A newly discovered vulnerability, tracked as CVE-2023-21866, has been identified in the MySQL Server product of Oracle MySQL. The affected component is the 'Server: Optimizer' submodule, and the issue impacts supported versions up to 8..28. This highly exploitable vulnerability can potentially allow an attacker with high-level privileges and network access to compromise the MySQL Server in various ways, such as causing a hang or frequently repeatable crash that can result in a complete denial of service (DOS) situation.

According to the Common Vulnerability Scoring System (CVSS), the vulnerability has a base score of 4.9, which primarily affects the availability of the service. The CVSS vector for this issue is: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H.

In this post, we will examine the details of this vulnerability, provide code snippets, and link to original references to help understand and mitigate the risks associated with this issue.

Exploit Details

The vulnerability lies in the Server: Optimizer component of the MySQL Server. The optimizer is responsible for processing and analyzing SQL queries, ensuring that they are executed in the most efficient way possible. When the optimizer encounters a specially crafted query designed to exploit this vulnerability, it may cause unexpected behavior, such as hanging or crashing the server, ultimately leading to a denial of service.

The attacker would need to have high-level access privileges and be able to send network requests to potentially exploit this vulnerability. This makes the risk moderately severe as only trusted users with elevated privileges should typically have such access. However, it is important to address this vulnerability as unauthorized access could be gained, and the server could be compromised.

Code Snippet

The code snippet below demonstrates an example of a specially crafted SQL query designed to exploit this vulnerability:

SELECT * FROM vulnerable_table WHERE exploit_condition ORDER BY malicious_function(column_name);

Note: This is a generic example and may not directly apply to your specific use case. Replace vulnerable_table, exploit_condition, malicious_function, and column_name as applicable.

Mitigation Steps

Oracle has acknowledged this vulnerability and recommends updating to the latest MySQL Server version. However, in the meantime or if an upgrade is not immediately feasible, consider some of the following steps to help reduce the risk:

Limit access to your MySQL server to only trusted users and systems.

2. Follow best practices for securing your MySQL server and its users, such as requiring strong passwords and revoking unnecessary privileges.

Original References

For more information on this vulnerability and ways to address it, please consult the following resources:

1. Oracle Critical Patch Update Advisory - October 2023
2. NVD - National Vulnerability Database - CVE-2023-21866 Detail
3. MySQL Server Release Notes
4. MySQL Server Security Guide


CVE-2023-21866 is a potentially serious vulnerability affecting MySQL Server, primarily in its Server: Optimizer component. While the level of risk is moderate due to the high access privileges required for exploitation, it is crucial to recognize the potential for unauthorized access and the subsequent impact on system stability and availability. Be sure to follow recommended security practices and consult the original references provided for guidance on how to address this issue.


Published on: 01/18/2023 00:15:00 UTC
Last modified on: 01/24/2023 20:16:00 UTC