TI-2026-00421 Aliases CVE-2026-0621 GHSA-8r9q-7v3j-jr4g

MCP TypeScript SDK UriTemplate Exploded Array Pattern ReDoS

HIGH 77CWE-1333Published 2026-01-05 · Updated 2026-10-08

Key facts

Attack vector: Network
Privileges required: None
User interaction: None
Attack complexity: Low
Attack requirements: None
Impact type: Denial of service
Confidentiality · integrity · availability: None · None · High
Fix status: Fixed

Attack profile from CVSS 4.0 · CNA. Fix status from CNA and GitHub. Impact type from CWE-1333.

Summary

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.

Why it matters now

Exploitation Proof of concept CISA SSVC · not in CISA KEV

EPSS 0.00438 38th percentileScored 2026-11-07

Public exploit Yes 1 exploit referenceTagged by NVD

Fix Fixed @modelcontextprotocol/sdk (npm): 1.25.2

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation: Poc
Automatable: Yes
Technical impact: Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

Vendor	Product	Affected versions	Fixed in	Status	Source
anthropics	MCP TypeScript SDK	up to 1.25.1	—	No fix listed	CNA
—	@modelcontextprotocol/sdk (npm)	1.3.0 to before 1.25.2	1.25.2	Patch available	GHSA-8r9q-7v3j-jr4g

MCP TypeScript SDK Vendoranthropics Affected up to 1.25.1 Fixed in — No fix listed CNA
@modelcontextprotocol/sdk (npm) Vendor— Affected 1.3.0 to before 1.25.2 Fixed in 1.25.2 Patch available GHSA-8r9q-7v3j-jr4g

CPE configurations NVD · 1

CPE	Versions	Role	Vendor
cpe:2.3:a:lfprojects:mcp_typescript_sdk::::::::	up to 1.25.1	Vulnerable	MLflow

cpe:2.3:a:lfprojects:mcp_typescript_sdk:*:*:*:*:*:*:*:* Versions up to 1.25.1 Vulnerable ·MLflow

Remediation

Fix · GHSA-8r9q-7v3j-jr4g @modelcontextprotocol/sdk (npm) Fixed in 1.25.2 Advisory →

Timeline

2026-10-02 Threatist record created from CVE-2026-0621
2026-10-03 Alias added: GHSA-8r9q-7v3j-jr4g

References

Exploit 1

https://github.com/modelcontextprotocol/typescript-sdk/issues/965

Advisory 1

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

Other 5

TI-2026-79288 Out-of-bounds write in Google Brotli decoder KEVCVSS 4.0CRITICAL 9.2
TI-2025-40558 Claude Code Command Validation Bypass Allows Arbitrary Code Execution CVSS 4.0HIGH 8.7
TI-2025-36683 Claude Code vulnerable to arbitrary code execution caused by maliciously configured git email CVSS 4.0HIGH 8.7
TI-2025-24240 Anthropic Slack MCP Server Data Exfiltration via Link Unfurling CVSS 4.0CRITICAL 9.3
TI-2025-32918 Claude Code IDE extensions allow websocket connections from arbitrary origins CVSS 4.0HIGH 8.8
TI-2025-37066 Claude Code's startup trust dialog could lead to Command Execution attack CVSS 4.0HIGH 8.7

See all 46 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences