CVE-2023-21913 Overview
CVE-2023-21913 is a Denial of Service vulnerability in the MySQL Server product of Oracle MySQL, specifically affecting the Server: Optimizer component. This vulnerability allows a high-privileged attacker with network access via multiple protocols to compromise MySQL Server, resulting in an unauthorized ability to cause a hang or frequently repeatable crash of the MySQL Server.
Critical Impact
Successful exploitation of this vulnerability can result in a complete Denial of Service (DoS) of MySQL Server, causing significant availability impacts to database operations and dependent applications.
Affected Products
- Oracle MySQL Server version 8.0.31 and prior
- Oracle MySQL Server deployments accessible via network protocols
- Systems using MySQL Server with the Optimizer component enabled
Discovery Timeline
- April 18, 2023 - CVE-2023-21913 published to NVD
- November 21, 2024 - Last updated in NVD database
Technical Details for CVE-2023-21913
Vulnerability Analysis
This vulnerability resides in the Server: Optimizer component of Oracle MySQL Server. The Optimizer is a critical component responsible for determining the most efficient execution plan for SQL queries. When exploited, the vulnerability allows an authenticated attacker with high privileges to trigger conditions that cause the MySQL Server to hang or crash repeatedly.
The attack requires network access and can be executed via multiple protocols supported by MySQL Server. While the vulnerability requires high privileges to exploit, the ease of exploitation combined with the severe availability impact makes it a significant concern for database administrators managing MySQL deployments.
Root Cause
The vulnerability stems from improper handling within the MySQL Server Optimizer component. While Oracle has not disclosed specific technical details about the root cause, the vulnerability classification indicates an issue in how the Optimizer processes certain inputs or query patterns, leading to resource exhaustion or unhandled error conditions that result in server instability.
Attack Vector
The attack vector for CVE-2023-21913 involves network-based exploitation through protocols supported by MySQL Server. An attacker with high-level privileges (such as database administrator credentials) can send specially crafted requests or queries that trigger the vulnerability in the Optimizer component.
The vulnerability is characterized by:
- Network accessibility: The attack can be conducted remotely over the network
- High privilege requirement: Attacker must possess elevated database privileges
- No user interaction: Exploitation does not require any action from other users
- Availability impact: Complete denial of service is achievable
Due to the nature of this vulnerability and responsible disclosure practices, specific exploitation techniques are not being detailed. The vulnerability mechanism involves triggering abnormal behavior in the query optimizer that leads to server crashes or hangs. For technical details, refer to the Oracle Security Alert.
Detection Methods for CVE-2023-21913
Indicators of Compromise
- Unexpected MySQL Server crashes or restarts without apparent system resource issues
- Repeated server hangs during query optimization phases
- Anomalous query patterns from privileged database accounts
- Error logs showing optimizer-related failures or exceptions
Detection Strategies
- Monitor MySQL error logs for unexpected crashes or hangs related to query optimization
- Implement database activity monitoring (DAM) to detect unusual query patterns from privileged accounts
- Configure alerting for MySQL Server availability issues and unexpected restarts
- Review audit logs for privileged account activity that precedes server instability
Monitoring Recommendations
- Enable comprehensive MySQL Server logging including error logs and slow query logs
- Implement real-time monitoring of MySQL Server availability and performance metrics
- Set up automated alerts for repeated server crashes or extended hang conditions
- Monitor network traffic to MySQL ports for anomalous connection patterns from privileged sources
How to Mitigate CVE-2023-21913
Immediate Actions Required
- Upgrade MySQL Server to a version newer than 8.0.31 that contains the security fix
- Review and restrict high-privilege database account access to trusted administrators only
- Implement network segmentation to limit access to MySQL Server from untrusted networks
- Enable enhanced logging to detect potential exploitation attempts
Patch Information
Oracle has addressed this vulnerability in their April 2023 Critical Patch Update. Administrators should upgrade to MySQL Server versions released after 8.0.31 to remediate this vulnerability. The official security advisory is available at the Oracle Security Alert CPUAPR2023.
Additional vendor advisories:
Workarounds
- Restrict network access to MySQL Server using firewall rules to allow only trusted IP addresses
- Implement additional authentication controls for privileged database accounts
- Monitor and audit all privileged database account activity
- Consider implementing a database activity monitoring solution for real-time threat detection
# Example: Restrict MySQL network access using firewall rules (iptables)
# Allow MySQL connections only from trusted internal network
iptables -A INPUT -p tcp --dport 3306 -s 10.0.0.0/8 -j ACCEPT
iptables -A INPUT -p tcp --dport 3306 -j DROP
# Review privileged MySQL accounts
mysql -u root -p -e "SELECT user, host FROM mysql.user WHERE Super_priv='Y';"
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
