CVE-2025-9611 is a vulnerability identified in Microsoft Playwright MCP Server versions before 0.0.40, where the server fails to validate the Origin header on incoming HTTP connections. This security oversight allows an attacker to conduct DNS rebinding attacks by luring a victim into visiting a malicious website. DNS rebinding manipulates the victim's browser to bypass same-origin policies, enabling the attacker to send unauthorized requests to the locally running MCP server. The MCP server exposes various tool endpoints that, when invoked without proper authorization, can lead to unintended actions or data exposure. The vulnerability is categorized under CWE-749, indicating the exposure of dangerous methods or functions due to insufficient access control. The attack vector is network-based, requiring no privileges or authentication but does require user interaction (visiting a malicious site). The CVSS 4.0 score of 7.2 highlights the high severity, with partial impacts on confidentiality, integrity, and availability. No patches or exploits are currently documented, but the vulnerability's nature suggests it could be exploited to manipulate local services or extract sensitive information. The failure to validate the Origin header is a critical design flaw that undermines the security boundary between the browser and local server components.

For European organizations, this vulnerability poses a significant risk especially to development teams and environments using Microsoft Playwright MCP Server. Exploitation could lead to unauthorized local service access, potentially exposing sensitive internal tools or data. This could result in data leakage, unauthorized command execution, or disruption of local development workflows. Since Playwright is widely used for automated testing and browser interaction, compromised MCP servers could undermine software integrity and trust in CI/CD pipelines. The attack requires user interaction, so phishing or social engineering campaigns could be leveraged to trigger exploitation. Organizations with remote or hybrid workforces may face increased risk due to varied endpoint security postures. The partial impact on confidentiality, integrity, and availability means attackers could both steal data and disrupt operations. Given the lack of known exploits, the threat is currently theoretical but should be treated proactively to prevent future incidents.

1. Upgrade Microsoft Playwright MCP Server to version 0.0.40 or later where the Origin header validation issue is fixed. 2. Implement network segmentation and firewall rules to restrict access to the MCP server from untrusted networks or browsers. 3. Use browser security policies such as Content Security Policy (CSP) and SameSite cookies to reduce the risk of DNS rebinding attacks. 4. Educate users about the risks of visiting untrusted websites and phishing attempts that could trigger exploitation. 5. Monitor local MCP server logs for unusual or unauthorized requests that may indicate attempted exploitation. 6. Employ endpoint protection solutions that can detect suspicious browser behaviors or network anomalies. 7. Consider disabling or restricting MCP server endpoints that are not essential to reduce the attack surface. 8. Conduct regular security assessments of development environments to identify and remediate similar origin validation issues.