HighVulnerability

CVE-2026-0621: Anthropic MCP TypeScript SDK ReDoS in UriTemplate array pattern matching

Source: NVD(opens in a new tab)
Identifier: CVE-2026-0621
Published: January 5, 2026
Record updated: October 9, 2026

Affected: @modelcontextprotocol/sdk >= 1.3.0, < 1.25.2
Fixed in: 1.25.2
released January 7, 2026, 1 day after disclosure
Known exploitation: Not listed in the CISA Known Exploited Vulnerabilities catalog at the last check.
EPSS: 0.4%

Summary

Anthropic's MCP TypeScript SDK, versions up to and including 1.25.1, contains a regular expression denial of service (ReDoS) flaw (CVE-2026-0621) in the UriTemplate class when it processes RFC 6570 exploded array patterns. The dynamically generated regular expression contains nested quantifiers that can cause catastrophic backtracking on crafted input, driving CPU use up. An attacker who supplies a malicious URI can make the Node.js process unresponsive.

Mitigation

The source does not state a fix yet. Check the original advisory for updates.

Details

Scores and exploitation

CVSS score: 7.5(high)
Patch available: Yes
EPSS: 0.4%Estimated probability that this CVE is exploited in the next 30 days, from the FIRST Exploit Prediction Scoring System. Read on November 4, 2026.

Weaknesses and techniques

Weakness (CWE): CWE-1333

Affected

Packages: @modelcontextprotocol/sdk@>= 1.3.0, < 1.25.2 (fixed: 1.25.2)
Vendors: Anthropic

Classification

Attack type: Denial of service
Attack sophistication: Trivial
AI component targeted: API
Impact: Availability
Labels: security

How this record was produced

Summaries, mitigations and labels on this page are generated automatically from the source. The linked source is authoritative. The source gives this advisory a description and no title, so the title above is a headline generated from the source text.

Original source: https://nvd.nist.gov/vuln/detail/CVE-2026-0621

First tracked: February 15, 2026 at 08:50 PM ET, from NVD/CVE Database

Classifier: claude-haiku-5-5, prompt v4

Classifier confidence: 90% (self-assessed)

Affected packages in the Exposure Registry

Matched by package name and ecosystem. Each entry shows whether the package delegates to a language model and how many tracked packages depend on it.

@modelcontextprotocol/sdknpmLLM dependency since 2024-11-11 · 19 tracked dependents

Topics

Model Context Protocol

Summary

Mitigation

Affected packages in the Exposure Registry

Topics

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