CVE-2025-9611 is a vulnerability classified under CWE-749 (Exposed Dangerous Method or Function) affecting Microsoft Playwright MCP Server versions prior to 0.0.40. The core issue is the failure to validate the Origin header on incoming HTTP connections to the MCP server. This validation lapse allows attackers to perform DNS rebinding attacks, a technique where a malicious website causes a victim’s browser to resolve a domain name to a local IP address (e.g., localhost). Consequently, the attacker can send unauthorized HTTP requests from the victim’s browser to the locally running MCP server, bypassing same-origin policy protections. This leads to unintended invocation of MCP tool endpoints, which may expose sensitive operations or data. The vulnerability does not require prior authentication and can be triggered by user interaction with a crafted malicious webpage. The CVSS 4.0 vector indicates a network attack vector (AV:N), low attack complexity (AC:L), no privileges required (PR:N), but requires user interaction (UI:P). The impact on confidentiality and integrity is low, but availability impact is high due to potential disruption or misuse of MCP server functions. The scope is limited to systems running vulnerable MCP server instances locally. No patches or known exploits are currently available, but the vulnerability is publicly disclosed and should be addressed promptly.

For European organizations, the impact of CVE-2025-9611 can be significant, especially for those utilizing Microsoft Playwright MCP Server in development, testing, or automation environments. Successful exploitation could allow attackers to manipulate local MCP server endpoints, potentially leading to unauthorized actions, data leakage, or service disruption. This could compromise internal testing environments or automation pipelines, affecting software quality and operational continuity. Since the attack leverages DNS rebinding via a victim’s browser, employees visiting malicious websites could inadvertently trigger the exploit, increasing the risk of insider threats or supply chain attacks. The vulnerability’s high availability impact could disrupt critical development workflows. Organizations handling sensitive or regulated data may face compliance risks if local services are compromised. The lack of authentication requirement and ease of exploitation via user interaction heighten the threat level. However, the vulnerability does not directly expose production systems unless MCP server instances are exposed or misconfigured.

To mitigate CVE-2025-9611, European organizations should implement the following specific measures: 1) Immediately upgrade Microsoft Playwright MCP Server to version 0.0.40 or later once available, as this will include proper Origin header validation. 2) Until patches are released, restrict access to the MCP server by binding it to localhost interfaces only and avoid exposing it on network interfaces accessible by untrusted users. 3) Employ network-level controls such as firewall rules or local host-based access controls to prevent unauthorized inbound connections to the MCP server ports. 4) Educate users about the risks of visiting untrusted websites to reduce the likelihood of DNS rebinding attacks via browsers. 5) Use browser security features or extensions that mitigate DNS rebinding attacks, such as disabling or restricting DNS rebinding protections. 6) Monitor local MCP server logs for unusual or unauthorized requests indicative of exploitation attempts. 7) Implement Content Security Policy (CSP) headers and other web security best practices to limit exposure to malicious web content. 8) Conduct internal audits to identify all instances of Playwright MCP Server deployment and ensure they are secured or isolated. These targeted actions go beyond generic advice by focusing on network isolation, user awareness, and proactive monitoring specific to the nature of this vulnerability.