CVE-2026-0621: Anthropic's MCP TypeScript SDK versions up to and including 1.25.1 contain a regular expression denial of serv

Q: How do I fix CVE-2026-0621?

mcp typescript sdk: upgrade to newer than 1.25.1. Exact commands for each OS are on this page.

Q: Is CVE-2026-0621 being exploited?

CVE-2026-0621 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-0621 affect?

CVE-2026-0621 affects mcp typescript sdk. Severity is high (CVSS 7.5). 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 reg

Q: How urgent is CVE-2026-0621?

Priority 46/100. High severity; Public exploit reference; Remotely exploitable, no login, no user action

This week

HIGH 7.5REMOTEUPGRADE

CVE-2026-0621 is a high-severity flaw (CVSS 7.5) affecting mcp typescript sdk. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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

Why this priority

High severity
Public exploit reference
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.4% (top 62%)
CISA exploited list	No
Weakness	CWE-1333
Published	2026-01-05
Last modified	2026-10-26

Publisher (CNA): VulnCheck · Vendor: lfprojects

Last updated 2026-10-26 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-01-05 21:16 UTCPublished CVE record published
2026-10-26 21:10 UTCUpdated Record last modified

lfprojects mcp typescript sdk UPGRADE

Affected: <= 1.25.1

Fixed in: newer than 1.25.1

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy mcp-typescript-sdk || rpm -q mcp-typescript-sdk || mcp-typescript-sdk --version

2. UPGRADE to newer than 1.25.1 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade mcp-typescript-sdk

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade mcp-typescript-sdk

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-0621?

mcp typescript sdk: upgrade to newer than 1.25.1. Exact commands for each OS are on this page.

Is CVE-2026-0621 being exploited?

CVE-2026-0621 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-0621 affect?

CVE-2026-0621 affects mcp typescript sdk. Severity is high (CVSS 7.5). 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 reg

How urgent is CVE-2026-0621?

Priority 46/100. High severity; Public exploit reference; Remotely exploitable, no login, no user action

References

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