Security researchers have flagged a serious vulnerability in a diagnostic tool built by Anthropic, which could put AI developers at risk. The flaw discovered in the MCP Inspector utility may allow external attackers to gain full control of a developer’s system without requiring physical access.
The issue, tracked as CVE-2025-49596 and rated 9.4 on the CVSS scale, was disclosed by Oligo Security. Researchers say this marks one of the first major remote code execution (RCE) vulnerabilities targeting Anthropic’s Model Context Protocol (MCP) ecosystem.
The danger lies in how the MCP Inspector is typically deployed. Setting up the tool using the official guidelines often leaves it exposed, as it starts running without essential safeguards like login verification or data encryption. This misstep creates an opportunity for attackers to abuse the system from afar.
The attack chain leverages a long-standing flaw in modern browsers, dubbed “0.0.0.0 Day,” combined with a cross-site request forgery (CSRF) bug in the MCP Inspector. Together, these vulnerabilities make it possible for a user simply visiting a booby-trapped website to trigger remote code execution on their own system.
“This vulnerability creates a huge attack surface. Developers might unknowingly be running a server that accepts unauthenticated commands from public websites,” said Avi Lumelsky, a researcher at Oligo Security. “Attackers could install backdoors, steal data, or move laterally across networks.”
The core of the issue is how browsers mishandle requests to the IP address 0.0.0.0, often treating it as localhost. The MCP Inspector, by default, listens on this address, meaning that anyone who can lure a developer into clicking a link or loading a webpage could run terminal commands on their machine.
Oligo’s proof-of-concept demonstrates how easily this can be exploited. Attackers can slip malicious JavaScript into a webpage that, once visited, silently sends instructions to the MCP Inspector’s server, triggering actions like file creation or script execution without the user ever knowing.
In some cases, DNS rebinding techniques can also be used to bypass restrictions and reach internal services, even on machines configured to accept only local traffic.
Anthropic acknowledged the issue and released a fix on June 13, 2025, with version 0.14.1 of the MCP Inspector. The update adds mandatory session tokens, verifies HTTP origin headers, and blocks unauthorized access by default. These changes significantly strengthen the tool’s defenses against browser-based threats.
“We appreciate Anthropic’s rapid response,” Oligo noted. The security team implemented robust safeguards that now prevent CSRF and rebinding attacks from web pages, marking a much-needed improvement.
Despite the fix, researchers warn that many open-source projects and enterprise environments are likely still running outdated versions, especially since the MCP Inspector often installs as a dependency inside local node_modules folders.
Security professionals urge developers using the MCP tooling to check their installed version immediately. A simple terminal command (npm list -g) can help determine if the vulnerable build is still active. If so, users are advised to upgrade to vers0.14.1 or later.
MCP, the framework designed to connect large language models with outside tools and data sources, has quickly gained traction among AI developers. Built with support for Python and JavaScript, it’s now widely used across the industry. But as more teams bring it into real-world environments, default security gaps are becoming a growing concern.
While MCP’s open nature fosters rapid innovation, it also places the burden of security on end users. Until the ecosystem matures, experts say caution and configuration mindfulness are crucial.
“This episode highlights how browser quirks and developer tools can collide in dangerous ways,” said Lumelsky. “Even something as benign as visiting a tech blog could turn into a full system compromise if you’re running a misconfigured server in the background.”
