Botan contains a flaw in its X.509 name constraint handling that allows a malicious certificate to bypass excluded DNS subtrees if the end‑entity certificate has no subject alternative name and the common name uses mixed‑case characters. This enables an attacker to forge a certificate that appears valid for a restricted domain while actually referencing an excluded domain, thereby compromising the integrity of certificate validation.

The vulnerability affects randombit Botan cryptographic library versions prior to 3.11.0. Any software that links against these versions is vulnerable. No specific operating system or platform limits are identified beyond the use of the affected Botan library.

The CVSS score of 5.9 indicates moderate severity, while the EPSS score is below 1% suggesting a low likelihood of current exploitation. The vulnerability is not listed in the CISA KEV catalog. Exploitation requires an attacker to generate or acquire a certificate chain containing a case‑variant CN without a subject alternative name and present it to a system performing X.509 validation with Botan. The flaw lies in certificate validation logic rather than code execution, so its impact is limited to trust bypass rather than arbitrary code execution. The attack vector is inferred to be through forged certificates and does not require additional software vulnerabilities.