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.

Published: 2026-01-20 Last update: 2026-01-30 Assigner: [email protected] Source: [email protected]
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-21637 is rated Low Risk (36.2/100): CVSS High severity, with low exploitation likelihood (EPSS 0.06%). Monitor for updates and reassess as exploit intelligence or EPSS changes.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2026-21637

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-05-22 0.02% 0.06% +0.04%
2 2026-01-21 — 0.02% —

Full EPSS history (2 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-21637

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.5 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 3.6 [email protected]
5.9 3.0 MEDIUM
CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 2.2 3.6 [email protected]

Weakness enumeration for CVE-2026-21637

OS Trackers for CVE-2026-21637

vendor priority summary link
alpine — CVE-2026-21637: 1 source package rows (nodejs); 209 state rows across 6 repos (3.19-main, 3.20-main, 3.21-main, 3.22-main, 3.23-main, edge-main); fixed 7, open 202. https://security.alpinelinux.org/vuln/CVE-2026-21637
debian not yet assigned CVE-2026-21637 not yet assigned priority: Debian including 1 source packages (nodejs), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2026-21637
redhat medium — https://access.redhat.com/security/cve/CVE-2026-21637
suse medium CVE-2026-21637 severity moderate: SUSE including 73 source package names (2.1.3-6.15:qemu-guest-agent-8.2.9-1.1, corepack20-20.20.0-150600.3.15.1, …), 164 product×package rows across 29 product lines (Container suse/sl-micro/6.0/kvm-os-container, Image SL-Micro, … (29 product lines)): Fixed 154, First Fixed 10. https://www.suse.com/security/cve/CVE-2026-21637/
ubuntu medium CVE-2026-21637 medium priority: Ubuntu including 1 source packages (nodejs), 9 status rows across 9 suites (bionic, focal, jammy, noble, plucky, questing, trusty, upstream, xenial): needs-triage 7, ignored 1, released 1. https://ubuntu.com/security/CVE-2026-21637

Affected software / configurations for CVE-2026-21637

Vendor Product Version Raw CPE
nodejs node.js >= 4.0.0, < 20.20.0 cpe:2.3:a:nodejs:node.js:*:*:*:*:-:*:*:*
nodejs node.js >= 22.0.0, < 22.22.0 cpe:2.3:a:nodejs:node.js:*:*:*:*:-:*:*:*
nodejs node.js >= 24.0.0, < 24.13.0 cpe:2.3:a:nodejs:node.js:*:*:*:*:-:*:*:*
nodejs node.js >= 25.0.0, < 25.3.0 cpe:2.3:a:nodejs:node.js:*:*:*:*:-:*:*:*

References for CVE-2026-21637

cvelogic Threat Intelligence