CVE-2022-43705: A Security Vulnerability in Botan Before 2.19.3 that Allows the Forgery of OCSP Responses Due to a Certificate Verification Error

A security vulnerability, identified as CVE-2022-43705, affects Botan before 2.19.3 and potentially impacts a large number of systems and applications that rely on Botan for secure communication. Botan is an open-source cryptography library that provides a wide range of cryptographic algorithms, including TLS (Transport Layer Security), x509v3 certificates, and secure random number generation. The vulnerability allows an attacker to forge OCSP (Online Certificate Status Protocol) responses, thereby impacting the integrity and security of systems that rely on Botan for certificate verification.

The vulnerability was introduced in version 1.11.34 of Botan, which was released in November 2016. This post will provide details on the exploit, code snippets, and discuss the potential risks associated with the vulnerability.

Exploit Details

The vulnerability is located in the OCSP response handling logic, where a certificate verification error leads to the possibility of the forged OCSP responses. OCSP is a protocol used to determine the revocation status of x509 certificates, which are crucial for establishing secure SSL/TLS communications. A successful exploit allows an attacker to generate fake OCSP responses indicating that a certificate is still valid even if it has been revoked, thereby deceiving systems into accepting a revoked certificate as valid.

Here is an example of a typical OCSP request and response

// OCSP request
OCSP::Request req(certpath, issuer);
auto response = OCSP::online_check(req);

// OCSP response
if (response.status() == OCSP::Status_Code::Good)
{
    // The certificate is valid
}
else if (response.status() == OCSP::Status_Code::Revoked)
{
    // The certificate has been revoked
}
else
{
    // Unknown or error
}

The vulnerability can be exploited by compromising the certificate's issuer, or a malicious user with the ability to intercept and modify OCSP requests and responses. Such a user could forge a response indicating the certificate is in good standing, even though it should have been revoked.

The following references provide more information about the vulnerability

1. CVE Details: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2022-43705
2. Botan GitHub Repository: https://github.com/randombit/botan
3. Original Release Notes: https://botan.randombit.net/news.html

Mitigation and Recommendations

To mitigate this issue, users of Botan should update their systems to the latest version (2.19.3 or later) as soon as possible. This version includes a fix for the vulnerability. Upgrading can be done by simply building the latest version of Botan from the source code or using a package manager, such as Apt or Yum, to install the updated packages.

Additionally, application developers that use Botan should ensure that their implementation properly validates OCSP responses. Certificates should not be trusted solely based on a positive OCSP response; additional checks, such as verifying the certificate chain and revocation status using other protocols like CRL (Certificate Revocation Lists), should also be performed.

In summary, CVE-2022-43705 is a security vulnerability in Botan that allows the forgery of OCSP responses due to a certificate verification error. It is important for users of Botan to update their systems to the latest version and ensure their applications are properly validating OCSP responses to maintain the security and integrity of their systems.

Timeline

Published on: 11/27/2022 04:15:00 UTC
Last modified on: 12/01/2022 19:20:00 UTC