CVE-2026-21937 Overview
A denial of service vulnerability exists in the MySQL Server product of Oracle MySQL, specifically within the Server: DDL (Data Definition Language) component. This vulnerability allows a high-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.
Critical Impact
Successful exploitation enables attackers to cause complete availability loss of MySQL Server instances through network-based attacks, potentially disrupting critical database operations and dependent applications.
Affected Products
- MySQL Server versions 8.0.0 through 8.0.44
- MySQL Server versions 8.4.0 through 8.4.7
- MySQL Server versions 9.0.0 through 9.5.0
Discovery Timeline
- 2026-01-20 - CVE-2026-21937 published to NVD
- 2026-01-20 - Last updated in NVD database
Technical Details for CVE-2026-21937
Vulnerability Analysis
This vulnerability resides in the DDL (Data Definition Language) component of MySQL Server, which handles database schema operations such as CREATE, ALTER, DROP, and TRUNCATE statements. The flaw is characterized as easily exploitable, requiring only high-privileged access to trigger the vulnerable condition.
The impact is limited to availability, with no confidentiality or integrity concerns. When exploited, the vulnerability causes the MySQL Server to either hang completely or enter a state where it crashes repeatedly, effectively rendering the database service unavailable to legitimate users and applications.
Root Cause
The vulnerability stems from improper handling within the DDL processing logic of MySQL Server. While specific technical details have not been publicly disclosed, the nature of the vulnerability suggests a resource management or state handling issue within the DDL component that can be triggered through crafted DDL operations by an authenticated, high-privileged user.
Attack Vector
The attack requires network access to the MySQL Server through multiple supported protocols. An attacker must possess high-level privileges (such as administrative or DBA-level access) to execute the malicious operations. The attack does not require user interaction and has unchanged scope, meaning the vulnerability impact is contained within the MySQL Server component itself.
The exploitation scenario involves a privileged attacker sending specially crafted DDL statements to the vulnerable MySQL Server instance, triggering the denial of service condition. This could be exploited by:
- Malicious database administrators
- Compromised privileged accounts
- Attackers who have escalated privileges through other means
Detection Methods for CVE-2026-21937
Indicators of Compromise
- Unexpected MySQL Server crashes or hangs coinciding with DDL operations
- Abnormal patterns of DDL statement execution from privileged accounts
- Repeated service restarts of MySQL Server without apparent cause
- Error logs showing DDL-related failures or resource exhaustion
Detection Strategies
- Monitor MySQL Server error logs for crash dumps related to DDL operations
- Implement audit logging for all DDL statements executed by privileged users
- Set up alerting for MySQL Server process terminations and restarts
- Track connection patterns from accounts with high privileges
Monitoring Recommendations
- Enable MySQL Enterprise Audit or equivalent logging for DDL operations
- Configure process monitoring to detect MySQL Server crashes
- Implement database activity monitoring for privileged account actions
- Establish baseline metrics for DDL operation frequency and duration
How to Mitigate CVE-2026-21937
Immediate Actions Required
- Review and verify the access rights of all high-privileged MySQL accounts
- Implement principle of least privilege for database administrator accounts
- Enable comprehensive audit logging for DDL operations
- Plan upgrade to patched MySQL Server versions as soon as available
Patch Information
Oracle has addressed this vulnerability in the January 2026 Critical Patch Update. Administrators should consult the Oracle Security Alert January 2026 for specific patch information and upgrade guidance. Affected organizations should prioritize upgrading to the latest patched versions of MySQL Server:
- For MySQL 8.0.x: Upgrade to version 8.0.45 or later
- For MySQL 8.4.x: Upgrade to version 8.4.8 or later
- For MySQL 9.x: Upgrade to version 9.5.1 or later
Workarounds
- Restrict network access to MySQL Server to trusted hosts and networks only
- Review and minimize the number of accounts with high privileges
- Implement network segmentation to isolate database servers
- Monitor privileged account activity for anomalous DDL operations
# Configuration example - Restrict MySQL network access
# In my.cnf or my.ini configuration file
[mysqld]
# Bind to specific trusted interface only
bind-address = 10.0.1.50
# Enable audit logging for DDL operations
audit_log_policy = ALL
audit_log_format = JSON
# Limit connections from specific hosts via host-based access controls
# Use GRANT statements with specific host restrictions for privileged accounts
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
