CVE-2026-0621

Anthropic's MCP TypeScript SDK versions up to and including 1.25.1 contain a regular expression denial of service (ReDoS) vulnerability in the UriTemplate class when processing RFC 6570 exploded array patterns. The dynamically generated regular expression used during URI matching contains nested quantifiers that can trigger catastrophic backtracking on specially crafted inputs, resulting in excessive CPU consumption. An attacker can exploit this by supplying a malicious URI that causes the Node.js process to become unresponsive, leading to a denial of service.

Score

CVSS 4.0 8.7 High

Status

Analyzed - disclosure@vulncheck.com

Published

2026-01-05

Last modified

2026-10-26

Weaknesses

CWE-1333

Affected products

• Mcp Typescript Sdk (Lfprojects)

References

• https://github.com/modelcontextprotocol/typescript-sdk/issues/965
• https://www.vulncheck.com/advisories/mcp-typescript-sdk-uritemplate-exploded-array-pattern-redos