Malicious MCP Server Uncovered in 'postmark-mcp' npm Package Supply Chain Breach
In September 2025, cybersecurity researchers identified the first active malicious deployment of a Model Context Protocol (MCP) server, delivered through a compromised open-source npm package called "postmark-mcp." The attacker, masquerading as a legitimate developer, introduced rogue code into the package to stealthily exfiltrate user emails to an adversary-controlled MCP server. The package closely mimicked the official Postmark Labs library, making detection challenging for organizations relying on the trusted supply chain. The incident highlights the growing sophistication and operational impact of supply chain compromise, especially within widely used repositories like npm. This supply chain breach underscores a wider trend of attackers targeting open-source ecosystems to weaponize trusted libraries for data theft and persistent access, driving regulatory scrutiny and risk to software providers and their customers. With the acceleration of software supply chain attacks, organizations face increased pressure to enhance dependency audits and adopt zero trust controls.
Kill Chain