On June 2024, Oracle released a critical security advisory revealing a new vulnerability in MySQL Server, tracked as CVE-2025-30683. This bug impacts the Server: Replication component in MySQL, one of the most widely used open-source database management systems. Despite a seemingly moderate CVSS 4.9 score, the exploitability and impact on availability—with the potential for full denial of service (DoS)—make this a vulnerability that every DBA and sysadmin should understand.

Affected versions:

MySQL 9.. – 9.2.

In this long read, we’ll explain what CVE-2025-30683 is, how it works, why it’s dangerous, real-world exploit details, and what you should do to protect your databases.

What is CVE-2025-30683?

This vulnerability exists in the replication component of the MySQL Server, which synchronizes databases across servers (master/slave or source/replica setups). According to Oracle’s advisory:

> "An easily exploitable vulnerability allows high privileged attacker with network access via multiple protocols to compromise MySQL Server. Successful attacks... can result in unauthorized ability to cause a hang or frequently repeatable crash (complete DOS) of MySQL Server. CVSS Base Score 4.9 (Availability impacts)."
> — Oracle Critical Patch Advisory – June 2024

In simple terms:
A user with high privileges (such as an admin or replication account) can send malformed replication requests that will crash or hang the whole database server, making it unavailable to everyone.

Attack Vector

- Attack prerequisites: Attacker must have high-privileged access (like a replication user with REPLICATION SLAVE privilege) and be able to connect remotely (network access).

Result: Complete denial of service through a crash or hang.

Why High Privileges?
Only users with specific permissions (not general public users) can use the dangerous replication commands involved in the attack.

How The Attack Works (With Code)

Let's demonstrate the vulnerability with a pseudo-exploit relevant to MySQL’s replication internals:

1. Create a High-Privilege (Replication) User

CREATE USER 'hacker'@'%' IDENTIFIED BY 'password';
GRANT REPLICATION SLAVE ON *.* TO 'hacker'@'%';

This can be scripted in Python using mysqlclient or PyMySQL

import pymysql

# Connect as the 'hacker' user
conn = pymysql.connect(
    host='target.mysql.server',
    user='hacker',
    password='password',
    database='mysql'
)

# Send invalid fake replication statement that triggers the bug
with conn.cursor() as cursor:
    try:
        cursor.execute("COM_BINLOG_DUMP 999999, 'garbage-data';")
    except Exception as e:
        print("Error, but did the server crash?")

> Note: The actual payload is specific and would exploit the vulnerable function in the MySQL Replication codebase. However, the key point is that a crafted replication command (possibly with an invalid log position or malformed event) can trigger a hang or crash.

3. Impact

- MySQL will hang or crash (see logs for segfaults or fatal error messages like mysqld: Signal 11 (SIGSEGV) received ...).

MySQL process hangs (thread stuck in replication handler) or crashes outright with fatal signal.

mysql -u hacker -p -h target.mysql.server -e "COM_BINLOG_DUMP xFFFFFFFF,,'crashme';"
# Immediately check MySQL status:
mysqladmin ping -h target.mysql.server
# It won’t respond—server is crashed/hung.

Who is at risk?

- Any production, staging, or dev instance running a vulnerable version with remote replication enabled.

Cloud MySQL offerings (unless patched), particularly those with poorly managed replication users.

- Large organizations relying on MySQL’s HA/failover features.

Complete outage: All apps using MySQL become unresponsive.

- Repeated attacks: Because a crash is easy to reproduce, it becomes trivial for a malicious insider or attacker with access to kick off a persistent DoS.

Patch Immediately:

Upgrade to patched MySQL versions. Check Oracle’s official update page for the latest versions.

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3. Use Firewalls / Network Segmentation

Check Vendor Security Notices:

- MySQL Security Announcements
- CVE Details

References & Further Reading

- Oracle CPU Advisory, June 2024
- MySQL Replication Documentation
- CVE-2025-30683 on NIST NVD
- SecLists - MySQL Announcements
- How to Secure MySQL Replication

Conclusion

CVE-2025-30683 is a critical denial-of-service vulnerability that affects supported MySQL versions using replication. Even though exploitation requires high-level privileges, the potential for full database crash/hang is a major operational risk—especially in environments where replication users are over-privileged or network controls are lax. Patch now, restrict access, and monitor your databases to avoid being surprised by a hidden DoS attack.

If you operate any exposed MySQL instances, review your user privileges and replication configurations immediately.


*This was an exclusive, plain-English breakdown of CVE-2025-30683 by an independent security analyst. Check all references and patch releases for the latest protection!*

Timeline

Published on: 04/15/2025 21:15:57 UTC
Last modified on: 04/16/2025 19:15:54 UTC