RUSTSEC-2026-0099: Name constraints were accepted for certificates asserting a wildcard name

| Details | |
| --- | --- |
| Package | `rustls-webpki` |
| Version | `0.101.7` |
| URL | n/a |
| Patched Versions | >=0.103.12, <0.104.0-alpha.1 OR >=0.104.0-alpha.6 |
| Aliases | [GHSA-xgp8-3hg3-c2mh](https://github.com/advisories/GHSA-xgp8-3hg3-c2mh) |

Permitted subtree name constraints for DNS names were accepted for certificates asserting a wildcard name.

This was incorrect because, given a name constraint of `accept.example.com`, `*.example.com` could feasibly allow a name of `reject.example.com` which is outside the constraint.
This is very similar to [CVE-2025-61727](https://go.dev/issue/76442).

Since name constraints are restrictions on otherwise properly-issued certificates, this bug is reachable only after signature verification and requires misissuance to exploit.

This vulnerability is identified as [GHSA-xgp8-3hg3-c2mh](https://github.com/rustls/webpki/security/advisories/GHSA-xgp8-3hg3-c2mh). Thank you to @1seal for the report.