CVE-2025-21566
📋 TL;DR
This vulnerability in Oracle MySQL Server's optimizer component allows attackers with low-privileged network access to cause a denial of service (DoS) by crashing or hanging the server. It affects MySQL Server versions 9.1.0 and earlier. The vulnerability is easily exploitable via multiple network protocols.
💻 Affected Systems
- Oracle MySQL Server
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete unavailability of MySQL Server leading to application downtime and service disruption.
Likely Case
Frequent server crashes requiring manual restarts, causing intermittent service outages.
If Mitigated
Limited impact if network access is restricted and proper authentication controls are in place.
🎯 Exploit Status
CVSS indicates low attack complexity; requires low-privileged credentials but no user interaction.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check Oracle Critical Patch Update Advisory for specific fixed version
Vendor Advisory: https://www.oracle.com/security-alerts/cpujan2025.html
Restart Required: Yes
Instructions:
1. Review Oracle Critical Patch Update Advisory for January 2025. 2. Apply the recommended patch for MySQL Server. 3. Restart MySQL service after patching.
🔧 Temporary Workarounds
Restrict Network Access
allLimit MySQL server access to trusted IP addresses only
Configure MySQL bind-address to specific IPs in my.cnf
Use firewall rules to restrict MySQL port (default 3306) access
Minimize User Privileges
allApply principle of least privilege to MySQL user accounts
REVOKE unnecessary privileges from low-privileged users
GRANT only required permissions for specific databases/tables
🧯 If You Can't Patch
- Implement strict network segmentation and firewall rules to limit MySQL access
- Monitor for unusual connection patterns and server crash events
🔍 How to Verify
Check if Vulnerable:
Check MySQL version: SELECT VERSION(); If version is 9.1.0 or earlier, system is vulnerable.Check Version:
mysql --version or SELECT VERSION();Verify Fix Applied:
Verify MySQL version is updated beyond 9.1.0 and check Oracle advisory for specific fixed version.📡 Detection & Monitoring
Log Indicators:
- MySQL error logs showing unexpected crashes
- Authentication logs showing failed connection attempts from unusual sources
- Process monitoring showing MySQL service restarts
Network Indicators:
- Unusual traffic patterns to MySQL port 3306
- Multiple connection attempts from single sources
SIEM Query:
source="mysql.log" ("crash" OR "segmentation fault" OR "aborted")