CVE-2026-69248: pyca cryptography improper certificate validation in Name Constraints

Executive brief

A vulnerability exists in the 'cryptography' library, a widely used Python package for secure communication and data protection. The library's certificate verification process incorrectly handles wildcard domain names when restricted by specific security constraints. This could allow a malicious actor to use a certificate for a domain they are not authorized to represent, potentially leading to unauthorized access or the interception of sensitive data.

Technical details

A vulnerability in the X.509 verification logic of the 'cryptography' library (pyca/cryptography) allows for a Name Constraints escape. When an intermediate CA is restricted to a specific permittedSubtree (e.g., foo.example.com), the verifier incorrectly accepts a leaf certificate containing a wildcard SAN (e.g., *.example.com). This bypasses the restrictions defined in RFC 5280 §4.2.1.10, as the verifier may treat the leaf as authoritative for domains outside the constrained scope (e.g., bar.example.com). The issue is rooted in the DNSConstraint::matches implementation and is fixed in version 49.0.0.

Affected products

• pyca cryptography <= 48.0.0

Timeline

• 2026-07-31: disclosed
• 2026-08-03: advisory
• 2026-08-03: patched

References

• https://api.github.com/users/randombit
• https://github.com/randombit
• https://api.github.com/users/randombit/gists%7B/gist_id%7D
• https://api.github.com/users/randombit/repos
• https://avatars.githubusercontent.com/u/469092?v=4
• https://api.github.com/users/randombit/events%7B/privacy%7D