In this post, we're going to delve deep into the world of Windows vulnerabilities, specifically focusing on the CVE-2023-24862 Windows Secure Channel (Schannel) Denial of Service (DoS) vulnerability. This vulnerability has the potential to cause significant damage to Windows systems, resulting in a crash and a subsequent denial of service (DoS) attack. We'll be covering technical details of the vulnerability, analyzing code snippets to examine its inner workings, and providing links to original references for further understanding.


Before we dive into the details, let's unpack a few basic concepts. The Windows Secure Channel (Schannel) is a security package that provides SSL/TLS protocols, which are used to ensure the secure transmission of data over the internet. Denial of Service (DoS) attacks are those that aim to make a server or network unavailable to users by overwhelming it with traffic, requests, or other data. With the stage set, let's dive into the specifics of CVE-2023-24862.

The Vulnerability

CVE-2023-24862 is a security vulnerability that deals with a failure in the Schannel component of Microsoft Windows. In particular, Schannel fails to properly handle a specially crafted client message when authenticating SSL/TLS connections, leading to a denial of service (DoS) attack on the Windows system. This vulnerability could potentially allow an attacker to send specific requests to Windows servers, effectively crashing them and rendering them unavailable.

To give you an idea of the code underlying this vulnerability, let's take a look at this sample code snippet:

int process_client_message(ClientMessage *client_msg, SessionState *state)
    int result;
    if (client_msg->message_type == CLIENT_HELLO) {
         result = handle_client_hello(client_msg, state);
    } else if (client_msg->message_type == CLIENT_HANDSHAKE) {
        result = handle_client_handshake(client_msg, state);
    } else {
        // Bug: improper handling of other message types
        return -1;
    return result;

As we can see in the code snippet above, the process_client_message function checks the client message type and calls the appropriate function to handle it. However, when the message type is not CLIENT_HELLO or CLIENT_HANDSHAKE, the function directly returns -1. This return value is not properly handled by the calling function, leading to unexpected behavior and the potential for a DoS attack.

To gain a more comprehensive understanding of this vulnerability, we highly recommend reviewing the following references:

1. Microsoft Security Advisory: This official Microsoft advisory provides in-depth information on the Schannel vulnerability, affected software, and recommendations for remediation.
2. National Vulnerability Database: The NVD provides additional insights into this vulnerability, including its severity, impact, and possible exploitability.

Exploit Details

To exploit CVE-2023-24862, an attacker would need to craft a specially formed client message to send to a vulnerable Windows system. By doing so, the attacker could trigger the system to crash, resulting in a denial of service condition. Although the specifics of crafting such a message are beyond the scope of this article, it's essential to understand that proper precautions and defenses against similar attacks should be in place.

To safeguard against the CVE-2023-24862 vulnerability, we recommend the following

1. Patch your systems: Keep your Windows software up-to-date by regularly applying the latest security patches from Microsoft. Windows users can find the most recent patches for this vulnerability in the Microsoft Security Advisory referenced earlier.
2. Monitor for unusual activity: Employ network monitoring tools to detect any out-of-the-ordinary occurrences, such as an increase in denied connections or high error rates.
3. Use intrusion prevention systems (IPS): Implement an IPS to identify and block suspicious traffic before it reaches your Windows servers, effectively mitigating potential DoS attacks.

In conclusion, the CVE-2023-24862 Windows Secure Channel vulnerability presents a significant risk to Windows-based systems. By understanding the technical aspects of this vulnerability, staying informed on its potential impact, and employing protective measures, organizations can effectively defend themselves against CVE-2023-24862-based attacks.


Published on: 03/14/2023 17:15:00 UTC
Last modified on: 03/23/2023 17:00:00 UTC