OCSP Signature Verification Bypass in Botan Library Causes Validation Risk

Executive Summary

This vulnerability exists in the Botan C++ cryptography library versions from 3.0.0 up to but not including 3.11.0. During the validation of X509 certificate paths, the library checked the status code of OCSP (Online Certificate Status Protocol) responses but failed to verify the signature on the OCSP response itself. This means that the authenticity of the OCSP response was not confirmed, potentially allowing an attacker to use forged or tampered OCSP responses.

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Impact Analysis

Because the signature on OCSP responses was not verified, an attacker could provide a fake OCSP response indicating that a revoked or invalid certificate is still valid. This could lead to acceptance of untrusted or malicious certificates during TLS or other cryptographic operations, potentially enabling man-in-the-middle attacks or other security breaches.

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Mitigation Strategies

The vulnerability in Botan versions from 3.0.0 to before 3.11.0 involves improper verification of OCSP response signatures during X509 path validation.

To mitigate this vulnerability, you should upgrade Botan to version 3.11.0 or later, where the issue has been patched.

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