Vulnerability Report

CVE-2026-0621

Title: Regular expression denial of service (ReDoS) in Anthropic's MCP TypeScript SDK

DoS

Proof Of Concept

No public PoC currently indexed for CVE-2026-0621.

CWE Category CWE-1333

Published Date Jan 05, 2026

Modified Date Jan 30, 2026

Exploit Status Not Found

Score 8.7 CVSS v4.0

Exploit Probability (EPSS)

0.40%

Vulnerability Summary

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.

Impacted Vendors

lfprojects 1

Reference Links

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

CVSS v4.0

Source Entity [email protected]

Severity HIGH

8.7

Attack Vector

NETWORK

Complexity

LOW

Privileges

N/A

Interaction

NONE

Confidentiality

N/A

Integrity

N/A

Availability

N/A

Scope

N/A

RAW VECTOR

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

CVSS v3.1