CVE-2023-0465: A Non-default Certificate Verification Issue Paving the Way for Malicious Attacks

A security vulnerability, known as CVE-2023-0465, has been discovered in OpenSSL, a widely-used software library that provides cryptographic functionalities for securing communication over networks. This vulnerability affects applications that utilize non-default certificate verification options. As a result, malicious Certificate Authority (CA) can leverage this weakness to bypass certain security checks, which may lead to potentially harmful breaches and unauthorized access.

Main Content

The issue revolves around the improper handling of invalid certificate policies in leaf certificates by OpenSSL. Instead of registering an error, invalid policies are just ignored, allowing a malicious CA to deliberately assert such policies and circumvent policy checking procedures. It's worth noting that policy processing is disabled by default and has to be intentionally enabled by users, either by providing a -policy argument when invoking command line utilities or by invoking the X509_VERIFY_PARAM_set1_policies() function in an application's code.

Here's an example of how the vulnerability can be exploited

- A malicious CA generates a certificate chain containing invalid certificate policies in a leaf certificate.
- The target application enables policy processing, for instance, by calling the X509_VERIFY_PARAM_set1_policies() function as shown in the code snippet below:
 

  X509_VERIFY_PARAM *vpm;
  STACK_OF(ASN1_OBJECT) *policies;
  ASN1_OBJECT *policy;

  vpm = X509_VERIFY_PARAM_new();
  policies = sk_ASN1_OBJECT_new_null();
  policy = OBJ_txt2obj("1.3.6.1.4.1.11129.2.4.2", 1);

  sk_ASN1_OBJECT_push(policies, policy);
  X509_VERIFY_PARAM_set1_policies(vpm, policies);
  

- In this scenario, the target application would not reject the certificate chain even though it contains invalid certificate policies. The attacker may now leverage this security oversight to conduct further malicious activities such as MITM (Man-In-The-Middle) attacks.

Original references

- OpenSSL Security Advisory on CVE-2023-0465: Link
- CVE-2023-0465: Link
- X509_VERIFY_PARAM_set1_policies() function documentation: Link

Attack Complexity: Low

- Pre-requisites: Policy processing must be enabled; Attacker must obtain a leaf certificate with invalid policies from a malicious CA.
- Impact: An attacker can leverage this vulnerability to bypass certificate policy checking, which might lead to unauthorized access and other related security threats.

In conclusion, this vulnerability demonstrates the potential risks associated with using non-default options in certificate verification processes. Therefore, software developers and system administrators should exercise caution and follow best practices when implementing security measures. Additionally, keeping software libraries and platforms up-to-date with the latest security patches is crucial to mitigate new threats and vulnerabilities.

Timeline

Published on: 03/28/2023 15:15:00 UTC
Last modified on: 04/14/2023 23:15:00 UTC