Executive brief
rustls-webpki is a library used by Rust applications to validate X.509 certificates. The library failed to enforce name constraints on URI identifiers in certificates, allowing misissued certificates with URI names to bypass restrictions that should have been applied. Exploitation requires a misissued certificate to reach signature verification, making the practical risk low, though it could allow an attacker with certificate-issuing capability to create certificates that violate organizational policies.
Technical details
The vulnerability is a certificate validation bypass (CWE-295) in name constraint enforcement. rustls-webpki versions 0.101.0–0.103.11 and 0.104.0-alpha through 0.104.0-alpha.5 ignored X.509 name constraints for URI identifiers, accepting certificates that should have been rejected. The flaw exists in the name constraint validation logic and is only reachable after successful certificate signature verification. Exploitation requires a misissued certificate with URI names that violate applied name constraints. The library provides no public API for URI name assertion and URI name constraints are otherwise unimplemented, limiting real-world impact. Versions 0.103.12 and 0.104.0-alpha.6 and later reject URI name constraints unconditionally, fixing the issue.
Affected products
- Rustls webpki 0.101.0 through 0.103.11, 0.104.0-alpha.1 through 0.104.0-alpha.5
Timeline
- 2026-04-15: disclosed: GitHub Security Advisory (GHSA-965h-392x-2mh5) published
- 2026-04-15: patched: Versions 0.103.12 and 0.104.0-alpha.6 released with fix