CVE-2026-21637: Node.js

High severity, CVSS 7.5. EPSS: 1.1% chance of exploitation in the next 30 days.

A flaw in Node.js TLS error handling allows remote attackers to crash or exhaust resources of a TLS server when `pskCallback` or `ALPNCallback` are in use. Synchronous exceptions thrown during these callbacks bypass standard TLS error handling paths (tlsClientError and error), causing either immediate process termination or silent file descriptor leaks that eventually lead to denial of service. Because these callbacks process attacker-controlled input during the TLS handshake, a remote client can repeatedly trigger the issue. This vulnerability affects TLS servers using PSK or ALPN callbacks across Node.js versions where these callbacks throw without being safely wrapped.

Affected products

• Node.js Node.js: from 4.0.0, before 20.20.0 (fixed in 20.20.0); from 22.0.0, before 22.22.0 (fixed in 22.22.0); from 24.0.0, before 24.13.0 (fixed in 24.13.0); from 25.0.0, before 25.3.0 (fixed in 25.3.0)

Published 2026-01-20. Last modified 2026-06-17.