CVE-2026-2804
📋 TL;DR
A use-after-free vulnerability in Firefox's WebAssembly JavaScript component allows attackers to execute arbitrary code by manipulating freed memory. This affects all Firefox users running versions below 148, potentially enabling remote code execution through malicious web content.
💻 Affected Systems
- Mozilla Firefox
📦 What is this software?
Firefox by Mozilla
Thunderbird by Mozilla
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to full system compromise, data theft, or ransomware deployment.
Likely Case
Browser crash or arbitrary code execution within browser context, potentially stealing session cookies or credentials.
If Mitigated
Limited impact if browser sandboxing works properly, possibly just browser crash.
🎯 Exploit Status
Use-after-free vulnerabilities typically require precise timing and memory manipulation, but WebAssembly components are commonly targeted.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Firefox 148
Vendor Advisory: https://www.mozilla.org/security/advisories/mfsa2026-13/
Restart Required: Yes
Instructions:
1. Open Firefox. 2. Click menu → Help → About Firefox. 3. Allow automatic update to version 148. 4. Restart Firefox when prompted.
🔧 Temporary Workarounds
Disable WebAssembly
allTemporarily disable WebAssembly execution in Firefox to prevent exploitation.
about:config → Set javascript.options.wasm to false
Use NoScript Extension
allBlock JavaScript execution on untrusted sites to prevent malicious WebAssembly loading.
Install NoScript extension from addons.mozilla.org
🧯 If You Can't Patch
- Restrict browser use to trusted websites only
- Implement application whitelisting to prevent unauthorized code execution
🔍 How to Verify
Check if Vulnerable:
Check Firefox version in about:firefox or Help → About Firefox.Check Version:
firefox --version (Linux/macOS) or check about:firefox (all platforms)Verify Fix Applied:
Confirm Firefox version is 148 or higher in about:firefox.📡 Detection & Monitoring
Log Indicators:
- Browser crash reports with WebAssembly-related stack traces
- Unexpected memory access patterns in browser process
Network Indicators:
- Unusual WebAssembly module downloads from suspicious domains
- Multiple rapid WebAssembly compilation requests
SIEM Query:
source="firefox.log" AND ("WebAssembly" OR "wasm") AND ("crash" OR "access violation")