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CVE-2026-0621

MCP TypeScript SDK UriTemplate Exploded Array Pattern ReDoS

Published: Jan 5, 2026Updated: Jan 30, 2026 Sources: CVE List NVD GHSACWE-1333
NVD MITRE
7.5CVSSHIGH
EPSS Score
0.4%
Top 68.4%
CISA KEV
Not in KEV
Exploits
1 Known
Remediation
Patch Available

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.

CVSS Vector Breakdown

AV:NAC:LPR:NUI:NS:UC:NI:NA:H
Exploitability
AV:NAttack Vector
Network
AC:LAttack Complexity
Low
PR:NPrivileges Required
None
UI:NUser Interaction
None
Scope
S:UScope
Unchanged
Impact
C:NConfidentiality
None
I:NIntegrity
None
A:HAvailability
High
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Weaknesses

CWE-1333

Affected Products

mcp typescript sdklfprojects
Mixed
AI / ML / notebook-mlops
@modelcontextprotocol/sdknpmOSS Libraries
MCP TypeScript SDKAnthropic
SaaS
AI / ML / llm-serving-inference
lfprojectsoss-projectAI / MLaka mlflow, valkey, model context protocol servers, mcp servers
npmpackage-ecosystemOSS Libraries
anthropiccommercialUSAI / MLaka claude

Attack Graph

Products CVE Techniques Tactics

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Exploitability

1 exploit source identified

Exploit details including PoC links, Metasploit modules, and scanner templates are available after registration.

View exploit details
Official Patch Available

MITRE ATT&CK

1 technique
Impact
View detailed technique mapping

References

https://github.com/modelcontextprotocol/typescript-sdk/issues/965
github.com
https://www.vulncheck.com/advisories/mcp-typescript-sdk-uritemplate-exploded-array-pattern-redos
vulncheck.com
https://github.com/modelcontextprotocol/typescript-sdk/security/advisories/GHSA-cqwc-fm46-7fff
github.com
and 4 more references View all →

Timeline

Published
Jan 5, 2026
Last Updated
Jan 30, 2026

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