CVE-2025-8037
📋 TL;DR
This vulnerability allows an attacker to set a nameless cookie with an equals sign in its value, which can shadow other cookies including those with the Secure attribute, even when set over HTTP. This affects Firefox, Firefox ESR, and Thunderbird users running vulnerable versions, potentially leading to session hijacking or authentication bypass.
💻 Affected Systems
- Firefox
- Firefox ESR
- Thunderbird
📦 What is this software?
Firefox by Mozilla
Firefox by Mozilla
Thunderbird by Mozilla
Thunderbird by Mozilla
⚠️ Risk & Real-World Impact
Worst Case
Complete session hijacking where an attacker steals authenticated sessions, accesses sensitive user data, or performs actions as the victim user.
Likely Case
Session fixation or authentication bypass allowing attackers to access user accounts with limited privileges.
If Mitigated
Minimal impact if users only visit trusted sites and have updated browsers, though cookie manipulation could still occur on compromised sites.
🎯 Exploit Status
Exploitation requires user interaction (visiting a malicious site) but no authentication to the vulnerable browser.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Firefox 141+, Firefox ESR 140.1+, Thunderbird 141+, Thunderbird 140.1+
Vendor Advisory: https://www.mozilla.org/security/advisories/mfsa2025-56/
Restart Required: Yes
Instructions:
1. Open browser settings. 2. Navigate to 'About Firefox/Thunderbird'. 3. Allow automatic update or manually download latest version from mozilla.org. 4. Restart browser after update.
🔧 Temporary Workarounds
Disable third-party cookies
allPrevents malicious sites from setting cookies that could shadow legitimate ones.
In Firefox: about:preferences#privacy > Enhanced Tracking Protection > Custom > uncheck 'Cookies'
🧯 If You Can't Patch
- Use alternative browsers (Chrome, Safari) until patches can be applied.
- Implement network filtering to block access to known malicious sites that may exploit this vulnerability.
🔍 How to Verify
Check if Vulnerable:
Check browser version in settings: Firefox/Thunderbird > Help > About Firefox/Thunderbird.Check Version:
firefox --version or thunderbird --versionVerify Fix Applied:
Confirm version is Firefox 141+, Firefox ESR 140.1+, Thunderbird 141+, or Thunderbird 140.1+.📡 Detection & Monitoring
Log Indicators:
- Unusual cookie manipulation patterns in web server logs
- Multiple cookie headers with equals signs in values
Network Indicators:
- HTTP requests with malformed cookie headers containing nameless cookies
SIEM Query:
source="web_server" AND (cookie="=" OR cookie="=value")