CVE-2025-9866
📋 TL;DR
This vulnerability allows attackers to bypass Chrome's Content Security Policy (CSP) through malicious extensions, enabling injection of unauthorized scripts or content. It affects all users running vulnerable versions of Google Chrome and Chromium-based browsers. Attackers can exploit this via crafted HTML pages to execute arbitrary code in the browser context.
💻 Affected Systems
- Google Chrome
- Chromium-based browsers
📦 What is this software?
Chrome by Google
Google Chrome is the world's most popular web browser, used by over 3 billion users globally across Windows, macOS, Linux, Android, and iOS platforms. As a Chromium-based browser developed by Google, Chrome dominates the browser market with approximately 65% market share, making it a critical compon...
Learn more about Chrome →⚠️ Risk & Real-World Impact
Worst Case
Complete compromise of browser session allowing data theft, credential harvesting, and installation of persistent malware through script injection.
Likely Case
Cross-site scripting attacks, session hijacking, and unauthorized data exfiltration from vulnerable websites.
If Mitigated
Limited impact with proper network segmentation and browser sandboxing, though CSP bypass remains possible.
🎯 Exploit Status
Exploitation requires user interaction (visiting malicious page) but no authentication. Technical details are limited in public disclosure.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 140.0.7339.80 and later
Vendor Advisory: https://chromereleases.googleblog.com/2025/09/stable-channel-update-for-desktop.html
Restart Required: Yes
Instructions:
1. Open Chrome settings. 2. Click 'About Chrome'. 3. Allow Chrome to check for and install updates. 4. Restart Chrome when prompted.
🔧 Temporary Workarounds
Disable Extensions
allTemporarily disable all browser extensions to prevent exploitation through malicious extensions
chrome://extensions/ → Toggle off all extensions
Enable Enhanced CSP
allImplement stricter Content Security Policy headers on web servers
Content-Security-Policy: default-src 'self'; script-src 'self'
🧯 If You Can't Patch
- Use alternative browsers until patch can be applied
- Implement network filtering to block known malicious domains and script sources
🔍 How to Verify
Check if Vulnerable:
Check Chrome version in settings → About Chrome. If version is below 140.0.7339.80, system is vulnerable.Check Version:
google-chrome --version (Linux) or chrome://version/ in browserVerify Fix Applied:
Confirm Chrome version is 140.0.7339.80 or higher in About Chrome page.📡 Detection & Monitoring
Log Indicators:
- Unusual extension activity
- CSP violation reports in server logs
- Multiple script load failures
Network Indicators:
- Unexpected external script loads
- CSP bypass attempts in HTTP headers
SIEM Query:
source="chrome" AND (event="csp_violation" OR event="extension_install")