A critical security flaw has been identified in the open-source mcp-remote project, potentially allowing attackers to execute arbitrary operating system commands on affected machines. This vulnerability, designated as CVE-2025-6514, has been assigned a CVSS score of 9.6 out of 10, indicating its severe impact.
Understanding mcp-remote and Its Functionality
mcp-remote is a tool developed to facilitate communication between large language model (LLM) applications and remote Model Context Protocol (MCP) servers. By acting as a local proxy, mcp-remote enables LLM clients, such as Claude Desktop, to interact with MCP servers hosted externally, rather than running them locally. This setup allows for more flexible and scalable AI deployments.
Details of the Vulnerability
The vulnerability affects mcp-remote versions from 0.0.5 to 0.1.15. It arises when mcp-remote connects to an untrusted or compromised MCP server. In such scenarios, a malicious server can inject commands during the initial communication and authorization phase. When processed by mcp-remote, these commands can be executed on the host operating system, leading to potential full system compromise.
Technical Mechanism of the Exploit
The exploit leverages the OAuth authorization flow within mcp-remote. During this process, mcp-remote requests authorization server metadata from the MCP server. A malicious server can respond with a crafted `authorization_endpoint` value that exploits the behavior of the `open` npm package used by mcp-remote. On Windows systems, this can lead to the execution of arbitrary commands through PowerShell’s subexpression evaluation feature. For instance, a malicious server might return an `authorization_endpoint` like `a:$(cmd.exe /c whoami > c:\temp\pwned.txt)`, causing the command to be executed on the client machine.
Potential Impact
The implications of this vulnerability are significant:
– Remote Code Execution (RCE): Attackers can execute arbitrary commands on the affected system, potentially leading to data theft, installation of malware, or further network infiltration.
– System Compromise: By exploiting this flaw, attackers can gain full control over the compromised machine, allowing them to manipulate files, install backdoors, or disrupt services.
– Widespread Exposure: With over 437,000 downloads of mcp-remote to date, a substantial number of systems are potentially at risk if they are running vulnerable versions and connecting to untrusted MCP servers.
Mitigation Strategies
To protect systems from this vulnerability, the following steps are recommended:
1. Update mcp-remote: Users should upgrade to version 0.1.16 or later, which addresses this security flaw.
2. Connect to Trusted MCP Servers: Ensure that mcp-remote only connects to known and trusted MCP servers to prevent malicious interactions.
3. Use Secure Connections: Always establish connections over HTTPS to safeguard against man-in-the-middle attacks and ensure data integrity.
4. Audit Configurations: Regularly review and audit MCP configurations to identify and rectify any insecure settings or connections.
Broader Implications in the MCP Ecosystem
This discovery follows another critical vulnerability (CVE-2025-49596) found in the MCP Inspector tool, which also allowed for remote code execution. These incidents highlight the importance of rigorous security practices within the MCP ecosystem. As MCP tools become more integrated into AI development workflows, ensuring their security is paramount to prevent potential exploits that could compromise entire systems.
Conclusion
The identification of CVE-2025-6514 in mcp-remote underscores the critical need for vigilance in the deployment and maintenance of AI development tools. By promptly updating to the latest versions, connecting only to trusted servers, and adhering to secure connection protocols, users can mitigate the risks associated with this vulnerability. As the MCP ecosystem continues to evolve, ongoing security assessments and proactive measures will be essential in safeguarding against emerging threats.
