# CVE-2026-0621: MCP TypeScript SDK UriTemplate Exploded Array Pattern ReDoS

> CVE-2026-0621: MCP TypeScript SDK UriTemplate Exploded Array Pattern ReDoS. CVSS 7.5 (CVSS 3.1).

Canonical: https://rewindex.com/cve/CVE-2026-0621
Last updated: 2026-10-08T16:16:55Z

- Published: 2026-01-05 20:57 UTC · Updated: 2026-10-08 16:16 UTC · Assigner: VulnCheck
- CVSS: 7.5 (CVSS 3.1) · Severity: High · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- EPSS: 0.44%, 38th percentile (scored 2026-10-25)
- CISA KEV: no
- CWE: CWE-1333

## Description

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.

## Affected vendors and products

- Anthropic: MCP TypeScript SDK

## Tracked companies

- [Anthropic](https://rewindex.com/company/anthropic.md)

## References

- [CVE record on cve.org](https://www.cve.org/CVERecord?id=CVE-2026-0621)
- [NVD entry](https://nvd.nist.gov/vuln/detail/CVE-2026-0621)
- [https://github.com/modelcontextprotocol/typescript-sdk/issues/965](https://github.com/modelcontextprotocol/typescript-sdk/issues/965)
- [https://www.vulncheck.com/advisories/mcp-typescript-sdk-uritemplate-exploded-array-pattern-redos](https://www.vulncheck.com/advisories/mcp-typescript-sdk-uritemplate-exploded-array-pattern-redos)

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_Sources: CVE records from the CVE Program (cve.org). CVE® is a registered trademark of The MITRE Corporation. (https://www.cve.org/) This product uses data from the NVD API but is not endorsed or certified by the NVD. (https://nvd.nist.gov/) Known Exploited Vulnerabilities catalog from CISA. (https://www.cisa.gov/known-exploited-vulnerabilities-catalog) EPSS scores from FIRST (Exploit Prediction Scoring System). (https://www.first.org/epss/)_


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Canonical: https://rewindex.com/cve/CVE-2026-0621 · Markdown: https://rewindex.com/cve/CVE-2026-0621.md · JSON: https://rewindex.com/api/v1/cves/CVE-2026-0621 · Data licensed CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/) · Generated 2026-10-26T03:09:01.606Z