How severe is CVE-2026-0621?

CVE-2026-0621 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2026-0621 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (32nd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-0621?

CVE-2026-0621 affects Lfprojects Mcp Typescript Sdk. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-0621?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

Does CVE-2026-0621 have an EU (EUVD) identifier?

Yes. CVE-2026-0621 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-0800.

When was CVE-2026-0621 published?

CVE-2026-0621 was published on 2026-01-05 and last updated on 2026-06-17.

CVE-2026-0621

CVE-2026-0621 is a high-severity vulnerability in Lfprojects Mcp Typescript Sdk with a CVSS 3.x base score of 7.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-1333.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v4: 8.7
EPSS exploit prediction: 0% (32nd percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-0800
Weakness: CWE-1333
Affected product: Lfprojects Mcp Typescript Sdk
Published: 2026-01-05
Last modified: 2026-06-17

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.

Frequently asked questions

What is 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.
How severe is CVE-2026-0621?: CVE-2026-0621 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2026-0621 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (32nd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-0621?: CVE-2026-0621 affects Lfprojects Mcp Typescript Sdk. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-0621?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
Does CVE-2026-0621 have an EU (EUVD) identifier?: Yes. CVE-2026-0621 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-0800.
When was CVE-2026-0621 published?: CVE-2026-0621 was published on 2026-01-05 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:lfprojects:mcp_typescript_sdk:*:*:*:*:*:*:*:*

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