CVE-2026-2447: Mozilla Firefox Buffer Overflow Vulnerability

CVE-2026-2447 Overview

A heap buffer overflow vulnerability has been identified in the libvpx video codec library used by Mozilla Firefox and Thunderbird. This memory corruption flaw can be exploited when processing specially crafted VP8/VP9 video content, potentially allowing attackers to execute arbitrary code in the context of the affected application.

Critical Impact

Successful exploitation of this heap buffer overflow could enable remote attackers to achieve code execution by luring users to view malicious video content through Firefox or Thunderbird, compromising system confidentiality, integrity, and availability.

Affected Products

• Mozilla Firefox < 147.0.4
• Mozilla Firefox ESR < 140.7.1
• Mozilla Firefox ESR < 115.32.1
• Mozilla Thunderbird < 140.7.2
• Mozilla Thunderbird < 147.0.2

Discovery Timeline

• 2026-02-16 - CVE-2026-2447 published to NVD
• 2026-02-18 - Last updated in NVD database

Technical Details for CVE-2026-2447

Vulnerability Analysis

This vulnerability is classified as CWE-122 (Heap-based Buffer Overflow), a serious memory corruption issue affecting the libvpx component integrated within Mozilla products. The flaw occurs during video decoding operations where improper bounds checking allows writing beyond allocated heap memory boundaries.

The attack requires user interaction—specifically, a victim must navigate to a malicious webpage or open an email containing crafted video content. Once triggered, the overflow condition can corrupt adjacent heap structures, potentially overwriting critical function pointers or metadata that control program execution flow.

The network-accessible nature of this vulnerability combined with the widespread use of Firefox and Thunderbird makes it a significant threat for enterprise and consumer environments alike.

Root Cause

The root cause stems from insufficient bounds validation in the libvpx library when processing VP8 or VP9 video frame data. When parsing certain video structures, the decoder fails to properly verify that input data lengths do not exceed the allocated buffer size, resulting in heap memory being overwritten with attacker-controlled content.

Attack Vector

An attacker can exploit this vulnerability by embedding malicious video content in a webpage, HTML email, or any context where Firefox or Thunderbird will attempt to decode VP8/VP9 video. The attack workflow typically involves:

1. Crafting a malformed VP8/VP9 video file designed to trigger the heap overflow
2. Hosting the malicious content on a web server or embedding it in an email
3. Enticing the victim to visit the webpage or view the email
4. The browser or email client attempts to decode the video, triggering the overflow
5. Memory corruption occurs, potentially leading to arbitrary code execution

No authentication is required to exploit this vulnerability, and exploitation can occur without additional privileges beyond convincing a user to access the malicious content. For detailed technical information, refer to Mozilla Bug Report #2014390.

Detection Methods for CVE-2026-2447

Indicators of Compromise

• Unexpected Firefox or Thunderbird crashes when loading video content, particularly with VP8/VP9 codec usage
• Unusual child processes spawned by Firefox or Thunderbird processes
• Memory access violations or segmentation faults in browser logs related to libvpx
• Network connections to suspicious domains immediately following video playback attempts

Detection Strategies

• Deploy endpoint detection solutions to monitor for abnormal memory allocation patterns in Firefox and Thunderbird processes
• Implement network traffic inspection for potentially malicious video content targeting libvpx codecs
• Configure SIEM rules to correlate browser crashes with subsequent suspicious process activity
• Monitor for exploitation attempts via sandboxed analysis of video content traversing network boundaries

Monitoring Recommendations

• Enable crash reporting for Firefox and Thunderbird to identify potential exploitation attempts
• Configure SentinelOne Deep Visibility to track process ancestry for browser child processes
• Monitor application event logs for repeated crashes or memory-related exceptions in affected versions
• Review web proxy logs for access to domains known to host exploit kits targeting browser vulnerabilities

How to Mitigate CVE-2026-2447

Immediate Actions Required

• Update Mozilla Firefox to version 147.0.4 or later
• Update Mozilla Firefox ESR to version 140.7.1 or 115.32.1 or later (depending on ESR branch)
• Update Mozilla Thunderbird to version 140.7.2 or 147.0.2 or later
• Verify updates have been successfully applied across all managed endpoints

Patch Information

Mozilla has released security patches addressing this vulnerability in the versions listed above. Organizations should prioritize deployment of these updates given the potential for remote code execution.

Review the official Mozilla Security Advisories for complete details:

• Mozilla Security Advisory MFSA-2026-10
• Mozilla Security Advisory MFSA-2026-11

Workarounds

• Disable automatic video playback in Firefox by setting media.autoplay.default to 5 in about:config
• Consider using browser extensions that block automatic media loading until explicitly permitted
• Implement network-level filtering for suspicious video content types where feasible
• Restrict access to untrusted websites through web filtering policies until patches can be deployed

# Verify Firefox version via command line
firefox --version

# Verify Thunderbird version via command line
thunderbird --version

# For enterprise deployment, use policy templates to enforce automatic updates
# Example Firefox policy.json configuration
# {
#   "policies": {
#     "DisableAppUpdate": false,
#     "AppAutoUpdate": true
#   }
# }