Rust Security Patch: webpki Crate Fixes DNS Name Constraint Bypass (GHSA-xgp8-3hg3-c2mh)

A critical security flaw in the widely used Rust cryptography library `webpki` has been patched, addressing a vulnerability that could allow a certificate with a wildcard name to bypass DNS name constraints. The bug, tracked as GHSA-xgp8-3hg3-c2mh, incorrectly accepted permitted subtree name constraints for DNS names in certificates asserting a wildcard. This means a certificate for `*.example.com` could be incorrectly validated under a name constraint intended to only allow `accept.example.com`, potentially permitting a name like `reject.example.com` that should be blocked.

The vulnerability is a logic error in the library's name constraint validation, making it similar to the recently disclosed CVE-2025-61727 in the Go ecosystem. The `webpki` crate is a core dependency for the `rustls` TLS library, making this update essential for any Rust project handling secure connections. The patch updates the crate from version 0.103.10 to 0.103.12.

Exploitation is complex, requiring both a misissued certificate and the specific name constraint validation failure, which occurs after successful signature verification. The official CVSS 3.1 score is a low 2.2, reflecting the high attack complexity and privileged position required. However, the flaw represents a subtle but significant weakening of the intended security boundary for applications that rely on strict certificate name constraints. Developers are urged to update their workspace dependencies immediately to mitigate this risk.