CVE-2022-3786: Buffer Overrun Vulnerability in X.509 Certificate Verification - Name Constraint Checking

A recently discovered vulnerability, tracked as CVE-2022-3786, has the potential to cause considerable disruption in systems that utilize X.509 certificates for verification. This vulnerability revolves around a buffer overrun that can be triggered in the name constraint checking stage of X.509 certificate verification. While exploiting this vulnerability requires a level of sophistication, it is critical that developers and system administrators address the issue to prevent service disruptions and potential security breaches.

Exploit Details

The buffer overrun occurs during the name constraint checking stage of X.509 certificate verification, specifically after the certificate chain signature verification. To exploit this vulnerability, an attacker needs either a Certificate Authority (CA) to sign a malicious certificate or an application that continues the certificate verification process despite not being able to construct a path to a trusted issuer.

By crafting a malicious email address within a certificate, the attacker can overflow an arbitrary number of bytes containing the . character (decimal 46) on the stack. The resulting buffer overflow might cause a crash, resulting in a denial of service for the affected system or application. It is important to note that this vulnerability can be exploited in both TLS clients and servers, as outlined below:

In a TLS client, connecting to a malicious server can trigger the vulnerability.

2. In a TLS server requesting client authentication, the vulnerability can be triggered when a malicious client connects.

Let's take a look at a sample code snippet that demonstrates the potential buffer overrun

// Check for buffer overflow
size_t required_buffer_size = end_of_name - start_of_name + 1;
if (required_buffer_size > buffer_size) {
    // Buffer overflow occurs here, causing a crash and potential denial of service.
    memcpy(buffer, start_of_name, buffer_size - 1);
    buffer[buffer_size - 1] = '\';
} else {
    memcpy(buffer, start_of_name, required_buffer_size - 1);
    buffer[required_buffer_size - 1] = '.';
    buffer[required_buffer_size] = '\';
}

In this code snippet, required_buffer_size represents the size of the buffer necessary to copy the data from start_of_name to end_of_name. The problem arises when the buffer cannot accommodate the transfer; the memcpy function doesn't take into account the missing bytes, leading to a buffer overrun.

For more information about the CVE-2022-3786 vulnerability, please consult the following sources

- CVE - CVE-2022-3786
- NVD - CVE-2022-3786 Detail

Conclusion

It is crucial for developers and system administrators to be aware of and take the necessary precautions to protect their systems against CVE-2022-3786. The buffer overrun vulnerability in the name constraint checking stage of X.509 certificate verification could lead to a denial of service, causing disruption and potential security breaches. Systems that utilize X.509 certificates should be patched or configured to address this issue as soon as possible.

Timeline

Published on: 11/01/2022 18:15:00 UTC
Last modified on: 11/04/2022 12:15:00 UTC