CVE-2026-21637: High severity nodejs/node vulnerability
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.
Other sources
CVE-2026-21637 is regarding a vulnerability 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. HackerOne created this CVE on their behalf. The documented Visual Studio updates incorporate updates in Node.js which address this vulnerability. Please see CVE-2026-21637 for more information.
— Microsoft
HackerOne: CVE-2026-21637 TLS PSK/ALPN Callback Exceptions Bypass Error Handlers
— Microsoft
Affected Software
Event History
Frequently Asked Questions
What is the severity of CVE-2026-21637?
CVE-2026-21637 is considered a high severity vulnerability due to its potential to crash or exhaust resources of a TLS server.
How do I fix CVE-2026-21637?
To fix CVE-2026-21637, upgrade your Node.js version to the latest release that addresses this vulnerability.
What are the attack vectors for CVE-2026-21637?
Remote attackers can exploit CVE-2026-21637 through callbacks like `pskCallback` or `ALPNCallback` during TLS operations.
Which versions of Node.js are affected by CVE-2026-21637?
CVE-2026-21637 affects specific versions of Node.js, particularly those that utilize the faulty TLS error handling mechanisms during the specified callbacks.
What kind of impact does CVE-2026-21637 have on a TLS server?
CVE-2026-21637 can lead to denial of service by crashing the server or exhausting its resources due to unhandled exceptions.