CVE-2023-21911: Oracle MySQL Server InnoDB DoS Vulnerability

CVE-2023-21911 Overview

CVE-2023-21911 is a Denial of Service 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 via multiple protocols to compromise MySQL Server, resulting in the ability to cause a hang or frequently repeatable crash of the MySQL Server.

Critical Impact

Successful exploitation enables complete denial of service against MySQL Server through unauthorized crash or hang conditions, affecting availability for all connected applications and services.

Affected Products

• Oracle MySQL Server 8.0.32 and prior versions
• Fedora 37, 38, and 39
• NetApp Active IQ Unified Manager (VMware vSphere and Windows)
• NetApp OnCommand Insight
• NetApp OnCommand Workflow Automation
• NetApp SnapCenter

Discovery Timeline

• April 18, 2023 - CVE-2023-21911 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2023-21911

Vulnerability Analysis

This vulnerability resides in the InnoDB storage engine, which is the default transactional storage engine for MySQL Server. The flaw is easily exploitable and requires an attacker to have high privileges (such as administrative database access) combined with network connectivity to the MySQL Server instance.

The vulnerability specifically impacts the availability of the MySQL Server without affecting confidentiality or integrity. When exploited, the attack can cause the server to enter a hung state or trigger a frequently repeatable crash, effectively taking the database offline. This represents a complete denial of service condition that can disrupt all applications and services relying on the affected MySQL instance.

Given that InnoDB is responsible for handling critical database operations including transaction management, row-level locking, and crash recovery, any instability in this component has severe operational implications for enterprise environments.

Root Cause

The root cause relates to improper handling within the InnoDB storage engine that can be triggered by a privileged user through network protocols. While Oracle has not disclosed specific technical details about the vulnerable code path, the vulnerability appears to involve conditions that can be triggered remotely to destabilize the InnoDB engine, leading to server crashes or hangs.

Attack Vector

The attack requires:

1. Network access to the MySQL Server through supported protocols (MySQL protocol, X Protocol)
2. High-level privileges on the target MySQL instance (administrative or similarly elevated access)
3. Ability to execute specific operations that trigger the vulnerable condition in InnoDB

An authenticated attacker with administrative credentials can exploit this vulnerability remotely without any user interaction. The attack can be repeated to maintain a persistent denial of service condition, preventing legitimate users and applications from accessing the database.

Detection Methods for CVE-2023-21911

Indicators of Compromise

• Unexpected MySQL Server crashes or service restarts without clear operational cause
• Frequent "InnoDB" related error messages in MySQL error logs preceding server hangs
• Database connection timeouts and failures reported by applications
• MySQL server processes consuming excessive resources before becoming unresponsive

Detection Strategies

• Monitor MySQL error logs for InnoDB-related crash signatures and repeated restart patterns
• Implement database activity monitoring to detect unusual administrative operations from privileged accounts
• Configure alerting for MySQL service availability and unexpected process terminations
• Review authentication logs for suspicious privileged access patterns from unusual network sources

Monitoring Recommendations

• Enable MySQL performance schema and audit logging to capture administrative operations
• Implement real-time monitoring of MySQL process health and automatic service restart detection
• Deploy network-level monitoring to detect anomalous connection patterns to MySQL ports (3306, 33060)
• Establish baseline metrics for InnoDB buffer pool and transaction behavior to identify deviation patterns

How to Mitigate CVE-2023-21911

Immediate Actions Required

• Upgrade MySQL Server to version 8.0.33 or later which contains the security fix from Oracle
• Review and restrict high-privilege database accounts to only necessary personnel
• Implement network segmentation to limit MySQL Server exposure to trusted networks only
• Enable MySQL audit logging to track privileged operations

Patch Information

Oracle has addressed this vulnerability in the April 2023 Critical Patch Update (CPU). Administrators should apply the patch as soon as possible by upgrading to MySQL Server version 8.0.33 or later. The security advisory is available at the Oracle Security Alerts page.

Additional vendor patches are available:

• Fedora Package Announcements for Fedora 37, 38, and 39
• NetApp Security Advisory NTAP-20230427-0007 for affected NetApp products

Workarounds

• Restrict network access to MySQL Server using firewall rules to allow only trusted IP ranges
• Implement strict principle of least privilege for all MySQL user accounts, minimizing administrative access
• Deploy a database proxy or connection pooler to add an additional layer of access control
• Enable MySQL connection limits to prevent connection exhaustion during potential attack scenarios

# Configuration example - Restrict MySQL network access and enforce connection limits
# Add to my.cnf or my.ini configuration file

[mysqld]
# Bind to specific interface instead of all interfaces
bind-address = 127.0.0.1

# Limit maximum connections to prevent resource exhaustion
max_connections = 100

# Enable general query log for monitoring (use cautiously in production)
general_log = 1
general_log_file = /var/log/mysql/general.log

# Enable error logging for crash detection
log_error = /var/log/mysql/error.log
log_error_verbosity = 3