A flaw in Node.js TLS hostname verification allows a certificate with only a DNS SAN to authenticate an IP endpoint when the client connects using a non-canonical IPv4 spelling, such as `0177.0.0.1`, `0x7f.0.0.1`, `2130706433` or `127.1`. `tls.checkServerIdentity()` did not classify these hosts as IP addresses, but normalized them to their canonical form and matched the result against the certificate DNS names. A certificate containing `DNS:127.0.0.1` and no `IP Address:127.0.0.1` SAN was therefore accepted, while the same certificate is correctly rejected for `127.0.0.1`. Exploitation requires a certificate with a numeric DNS SAN issued by a CA trusted by the client, and a platform resolver that accepts these spellings, such as glibc. This vulnerability affects Node.js 26.x, 24.x, and 22.x.

MediumVendor CVSS 6.7 / 10 1 CVE Published Oct 25, 2026 at 1:02 AM UTC

Summary

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Release Notes

Oct 25, 2026 at 1:02 AM UTC
Published by Microsoft Security Response Center
The publication date reported by the vendor.
Oct 26, 2026 at 2:50 PM UTC
Updated by Microsoft Security Response Center
The vendor changed the advisory after it was first published.
Oct 27, 2026 at 9:20 AM UTC
Added to SecurityAlert
We collected the advisory from the official source.
Oct 27, 2026 at 9:40 PM UTC
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Details collected from Microsoft Security Response Center.

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