CVE-2026-0621: Anthropic's MCP TypeScript SDK versions up to and including 1.25.1 contain a regular expression denial of service (ReDoS

Anthropic's MCP TypeScript SDK (a toolkit for building AI applications) versions up to 1.25.1 has a ReDoS vulnerability (regular expression denial of service, where a maliciously designed input causes the regex parser to work extremely hard and freeze the system) in its UriTemplate class. An attacker can send a specially crafted URI (web address) that makes the Node.js process (the JavaScript runtime environment) consume excessive CPU and stop responding, causing the application to crash or become unavailable.