The vulnerability is in the DNSConstraint::matches method of python-cryptography. For library versions 45.0.0 through 48.0.0, the verifier incorrectly treats a wildcard DNS subject alternative name, such as *.example.com, as matching a more specific permitted DNS name allowed by an intermediate CA (like foo.example.com). Because the wildcard can resolve to sibling names such as bar.example.com, the library accepts a certificate chain that should be rejected, allowing a domain constraint bypass. This flaw permits invalid certificates and can lead to man‑in‑the‑middle or impersonation attacks. The weakness is a CWE‑295 error in authorization logic.

The python-cryptography package developed by the PyCA project is affected for all releases prior to version 49.0.0. Any application or service that imports this library for TLS/SSL certificate verification and is running an older version is vulnerable.

The CVSS score of 6.9 indicates a medium severity vulnerability, and the EPSS score indicates a very low exploitation probability (<1%), the flaw is not listed in the CISA KEV catalog. Exploitation is likely to occur in environments where python-cryptography performs hostname verification for TLS connections; an attacker who can supply a crafted certificate chain to a vulnerable application can cause the library to accept a chain that should be rejected, leading to unauthorized access or data compromise. The attack vector is inferred to be remote through application traffic that establishes TLS sessions using this library.