# CVE-2026-93601: rustls-webpki name constraint bypass for wildcard certificates

Source: https://junglewise.ai/threats/cve-2026-93601-rustls-webpki-name-constraint-bypass-for-wildcard-certificates  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-18. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

CVE-2026-93601 · Severity: low · CVSS 3.1 · Published 2026-09-18

rustls-webpki is a certificate validation library used by the Rust TLS implementation. A flaw in name constraint validation allows wildcard certificates to bypass DNS name restrictions that were otherwise properly issued. An attacker with a misissued wildcard certificate could assert domain names outside their permitted scope, potentially enabling domain impersonation attacks.

Technologies: [rustls-webpki (crates.io)](https://junglewise.ai/threats/technologies/rustls-webpki), [Rustls Webpki](https://junglewise.ai/threats/technologies/webpki). Vendors: [crates.io](https://junglewise.ai/threats/vendors/crates-io), [Rustls](https://junglewise.ai/threats/vendors/rustls).

## Quick answers

**Is CVE-2026-93601 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-93601 being exploited in the wild.

**How severe is CVE-2026-93601?** Low severity, with a CVSS score of 3.1, published 18 September 2026.

**Which products and versions are affected?** rustls-webpki (crates.io) SEMVER:introduced=0.0.0-0,fixed=0.103.12,introduced=0.104.0-alpha.1,fixed=0.104.0-alpha.6, SEMVER:introduced=0.101.0,fixed=0.103.12; Rustls Webpki >= 0.101.0, < 0.103.12; >= 0.104.0-alpha.1, < 0.104.0-alpha.6.

**Is there a fix for CVE-2026-93601?** Yes. rustls-webpki (crates.io): upgrade to 0.103.12, 0.104.0-alpha.6 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-93601 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-93601?** Check whether you run rustls-webpki (crates.io) or Rustls Webpki at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- rustls-webpki (crates.io): upgrade to 0.103.12, 0.104.0-alpha.6 or later

  ```sh
  cargo update -p rustls-webpki
  ```


## Technical details

The vulnerability is an improper certificate validation (CWE-295) in name constraint handling. When a certificate asserts a wildcard DNS name (e.g., *.example.com), the library incorrectly accepted permitted-subtree name constraints as satisfied. For example, a constraint of accept.example.com would be satisfied by *.example.com, which could feasibly cover reject.example.com—a name outside the permitted subtree. This occurs only after signature verification succeeds and requires a misissued wildcard certificate to reach. Patches are available in versions 0.103.12 and 0.104.0-alpha.6 or later.

## Affected products

- rustls webpki >= 0.101.0, < 0.103.12; >= 0.104.0-alpha.1, < 0.104.0-alpha.6

## Identifiers

- CVE-2026-93601
- GHSA-xgp8-3hg3-c2mh
- RUSTSEC-2026-0099

## Timeline

- 2026-04-15: disclosed: GitHub security advisory published
- 2026-09-18: advisory: CVE-2026-93601 published

## References

- [https://github.com/rustls/webpki/security/advisories/GHSA-xgp8-3hg3-c2mh](https://github.com/rustls/webpki/security/advisories/GHSA-xgp8-3hg3-c2mh)
- [https://www.vulncheck.com/advisories/rustls-webpki-0.101.0-before-0.103.12-name-constraint-bypass](https://www.vulncheck.com/advisories/rustls-webpki-0.101.0-before-0.103.12-name-constraint-bypass)

## Related threats

- [Go crypto/x509 untrusted intermediate certificate validation](https://junglewise.ai/threats/cve-2026-111943-on-most-platforms-go-uses-the-given-system-root-certificates)
- [rustls-webpki CRL distribution point matching bypass](https://junglewise.ai/threats/cve-2026-93602-rustls-webpki-crl-distribution-point-matching-bypass)
- [rustls-webpki X.509 name constraint bypass for URI names](https://junglewise.ai/threats/cve-2026-93600-rustls-webpki-x-509-name-constraint-bypass-for-uri-names)
- [rustls-webpki integer underflow in BIT STRING parsing](https://junglewise.ai/threats/cve-2026-93599-rustls-webpki-integer-underflow-in-bit-string-parsing)
- [rustls-webpki: CPU denial of service in certificate path building](https://junglewise.ai/threats/rustls-webpki-cpu-denial-of-service-in-certificate-path-building-3f07ea21)