What’s Vulnerable › Vulnerabilities

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

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2026-01-05 · updated 2026-10-26
• Weakness: 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 products

• modelcontextprotocol typescript-sdk: through 1.25.1

References

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

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