How severe is CVE-2026-21637?

CVE-2026-21637 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-2026-21637 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (60th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-21637?

CVE-2026-21637 affects Nodejs Node.js. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-21637?

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-2026-21637 have an EU (EUVD) identifier?

Yes. CVE-2026-21637 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-3327.

When was CVE-2026-21637 published?

CVE-2026-21637 was published on 2026-01-20 and last updated on 2026-06-17.

CVE-2026-21637

CVE-2026-21637 is a high-severity vulnerability in Nodejs Node.js 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-400.

Key facts

Severity: High (CVSS 3.x base score 7.5)
EPSS exploit prediction: 1% (60th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-3327
Weakness: CWE-400
Affected product: Nodejs Node.js
Published: 2026-01-20
Last modified: 2026-06-17

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 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.

Frequently asked questions

What is CVE-2026-21637?: 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.
How severe is CVE-2026-21637?: CVE-2026-21637 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-2026-21637 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (60th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-21637?: CVE-2026-21637 affects Nodejs Node.js. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-21637?: 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-2026-21637 have an EU (EUVD) identifier?: Yes. CVE-2026-21637 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-3327.
When was CVE-2026-21637 published?: CVE-2026-21637 was published on 2026-01-20 and last updated on 2026-06-17.

References

https://nodejs.org/en/blog/vulnerability/december-2025-security-releases

Affected products (1)

cpe:2.3:a:nodejs:node.js:*:*:*:*:-:*:*:*

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