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CVE-2025-9866: Google Chrome Extensions Content Security Policy Bypass Vulnerability

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Overview

CVE-2025-9866 is a significant cybersecurity vulnerability that affects the Google Chrome browser, particularly in its handling of Extensions. The vulnerability results from an inappropriate implementation in Extensions in versions of Google Chrome prior to 140.0.7339.80. Consequently, this flaw allows a remote attacker to bypass the content security policy through a meticulously crafted HTML page. Given the widespread use of Google Chrome, this vulnerability underscores the critical nature of maintaining up-to-date browser versions and ensuring adherence to best cybersecurity practices.

Vulnerability Summary

CVE ID: CVE-2025-9866
Severity: Medium (CVSS: 8.8)
Attack Vector: Network
Privileges Required: None
User Interaction: Required
Impact: Potential system compromise or data leakage

Affected Products

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Product | Affected Versions

Google Chrome | Prior to 140.0.7339.80

How the Exploit Works

The exploit leverages an inappropriate implementation in Google Chrome’s Extensions feature. An attacker crafts a specific HTML page designed to bypass the content security policy of the browser. Once a user interacts with this page through their vulnerable Google Chrome version, the attacker can potentially gain unauthorized access to the system or sensitive data.

Conceptual Example Code

The following conceptual example illustrates how an HTTP request might look when exploiting this specific vulnerability:

GET /malicious.html HTTP/1.1
Host: attacker.example.com
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/70.0.3538.77 Safari/537.36

The `malicious.html` page would contain the exploit code designed to bypass the content security policy of Google Chrome. Upon successful execution, this could lead to unauthorized system access or data leakage.

Mitigation and Prevention

The ideal mitigation for CVE-2025-9866 is to apply the vendor-supplied patch, which in this case is to update Google Chrome to version 140.0.7339.80 or later. This update fixes the inappropriate implementation and prevents the possibility of content security policy bypass.
However, in situations where immediate application of the vendor patch is not feasible, a Web Application Firewall (WAF) or Intrusion Detection System (IDS) can be used as a temporary mitigation measure. These tools can help detect and block potential exploit attempts. It’s worth noting, however, that these are stop-gap measures and don’t replace the need for applying the vendor-supplied patch.

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Disclaimer:

The information and code presented in this article are provided for educational and defensive cybersecurity purposes only. Any conceptual or pseudocode examples are simplified representations intended to raise awareness and promote secure development and system configuration practices.

Do not use this information to attempt unauthorized access or exploit vulnerabilities on systems that you do not own or have explicit permission to test.

Ameeba and its authors do not endorse or condone malicious behavior and are not responsible for misuse of the content. Always follow ethical hacking guidelines, responsible disclosure practices, and local laws.

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