Node.js TLS callback exception handling DoS
CVE-2026-21637 is a Node.js TLS error-handling vulnerability affecting TLS server code paths that invoke callback logic during the handshake. The provided content states that synchronous exceptions thrown from pskCallback or ALPNCallback can bypass normal TLS error handling (tlsClientError and error), resulting in either immediate process termination or silent file descriptor leaks. Supporting context also describes a related/incomplete-fix condition in _tls_wrap.js where callback invocation paths such as loadSNI() / SNICallback lacked protective try/catch wrapping, allowing attacker-controlled handshake input to trigger uncaught exceptions. Because these callbacks process remote client-supplied TLS handshake data, an unauthenticated attacker can repeatedly connect and trigger the vulnerable path, causing denial of service.
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Impact, mitigation & remediation
What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.
Impact
What an attacker gets, and what they’ve been doing with it.
Mitigation
If you can’t patch tonight, do this now.
pskCallback and ALPNCallback where feasible. Where those callbacks are required, ensure callback implementations defensively validate attacker-controlled input and do not allow synchronous exceptions to escape; wrap callback logic in local try/catch handling and fail closed without throwing. Additional operational mitigations such as connection throttling, handshake rate limiting, and file descriptor/resource monitoring can reduce exploit reliability but do not eliminate the underlying flaw.Remediation
Patch, then assume compromise.
Exploits
No public exploits tracked yet. Mallory keeps watching.
No public exploit code observed for this vulnerability.
Affected products & vendors
Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.
Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.
Recent activity
23 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
A non-Microsoft-issued CVE impacting Node.js, mentioned as included among the addressed flaws.
A Node.js TLS-layer improper exception handling vulnerability involving loadSNI()/SNICallback that can cause an uncaught exception and remote denial of service; the article describes this as an incomplete fix scenario.
A high-severity Node.js TLS error-handling flaw in SNICallback that can be triggered remotely without authentication to crash the Node.js process.
Medium-severity issue in Node.js TLS where PSK/ALPN callback exceptions can crash servers (DoS) or leak file descriptors.
The version that knows your environment.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.