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Vulnerabilities

Vulnerability · 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

Published Jan 5, 2026 · catalog updated Oct 26, 2026 · Anthropic MCP TypeScript SDK

Last checked Oct 29, 2026. A connected source was read within the last 7 days.

Check if you run it

No confirmed exploitation is on record for CVE-2026-0621. EPSS is 0.44%. Act only if a listed version of Anthropic MCP TypeScript SDK is installed.

Gaps on this record

  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
Severity
High8.7
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.44%
Remediation
Version ranges on file
Affected products
cpe lfprojects/mcp typescript sdk · vendor Anthropic MCP TypeScript SDK 0 ≤1.25.1

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.

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • cpe lfprojects/mcp typescript sdk<= 1.25.1
  • vendor Anthropic MCP TypeScript SDK 0 ≤1.25.10 ≤1.25.1

How to fix CVE-2026-0621

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-0621. EPSS is 0.44%. Act only if a listed version of Anthropic MCP TypeScript SDK is installed.

Which versions are affected?

Compare what you have installed with lfprojects/mcp typescript sdk <= 1.25.1; Anthropic MCP TypeScript SDK 0 ≤1.25.1 0 ≤1.25.1. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

CWE-1333: Inefficient Regular Expression Complexity. EPSS 0.44%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

No public source repository is identified for this product.

Timeline

Detection, updates, and resolution for this record.

  1. Jan 5, 2026 · NIST NVD

    Detected

    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 excess

  2. Oct 26, 2026 · NIST NVD

    Updated

    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 excess

Sources

  • CVE.orgVulnerability recordCVE-2026-0621

    Official CVE identifier

    cve.org
  • EUVDVulnerability recordEUVD-2026-0800

    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

    euvd.enisa.europa.eu
  • NIST NVDVulnerability recordCVE-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

    nvd.nist.gov

References

Freshness

Last verified in this catalog Oct 29, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.

  • EUVDOct 28, 2026
  • CVE.orgOct 27, 2026
  • NIST NVDOct 27, 2026