CVE-2025-21555: Oracle MySQL Server DOS Vulnerability

CVE-2025-21555 Overview

CVE-2025-21555 is an authorization bypass vulnerability in the MySQL Server product of Oracle MySQL, specifically affecting the InnoDB storage engine component. This vulnerability allows a high-privileged attacker with network access to compromise MySQL Server through multiple protocols. Successful exploitation can result in denial of service conditions through system hangs or repeatable crashes, as well as unauthorized modification of MySQL Server accessible data.

Critical Impact

This vulnerability enables complete denial of service through server crashes and unauthorized data modification capabilities, potentially disrupting database availability and data integrity for affected MySQL deployments.

Affected Products

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

Discovery Timeline

• 2025-01-21 - CVE-2025-21555 published to NVD
• 2025-11-03 - Last updated in NVD database

Technical Details for CVE-2025-21555

Vulnerability Analysis

This vulnerability resides in the InnoDB storage engine, which is the default transactional storage engine for MySQL. The flaw is classified under CWE-863 (Incorrect Authorization), indicating that the vulnerability stems from improper authorization checks within the InnoDB component.

The vulnerability is easily exploitable, requiring network access but limited to attackers who already possess high privileges on the MySQL Server. The attack can be conducted through multiple network protocols supported by MySQL, including the standard MySQL protocol and potentially administrative interfaces.

When successfully exploited, this vulnerability impacts both system availability and data integrity. The availability impact is significant, allowing attackers to induce complete denial of service through system hangs or frequently repeatable crashes. Additionally, attackers gain unauthorized ability to update, insert, or delete some MySQL Server accessible data, though confidentiality is not affected.

Root Cause

The root cause is an incorrect authorization vulnerability (CWE-863) within the InnoDB storage engine. This type of flaw occurs when authorization checks fail to properly validate whether a user has the necessary permissions to perform certain operations. In this case, the InnoDB component does not adequately enforce authorization boundaries, allowing privileged users to perform actions that should be restricted or that cause unintended system behavior.

Attack Vector

The attack vector is network-based, requiring the attacker to have high-level privileges on the MySQL Server. The exploitation path involves:

1. An authenticated attacker with administrative or high-privilege database access connects to the MySQL Server via network protocols
2. The attacker sends specially crafted requests targeting the InnoDB storage engine
3. Due to improper authorization checks, these requests bypass intended restrictions
4. The exploitation results in either a complete denial of service (server hang or crash) or unauthorized data modification

The vulnerability does not require user interaction and operates within the context of the vulnerable MySQL Server without changing scope to affect other components.

Detection Methods for CVE-2025-21555

Indicators of Compromise

• Unexpected MySQL Server crashes or hangs, particularly those coinciding with administrative user activity
• Anomalous database modifications or unauthorized INSERT, UPDATE, or DELETE operations in MySQL logs
• Repeated server restarts or service interruptions without apparent cause
• Unusual network connections from privileged accounts to the MySQL Server

Detection Strategies

• Monitor MySQL error logs for crash dumps and InnoDB-specific error messages indicating abnormal termination
• Implement database activity monitoring to track privileged user operations and identify anomalous query patterns
• Configure audit logging for all administrative actions on MySQL Server instances
• Deploy network monitoring to detect unusual patterns in MySQL protocol traffic from privileged accounts

Monitoring Recommendations

• Enable MySQL general query log and slow query log for forensic analysis capabilities
• Configure alerting for MySQL Server process crashes or unexpected restarts
• Implement real-time monitoring of InnoDB status variables for signs of corruption or instability
• Review privileged user access patterns and establish baselines for normal administrative activity

How to Mitigate CVE-2025-21555

Immediate Actions Required

• Apply the Oracle Critical Patch Update (CPU) January 2025 to all affected MySQL Server installations immediately
• Review and restrict high-privilege account access to only essential personnel
• Implement network segmentation to limit MySQL Server exposure to untrusted networks
• Enable comprehensive audit logging to detect potential exploitation attempts

Patch Information

Oracle has addressed this vulnerability in the Oracle Critical Patch Update January 2025. Organizations should upgrade to patched versions of MySQL Server:

• MySQL Server versions after 8.0.40
• MySQL Server versions after 8.4.3
• MySQL Server versions after 9.1.0

Additional security guidance is available in the NetApp Security Advisory NTAP-20250131-0004 for NetApp products that incorporate MySQL.

Workarounds

• Restrict network access to MySQL Server to only trusted IP addresses and networks using firewall rules
• Implement the principle of least privilege by reviewing and reducing high-privilege account permissions
• Consider placing MySQL Server behind a VPN or bastion host to limit exposure
• Enable MySQL connection limits and resource restrictions to mitigate potential DoS impact

# Configuration example - Restrict MySQL network access and enable logging
# In my.cnf or mysqld.cnf

[mysqld]
# Bind MySQL to specific interface
bind-address = 127.0.0.1

# Enable general query log for monitoring
general_log = 1
general_log_file = /var/log/mysql/general.log

# Enable audit logging (MySQL Enterprise)
# audit_log_file = /var/log/mysql/audit.log

# Limit connections per user
max_user_connections = 50