CVE-2026-93601: rustls webpki 0.101.0 before 0.103.12 Name Constraint Bypass

Severity: low (CVSS 2.2 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-09-18 · updated 2026-09-22
Weakness: CWE-295

Description

rustls-webpki (the Rust webpki fork used by rustls) versions >= 0.101.0 and prior to 0.103.12 and 0.104.0-alpha.6 incorrectly accepted permitted-subtree DNS name constraints for certificates asserting a wildcard name. For example, a name constraint of accept.example.com was treated as satisfied by a certificate for *.example.com, which could feasibly assert reject.example.com — a name outside the permitted subtree. Because name constraints are restrictions applied to otherwise properly issued certificates, the issue is only reachable after signature verification succeeds and requires a misissued wildcard certificate to exploit.

Affected products

rustls webpki: from 0.101.0 before 0.103.12; from 0.104.0-alpha.1 before 0.104.0-alpha.6 — fixed in 0.103.12, 0.104.0-alpha.6

How to fix

Upgrade to a fixed version: rustls webpki 0.103.12, 0.104.0-alpha.6. Check the vendor advisory for mitigations.

References

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