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)
Published · last modified .
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.
EPSS exploit prediction
EPSS: 0.004 (36.2th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 36th percentile — 36.2% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.004 · newest: 0.004 · change: +0.000
Affected products
Weakness classification (CWE)
References
- github.com/modelcontextprotocol/typescript-sdk/issues/965 (issue-tracking, Exploit, Issue Tracking)
- www.vulncheck.com/advisories/mcp-typescript-sdk-uritemplate-exploded-array-patt… (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.