CVE-2022-4203 refers to a read buffer overrun vulnerability found in the X.509 certificate verification process, particularly in the name constraint checking. The buffer overrun might lead to crashes and, subsequently, a denial-of-service (DoS) attack. In some cases, it could result in the disclosure of private memory contents, such as private keys or sensitive plaintext, although no working exploit has been discovered for this as of now.

Exploit Details

This vulnerability occurs specifically during the name constraint checking during X.509 certificate verification (_after_ the certificate chain signature verification). It requires one of two conditions:

A Certificate Authority (CA) has signed the malicious certificate.

2. The application continues certificate verification despite the failure to construct a path to a trusted issuer.

In a TLS client scenario, this vulnerability can be exploited when connecting to a malicious server. On the other hand, in a TLS server setting, this can be exploited if the server requests client authentication and a malicious client connects.

Below is a simplified example of vulnerable code for educational purposes

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "x509.h"

// Vulnerable function
int name_constraints_check(...) {
    size_t buffer_size = ...;
    unsigned char *buffer = calloc(1, buffer_size);
    // Buffer overrun might happen in the following code block
    for (...) {
        size_t name_length = ...;
        memcpy(buffer + offset, name_ptr, name_length);
        offset += name_length;


To fix this vulnerability, an application should ensure proper buffer size calculation and boundary checks during the name constraint checking step in X.509 certificate verification. Moreover, applications should stop certificate verification if it fails to construct a path to a trusted issuer.

Original References

1. NVD - CVE-2022-4203
2. US-CERT Vulnerability Note VU#354143
3. OpenSSL Security Advisory: x509: read buffer overrun in name constraint checking (CVE-2022-4203)

It is essential to stay informed about security advisories related to the libraries and applications you use. Regularly applying security updates can significantly reduce the risks associated with vulnerabilities like CVE-2022-4203.

Additionally, it is advisable for developers to apply secure coding practices to minimize the chances of introducing such vulnerabilities in the first place. A thorough understanding of memory management, buffer overflows, and secure coding practices can help protect your applications from attacks that aim to exploit such vulnerabilities.


Published on: 02/24/2023 15:15:00 UTC
Last modified on: 03/09/2023 20:03:00 UTC