CVE-2026-0890
📋 TL;DR
This CVE describes a spoofing vulnerability in Firefox and Thunderbird's DOM copy-paste and drag-drop components. Attackers can manipulate clipboard or drag-drop operations to trick users into interacting with malicious content. It affects Firefox versions below 147, Firefox ESR below 140.7, Thunderbird below 147, and Thunderbird ESR below 140.7.
💻 Affected Systems
- Firefox
- Firefox ESR
- Thunderbird
- Thunderbird ESR
📦 What is this software?
Firefox by Mozilla
Firefox by Mozilla
Thunderbird by Mozilla
Thunderbird by Mozilla
⚠️ Risk & Real-World Impact
Worst Case
An attacker could spoof legitimate UI elements during copy-paste or drag-drop operations, potentially tricking users into pasting malicious content or performing unintended actions that could lead to credential theft or system compromise.
Likely Case
Most probable impact is UI spoofing where users are tricked into copying/pasting or dragging/dropping malicious content, potentially leading to phishing attacks or unintended data exposure.
If Mitigated
With proper controls like updated browsers and user awareness training, impact is limited to minor UI confusion with minimal security consequences.
🎯 Exploit Status
Exploitation requires user interaction (copy-paste or drag-drop actions) but no authentication. The CWE-290 (Authentication Bypass by Spoofing) suggests this could be used to bypass security controls.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Firefox 147+, Firefox ESR 140.7+, Thunderbird 147+, Thunderbird ESR 140.7+
Vendor Advisory: https://www.mozilla.org/security/advisories/mfsa2026-01/
Restart Required: Yes
Instructions:
1. Open Firefox/Thunderbird. 2. Click menu → Help → About Firefox/Thunderbird. 3. Browser will check for updates and prompt to install. 4. Restart browser after update completes.
🔧 Temporary Workarounds
Disable JavaScript for untrusted sites
allPrevents malicious scripts from exploiting the DOM manipulation vulnerability
In Firefox: about:config → javascript.enabled = false
Use NoScript extension
allBlocks JavaScript execution on untrusted sites
Install NoScript extension from addons.mozilla.org
🧯 If You Can't Patch
- Implement network segmentation to restrict browser access to sensitive systems
- Deploy user awareness training about copy-paste/drag-drop security risks
🔍 How to Verify
Check if Vulnerable:
Check browser version in About dialog (menu → Help → About Firefox/Thunderbird)Check Version:
firefox --version or thunderbird --versionVerify Fix Applied:
Verify version is Firefox 147+ or Firefox ESR 140.7+ or Thunderbird 147+ or Thunderbird ESR 140.7+📡 Detection & Monitoring
Log Indicators:
- Unusual copy-paste or drag-drop events in browser logs
- Multiple failed authentication attempts following UI interactions
Network Indicators:
- Suspicious JavaScript loading patterns
- Unexpected clipboard-related network traffic
SIEM Query:
source="browser_logs" AND (event="clipboard_access" OR event="drag_drop") AND user_interaction=true