 and prior to 128.1

Discovery Timeline

• 2024-08-06 - CVE-2024-7522 published to NVD
• 2024-08-12 - Last updated in NVD database

Technical Details for CVE-2024-7522

Vulnerability Analysis

The vulnerability is classified as an out-of-bounds read [CWE-125] in the editor component shared across Firefox, Firefox ESR, and Thunderbird. The editor code processes an attribute value without performing the required bounds check on its contents. When the unchecked value is used as an offset or length parameter during subsequent memory operations, the engine reads memory outside the bounds of the intended buffer.

Exploitation requires user interaction, such as visiting a malicious web page in Firefox or viewing crafted HTML content in Thunderbird. The attack is remotely deliverable over the network and does not require authentication. Mozilla rates the bug as high severity, and the affected attribute-handling path is reachable from untrusted web content rendered by the editor.

Root Cause

The root cause is missing validation of an attribute value within editor code paths. Without the bounds check, the engine trusts attacker-controlled input when computing memory offsets, causing the read to extend beyond the allocated object. Mozilla tracked the underlying defect in Mozilla Bug Report #1906727.

Attack Vector

An attacker hosts a malicious HTML document or sends a crafted email that triggers the vulnerable editor code path when rendered. The victim must interact with the content by loading the page or opening the message. Once the unchecked attribute value reaches the affected code path, the process reads adjacent heap memory, which can leak sensitive data or be combined with other primitives to escalate to code execution.

No verified public exploit code or proof-of-concept is currently available. Refer to the Mozilla Security Advisory MFSA-2024-33 for vendor-side technical context.

Detection Methods for CVE-2024-7522

Indicators of Compromise

• Unexpected crashes of firefox.exe, firefox-bin, or thunderbird.exe correlated with browsing or email rendering events.
• Browser telemetry showing renderer process restarts after loading external HTML or message content.
• Outbound connections from end-user hosts to newly observed domains hosting HTML payloads followed by browser process anomalies.

Detection Strategies

• Inventory installed browser and mail client versions and flag endpoints running Firefox below 129, Firefox ESR below 115.14 or 128.1, or Thunderbird below 115.14 or 128.1.
• Monitor process telemetry for anomalous child processes spawned by Firefox or Thunderbird following content rendering.
• Apply web proxy detections for known malicious domains and inspect HTML payloads that include suspicious editor-targeting attributes.

Monitoring Recommendations

• Forward browser and mail client crash logs to a central logging platform for correlation with web activity.
• Track software inventory drift to identify hosts that fall behind on Mozilla security updates.
• Alert on credential or session token exfiltration patterns following browser anomalies, as memory disclosure can leak in-process secrets.

How to Mitigate CVE-2024-7522

Immediate Actions Required

• Update Firefox to version 129 or later on all managed endpoints.
• Update Firefox ESR to 115.14 or 128.1 and Thunderbird to 115.14 or 128.1 across desktop and mail infrastructure.
• Restart browser and mail client processes after patching to ensure the vulnerable code is unloaded.
• Validate patch deployment with software inventory queries and remediate non-compliant hosts.

Patch Information

Mozilla published fixes in MFSA-2024-33, MFSA-2024-34, MFSA-2024-35, MFSA-2024-37, and MFSA-2024-38. The corresponding fixed builds are Firefox 129, Firefox ESR 115.14, Firefox ESR 128.1, Thunderbird 115.14, and Thunderbird 128.1.

Workarounds

• Restrict execution of untrusted HTML content in Thunderbird by disabling remote content and rendering messages as plain text.
• Enforce web filtering policies that block access to unknown or low-reputation domains until patching completes.
• Use managed browser policies to enable automatic updates so future Mozilla advisories are applied without delay.

# Verify installed Firefox version on Linux endpoints
firefox --version

# Verify Thunderbird version
thunderbird --version

# Example: enforce automatic updates via Firefox enterprise policy (policies.json)
# {
#   "policies": {
#     "DisableAppUpdate": false,
#     "AppAutoUpdate": true
#   }
# }