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High severityOSV Advisory· Published Jan 5, 2026· Updated Mar 5, 2026

MCP TypeScript SDK UriTemplate Exploded Array Pattern ReDoS

CVE-2026-0621

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.

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Affected packages

Versions sourced from the GitHub Security Advisory.

PackageAffected versionsPatched versions
@modelcontextprotocol/sdknpm
< 1.25.21.25.2

Affected products

62

Patches

Vulnerability mechanics

References

7

News mentions

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