HIGH

CVE-2026-21637

CVSS v3

7.5

HIGH

EPSS Score

1.1 %

exploit probability, as of 2026-09-25

CISA KEV

known exploited

Exploitation

—

SSVC status

Description

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 ca

Technical details

CVSS v3 Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H/E:U/RL:O/RC:C
Published: 2026-05-07
Last Modified: 2026-01-30
MSRC Title: HackerOne: CVE-2026-21637 TLS PSK/ALPN Callback Exceptions Bypass Error Handlers

Frequently asked questions

What is CVE-2026-21637?

Is CVE-2026-21637 actively exploited?

Active exploitation of CVE-2026-21637 has not been confirmed. Its EPSS score was 1.1% on 2026-09-25, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2026-21637?

CVE-2026-21637 has a CVSS v3 base score of 7.5 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H/E:U/RL:O/RC:C.

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