Botan OCSP Response Signature Verification Vulnerability Allows Certificate Revocation Bypass

A vulnerability in the Botan C++ cryptography library, affecting versions 3.0.0 prior to 3.11.0, allows a man-in-the-middle attacker to bypass certificate revocation checks. During X509 path validation, the library correctly assessed the status of OCSP responses but failed to verify the signatures of those responses. This oversight enables interception and tampering with OCSP response data without detection. The vulnerability arises because OCSP is typically deployed over plain HTTP, leaving it susceptible to interception through methods like DNS hijacking, BGP hijacking, or rogue network access points.

Impact

Exploitation of this vulnerability allows a man-in-the-middle attacker to manipulate OCSP response bodies undetected, effectively bypassing certificate revocation checks. This could lead to the acceptance of revoked certificates, potentially allowing fraudulent activities such as impersonating a legitimate entity or establishing a secure connection using a compromised certificate.

Remediation

Users can upgrade to Botan version 3.11.0 or later to address this vulnerability.