CVE-2025-21523: Oracle MySQL Server DoS Vulnerability

CVE-2025-21523 Overview

CVE-2025-21523 is a denial of service vulnerability in the MySQL Server product of Oracle MySQL, specifically affecting the InnoDB storage engine component. This easily exploitable vulnerability allows a high-privileged attacker with network access via multiple protocols to compromise MySQL Server availability. Successful exploitation results in the unauthorized ability to cause a hang or frequently repeatable crash of MySQL Server, leading to complete denial of service.

Critical Impact

High-privileged attackers can cause complete denial of service by triggering a hang or repeatable crash of MySQL Server through the InnoDB component, disrupting database availability for all connected applications and services.

Affected Products

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

Discovery Timeline

• 2025-01-21 - CVE-2025-21523 published to NVD
• 2025-11-03 - Last updated in NVD database

Technical Details for CVE-2025-21523

Vulnerability Analysis

This vulnerability resides in the InnoDB storage engine, which is the default and most commonly used storage engine in MySQL. The weakness is classified under CWE-732 (Incorrect Permission Assignment for Critical Resource), indicating that the vulnerability stems from improper permission handling within the InnoDB component.

The vulnerability is exploitable over the network through multiple protocols, though it requires the attacker to possess high privileges (such as administrative database access). Despite the high privilege requirement, the attack complexity is low, meaning once an attacker has the necessary privileges, exploitation is straightforward and does not require user interaction.

The impact is strictly limited to availability—there is no compromise of data confidentiality or integrity. However, the availability impact is severe, allowing attackers to cause complete denial of service through either a persistent hang condition or a repeatable crash of the MySQL Server process.

Root Cause

The root cause of CVE-2025-21523 is attributed to incorrect permission assignment for critical resources within the InnoDB storage engine (CWE-732). This improper permission handling allows privileged users to trigger conditions that should be restricted, ultimately leading to resource exhaustion or crash conditions in the database server.

Attack Vector

The attack vector is network-based and can be leveraged through multiple database protocols supported by MySQL. An attacker with high-level privileges (such as a database administrator or user with elevated permissions) can send specially crafted requests that trigger the vulnerability in the InnoDB component. The attack requires no user interaction and affects only the vulnerable MySQL Server instance without propagating to other systems.

The attack scenario typically involves:

1. Attacker obtains or possesses high-privileged database credentials
2. Attacker connects to the MySQL Server over the network
3. Attacker issues specific operations targeting the InnoDB storage engine
4. MySQL Server enters a hang state or crashes, denying service to legitimate users

Detection Methods for CVE-2025-21523

Indicators of Compromise

• Unexpected MySQL Server crashes or process terminations, particularly those involving InnoDB operations
• Repeated hang conditions in the MySQL Server requiring manual intervention or automatic restart
• Unusual database connection patterns from privileged accounts preceding service disruptions
• MySQL error logs showing InnoDB-related errors or assertion failures

Detection Strategies

• Monitor MySQL Server process stability and uptime metrics for unexpected restarts or hang conditions
• Implement audit logging for privileged database operations, particularly those affecting InnoDB tables
• Configure alerting on MySQL crash logs and InnoDB-specific error messages
• Track authentication patterns for administrative database accounts to identify unauthorized access

Monitoring Recommendations

• Enable MySQL Enterprise Audit or equivalent logging solutions to capture privileged user activity
• Configure database monitoring tools to alert on MySQL Server availability drops or restart events
• Implement network monitoring to detect unusual connection patterns to MySQL ports from unexpected sources
• Review MySQL error logs regularly for signs of InnoDB instability or crash conditions

How to Mitigate CVE-2025-21523

Immediate Actions Required

• Apply the Oracle Critical Patch Update from January 2025 to all affected MySQL Server installations
• Review and restrict high-privilege database account access to only necessary personnel
• Implement network segmentation to limit MySQL Server exposure to trusted networks only
• Enable comprehensive logging to detect potential exploitation attempts

Patch Information

Oracle has released patches addressing this vulnerability in the January 2025 Critical Patch Update. Organizations should upgrade to the following patched versions:

• MySQL Server versions newer than 8.0.40 for the 8.0.x branch
• MySQL Server versions newer than 8.4.3 for the 8.4.x branch
• MySQL Server versions newer than 9.1.0 for the 9.x branch

Detailed patch information and download links are available in the Oracle Critical Patch Update Advisory. Additionally, NetApp has released a related security advisory for affected NetApp products, available at the NetApp Security Advisory.

Workarounds

• Restrict network access to MySQL Server to only trusted IP addresses and networks using firewall rules
• Implement the principle of least privilege by limiting the number of users with high-privilege database access
• Deploy MySQL in a segmented network environment isolated from untrusted networks
• Configure MySQL to bind only to internal network interfaces where possible

# Configuration example - Restrict MySQL network binding
# Edit my.cnf or my.ini configuration file

[mysqld]
# Bind MySQL to specific internal IP only
bind-address = 192.168.1.100

# Disable external network access if not required
# skip-networking = 1

# Enable general query logging for audit purposes
general_log = 1
general_log_file = /var/log/mysql/mysql-general.log