CVE-2025-21500: Oracle MySQL Server DoS Vulnerability

CVE-2025-21500 Overview

CVE-2025-21500 is a Denial of Service vulnerability in the MySQL Server product of Oracle MySQL, specifically affecting the Server: Optimizer component. This vulnerability allows a low-privileged attacker with network access to cause a complete denial of service condition, resulting in a hang or frequently repeatable crash of the MySQL Server.

The vulnerability is classified as easily exploitable, requiring only low privileges and network access via multiple protocols to successfully compromise affected MySQL Server instances. The impact is limited to availability, with no confidentiality or integrity implications.

Critical Impact
Successful exploitation enables attackers to cause complete denial of service of MySQL Server, disrupting database operations and potentially affecting all dependent applications and services.

Affected Products

Oracle MySQL Server 8.0.40 and prior
Oracle MySQL Server 8.4.3 and prior
Oracle MySQL Server 9.1.0 and prior

Discovery Timeline

2025-01-21 - CVE-2025-21500 published to NVD
2025-11-03 - Last updated in NVD database

Technical Details for CVE-2025-21500

Vulnerability Analysis

This vulnerability resides in the Server: Optimizer component of Oracle MySQL Server. The Optimizer is responsible for query planning and execution path determination, making it a critical component for database performance and stability. The vulnerability is classified under CWE-770 (Allocation of Resources Without Limits or Throttling), indicating that the root cause involves improper resource management within the query optimization process.

An attacker with low-level database privileges can craft specific queries or operations that trigger resource exhaustion or improper handling within the Optimizer component. This can lead to a complete hang or crash of the MySQL Server instance, denying service to all legitimate users and applications.

Root Cause

The vulnerability stems from CWE-770: Allocation of Resources Without Limits or Throttling. The MySQL Server Optimizer fails to properly limit or throttle resource allocation during certain operations, allowing an authenticated attacker to consume excessive resources or trigger conditions that cause the server to become unresponsive or crash.

This type of vulnerability in query optimizers typically occurs when processing complex or malformed queries that exploit algorithmic inefficiencies or boundary conditions in the optimization logic.

Attack Vector

The attack vector is network-based and requires low privileges to execute. An attacker must have valid credentials to authenticate to the MySQL Server, but only minimal permissions are needed to exploit this vulnerability. The attack can be conducted over multiple protocols supported by MySQL, including the standard MySQL protocol and potentially X Protocol.

The exploitation does not require user interaction and can be performed remotely, making it particularly dangerous in environments where MySQL servers are exposed to untrusted networks or where database credentials may have been compromised.

Detection Methods for CVE-2025-21500

Indicators of Compromise

Unexpected MySQL Server crashes or hangs, particularly following execution of complex queries
Abnormal resource consumption (CPU, memory) by the MySQL Server process
Error logs showing optimizer-related failures or resource exhaustion messages
Repeated connection failures from legitimate applications due to server unresponsiveness

Detection Strategies

Monitor MySQL Server error logs for optimizer-related errors and crash reports
Implement query logging to identify unusual or potentially malicious query patterns
Set up alerting for MySQL Server availability and response time degradation
Use process monitoring to detect abnormal resource consumption patterns

Monitoring Recommendations

Enable the MySQL Performance Schema to track query execution and resource usage
Configure slow query logging with appropriate thresholds to capture problematic queries
Implement database activity monitoring (DAM) solutions to detect anomalous access patterns
Set up high-availability monitoring to quickly detect and respond to service disruptions

How to Mitigate CVE-2025-21500

Immediate Actions Required

Review and update MySQL Server to patched versions as specified in Oracle's January 2025 Critical Patch Update
Audit database user privileges and remove unnecessary access to minimize attack surface
Implement network segmentation to limit MySQL Server exposure to trusted networks only
Review firewall rules to ensure MySQL ports are not exposed to untrusted networks

Patch Information

Oracle has released patches addressing this vulnerability as part of their January 2025 Critical Patch Update. Administrators should consult the Oracle Critical Patch Update January 2025 for specific patch details and upgrade instructions. Additionally, users of MySQL Server in NetApp environments should review the NetApp Security Advisory NTAP-20250131-0004 for product-specific guidance.

Upgrading to the following versions or later is recommended:

MySQL Server 8.0.41 or later for the 8.0.x branch
MySQL Server 8.4.4 or later for the 8.4.x branch
MySQL Server 9.1.1 or later for the 9.x branch

Workarounds

Implement strict query execution time limits using max_execution_time to prevent long-running queries from exhausting resources
Apply principle of least privilege to all database accounts, restricting access to only necessary operations
Use connection pooling with limits to prevent excessive concurrent connections from a single source
Consider implementing a database firewall or query analyzer to block suspicious query patterns

bash

# Configuration example - Resource limits in my.cnf
[mysqld]
# Set maximum query execution time (in milliseconds)
max_execution_time=30000

# Limit maximum concurrent connections
max_connections=150

# Set connection timeout values
wait_timeout=600
interactive_timeout=600

# Limit optimizer search depth to reduce complexity
optimizer_search_depth=10