What is CVE-2026-0621?

CVE-2026-0621 is a high-severity vulnerability in Anthropic Mcp Typescript Sdk, classified under Inefficient Regular Expression Complexity. CVSS score: 7.5/10. Published 2026-01-05.

How severe is CVE-2026-0621?

High severity. CVSS v3 base score is 7.5 out of 10.

Vulnerability in Anthropic Mcp Typescript Sdk

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.

Vulnerability class: ReDoS (Regular Expression Denial of Service)

EPSS: 0.004 (32.7th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

Affected products

Anthropic Mcp Typescript Sdk — versions 0
Lfprojects Mcp_typescript_sdk

Weakness classification (CWE)

CWE-1333 — Inefficient Regular Expression Complexity

References

disclosure@vulncheck.com (issue-tracking, Exploit, Issue Tracking)
disclosure@vulncheck.com (Third Party Advisory, third-party-advisory)

Frequently asked questions

What is CVE-2026-0621?: CVE-2026-0621 is a high-severity vulnerability in Anthropic Mcp Typescript Sdk, classified under Inefficient Regular Expression Complexity. CVSS score: 7.5/10. Published 2026-01-05.
How severe is CVE-2026-0621?: High severity. CVSS v3 base score is 7.5 out of 10.