CVE-2026-34073

In versions of cryptography prior to 46.0.5, 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 behavior resulted from a gap between RFC 5280 (which defines Name Constraint semantics) and RFC 9525 (which defines service identity semantics): put together, neither states definitively whether Name Constraints should be applied to peer names. To close this gap, cryptography now conservatively rejects any validation where the peer name would be rejected by a name constraint if it were a SAN instead.

In practice, exploitation of this bypass requires an uncommon X.509 topology, one that the Web PKI avoids because it exhibits these kinds of problems. Consequently, we consider this a medium-to-low impact severity.

See CVE-2025-61727 for a similar bypass in Go's crypto/x509.

Attribution

Reporter: @1seal

CVE-2026-34073 has a CVSS score of 5.3 (Low). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (46.0.6); upgrading removes the vulnerable code path.

Kodem intelligence

Users should upgrade to 46.0.6 or newer.

1. What is CVE-2026-34073? CVE-2026-34073 is a low-severity security vulnerability in cryptography (pip), affecting versions < 46.0.6. It is fixed in 46.0.6.
2. How severe is CVE-2026-34073? CVE-2026-34073 has a CVSS score of 5.3 (Low). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of cryptography are affected by CVE-2026-34073? cryptography (pip) versions < 46.0.6 is affected.
4. Is there a fix for CVE-2026-34073? Yes. CVE-2026-34073 is fixed in 46.0.6. Upgrade to this version or later.
5. Is CVE-2026-34073 exploitable, and should I be worried? Whether CVE-2026-34073 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-34073 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-34073? Upgrade cryptography to 46.0.6 or later.

Other vulnerabilities in cryptography