CVE-2026-0621
DoS via ReDoS in Anthropic MCP TS SDK <=1.25.1 during URI matching.
Is CVE-2026-0621 being exploited?
Not confirmed. CVE-2026-0621 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 0.45% probability of exploitation in the next 30 days.
How severe is CVE-2026-0621?
CVE-2026-0621 is rated High with a CVSS score of 8.7. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2026-0621?
Not known from our data. No patch reference has been recorded for CVE-2026-0621, which is not the same as no patch existing — a fix may have shipped without a tagged reference, or after this record was written. The vendor advisory is the only authority on whether a fix exists, and mitigations may be available regardless.
What does CVE-2026-0621 affect?
CVE-2026-0621 affects Anthropic MCP TypeScript SDK <=1.25.1. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-0621?
Monitor for fixes; upgrade when patch released.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Crafted URI triggers catastrophic backtracking in UriTemplate; high CPU usage, Node.js becomes unresponsive.
Monitor only
- affected<= 1.25.1
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.