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CVE-2026-34073: cryptography has incomplete DNS name constraint enforcement on peer names

• Severity: medium (CVSS 5.3 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: 2026-03-31 · updated 2026-10-14
• Weakness: CWE-295

Description

cryptography is a package designed to expose cryptographic primitives and recipes to Python developers. Prior to version 46.0.6, DNS name constraints were only validated against SANs within child certificates, and not the "peer name" presented during each validation. Consequently, cryptography would allow a peer named bar.example.com to validate against a wildcard leaf certificate for *.example.com, even if the leaf's parent certificate (or upwards) contained an excluded subtree constraint for bar.example.com. This issue has been patched in version 46.0.6.

Affected products

• pyca cryptography: before 46.0.6 — fixed in 46.0.6
• Pypi Cryptography: before 46.0.6; 0.1, 0.2, 0.2.1, 0.2.2, 0.3, 0.4 (+145) — fixed in 46.0.6

How to fix

Upgrade to a fixed version: pyca cryptography 46.0.6; Pypi Cryptography 46.0.6. Check the vendor advisory for mitigations.

In the news

• VU#948176: Multiple TLS libraries can bypass delegation enforcement
• VU#573195: Go, OpenSSL, Apple, LibreSSL, pyca, wolfSSL Name-Constraint Inconsistency in RFC 5280 Implementation

References

• https://github.com/pyca/cryptography/security/advisories/GHSA-m959-cc7f-wv43
• https://www.kb.cert.org/vuls/id/948176

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