CVE-2025-4089
📋 TL;DR
This vulnerability in Firefox and Thunderbird's 'copy as cURL' feature allows attackers to craft malicious commands with insufficient escaping of special characters. If a user copies and executes such a command, it could lead to local code execution on their system. This affects all Firefox and Thunderbird users running versions below 138.
💻 Affected Systems
- Mozilla Firefox
- Mozilla Thunderbird
📦 What is this software?
Firefox by Mozilla
Thunderbird by Mozilla
⚠️ Risk & Real-World Impact
Worst Case
Full local code execution with user privileges, allowing attackers to install malware, steal data, or gain persistent access to the system.
Likely Case
Limited command execution in user context, potentially leading to data theft or further privilege escalation through chained attacks.
If Mitigated
No impact if users don't execute untrusted cURL commands or if proper input validation is implemented.
🎯 Exploit Status
Exploitation requires social engineering to trick users into copying and executing malicious commands. No authentication needed for initial access.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Firefox 138, Thunderbird 138
Vendor Advisory: https://www.mozilla.org/security/advisories/mfsa2025-28/
Restart Required: Yes
Instructions:
1. Open Firefox/Thunderbird. 2. Click menu → Help → About Firefox/Thunderbird. 3. Allow automatic update to version 138. 4. Restart the application when prompted.
🔧 Temporary Workarounds
Disable Developer Tools
allPrevent access to the 'copy as cURL' feature by disabling developer tools
about:config → devtools.enabled = false
User Education
allTrain users to never copy and execute cURL commands from untrusted sources
🧯 If You Can't Patch
- Implement application whitelisting to prevent execution of unauthorized commands
- Use network segmentation to limit potential lateral movement if compromised
🔍 How to Verify
Check if Vulnerable:
Check Firefox/Thunderbird version: about:support → Application Basics → Version. If below 138, vulnerable.Check Version:
Firefox: about:support | grep 'Version'; Thunderbird: about:support | grep 'Version'Verify Fix Applied:
Confirm version is 138 or higher in about:support after update.📡 Detection & Monitoring
Log Indicators:
- Unusual command execution events in system logs
- Firefox/Thunderbird crash reports with suspicious parameters
Network Indicators:
- Unexpected outbound connections following cURL command execution
- DNS queries to suspicious domains
SIEM Query:
EventID=4688 AND (CommandLine LIKE '%curl%' AND ParentImage LIKE '%firefox%' OR ParentImage LIKE '%thunderbird%')