CVE-2026-21952: MySQL Server Parser DoS Vulnerability

CVE-2026-21952 Overview

CVE-2026-21952 is a Denial of Service vulnerability affecting the MySQL Server product of Oracle MySQL, specifically within the Server: Parser 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 with administrative privileges to completely disrupt MySQL Server availability through easily exploitable attack vectors.

Affected Products

• MySQL Server versions 9.0.0 through 9.5.0

Discovery Timeline

• January 20, 2026 - CVE-2026-21952 published to NVD
• January 21, 2026 - Last updated in NVD database

Technical Details for CVE-2026-21952

Vulnerability Analysis

This vulnerability resides in the Parser component of MySQL Server, which is responsible for interpreting and processing SQL statements. The flaw is classified under CWE-400 (Uncontrolled Resource Consumption), indicating that the parser fails to properly manage resources when processing certain inputs.

The vulnerability is network-accessible and can be exploited through multiple protocols supported by MySQL Server. While the attack requires high privileges (such as administrative access), the exploitation complexity is low, meaning no special conditions or circumstances are required beyond having authenticated access with elevated permissions.

The impact is limited to availability—there is no confidentiality or integrity breach associated with this vulnerability. However, the availability impact is complete, allowing an attacker to induce a persistent crash or hang state in the MySQL Server instance.

Root Cause

The root cause stems from improper resource management within the SQL parser component. When processing specially crafted SQL statements or queries, the parser enters a state that leads to uncontrolled resource consumption, ultimately resulting in service disruption. This aligns with CWE-400 (Uncontrolled Resource Consumption), where the application does not properly restrict the amount of resources that are consumed by an actor.

Attack Vector

The attack vector is network-based, allowing exploitation from any network location that can reach the MySQL Server. The attacker must possess high-level privileges on the MySQL instance to execute the malicious queries. Once authenticated with appropriate privileges, the attacker can submit malformed or specially crafted SQL statements that trigger the parser vulnerability, causing the server to hang or crash repeatedly.

The exploitation does not require user interaction and affects only the vulnerable MySQL Server instance without impacting other components in the environment (unchanged scope).

Detection Methods for CVE-2026-21952

Indicators of Compromise

• Unexpected MySQL Server crashes or hangs without apparent cause
• Unusual SQL query patterns from privileged accounts in MySQL query logs
• Resource exhaustion alerts related to the MySQL process
• Repeated service restarts or availability incidents on MySQL instances

Detection Strategies

• Monitor MySQL error logs for parser-related crashes or abnormal terminations
• Implement query auditing for privileged database accounts to detect anomalous activity
• Deploy database activity monitoring (DAM) solutions to track administrative SQL operations
• Configure alerts for MySQL service interruptions or unexpected restarts

Monitoring Recommendations

• Enable MySQL General Query Log for privileged accounts during investigation periods
• Set up automated health checks to detect MySQL Server unresponsiveness
• Monitor system resource utilization (CPU, memory) for MySQL processes
• Review authentication logs for unusual privileged account activity patterns

How to Mitigate CVE-2026-21952

Immediate Actions Required

• Apply the latest Oracle Critical Patch Update (CPU) January 2026 to affected MySQL Server installations
• 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 and monitoring for privileged database operations

Patch Information

Oracle has addressed this vulnerability in the Oracle Security Alert January 2026. Organizations running MySQL Server versions 9.0.0 through 9.5.0 should upgrade to the latest patched version as soon as possible.

The patch is available through Oracle's standard security update channels. Customers with active support contracts can download the update from the Oracle Software Delivery Cloud or My Oracle Support portal.

Workarounds

• Restrict network access to MySQL Server using firewall rules to limit exposure
• Enforce least-privilege access principles for database accounts
• Implement connection throttling or rate limiting for database connections
• Consider temporarily disabling remote access for high-privileged accounts until patching is complete

# Example: Restrict MySQL access using firewall rules
# Allow MySQL connections only from trusted application servers
sudo iptables -A INPUT -p tcp --dport 3306 -s 10.0.1.0/24 -j ACCEPT
sudo iptables -A INPUT -p tcp --dport 3306 -j DROP

# Review privileged users with SUPER or ALL PRIVILEGES
mysql -e "SELECT user, host FROM mysql.user WHERE Super_priv='Y';"