CVE-2026-22009: Oracle MySQL Server DOS Vulnerability

CVE-2026-22009 Overview

CVE-2026-22009 is a Denial of Service vulnerability in the MySQL Server product of Oracle MySQL, specifically affecting the Server: Optimizer component. This vulnerability allows a low-privileged attacker with network access to cause a complete denial of service condition, resulting in hangs or frequently repeatable crashes of the MySQL Server.

The vulnerability is classified as easily exploitable, meaning attackers can trigger it without sophisticated techniques or complex attack chains. The impact is purely on availability—there is no confidentiality or integrity breach associated with this vulnerability.

Critical Impact

Successful exploitation enables attackers to cause complete denial of service of MySQL Server through network-accessible protocols, potentially disrupting critical database operations and dependent applications.

Affected Products

• Oracle MySQL Server versions 8.0.0 through 8.0.45
• Oracle MySQL Server versions 8.4.0 through 8.4.8
• Oracle MySQL Server versions 9.0.0 through 9.6.0

Discovery Timeline

• 2026-04-21 - CVE-2026-22009 published to NVD
• 2026-04-23 - Last updated in NVD database

Technical Details for CVE-2026-22009

Vulnerability Analysis

This vulnerability resides in the MySQL Server Optimizer component, which is responsible for query execution planning and optimization. The Optimizer analyzes SQL queries and determines the most efficient execution path, making it a critical component that processes user-supplied input in the form of SQL queries.

The vulnerability is categorized under CWE-400 (Uncontrolled Resource Consumption), indicating that the issue involves improper handling of resource allocation during query optimization. When specific query patterns are submitted to the server, the Optimizer can enter a state that leads to excessive resource consumption, ultimately causing the server to hang or crash.

The attack can be executed via multiple network protocols supported by MySQL, including the standard MySQL protocol on port 3306, and potentially through other interfaces such as X Protocol. The low privilege requirement means any authenticated user with basic database access can potentially trigger this vulnerability.

Root Cause

The root cause of CVE-2026-22009 lies in the Server: Optimizer component's handling of certain query optimization scenarios. The vulnerability stems from uncontrolled resource consumption (CWE-400), where the optimizer fails to properly limit resource usage when processing specially crafted queries.

When the optimizer encounters specific query structures or optimization paths, it can enter a loop or allocate excessive resources without proper bounds checking. This leads to resource exhaustion that manifests as server hangs or crashes. The optimizer's complexity in handling various query patterns and execution plan calculations creates opportunities for such resource exhaustion conditions.

Attack Vector

The attack vector for CVE-2026-22009 is network-based, requiring only low-privilege access to the MySQL server. An attacker needs:

1. Network connectivity to the target MySQL Server via supported protocols
2. Valid authentication credentials with minimal privileges (any database user)
3. Ability to execute SQL queries against the server

The attacker submits specially crafted SQL queries that trigger the vulnerable code path in the Optimizer component. These queries are designed to cause the optimizer to consume excessive resources during the query planning phase, before actual query execution begins.

The vulnerability can be triggered by:

• Constructing complex queries with specific join patterns
• Using certain subquery structures that stress the optimizer
• Creating query conditions that force expensive optimization calculations

Since legitimate database users may inadvertently trigger this vulnerability, organizations should monitor for unusual query patterns and server resource usage.

Detection Methods for CVE-2026-22009

Indicators of Compromise

• Unexpected MySQL Server process crashes or hangs correlated with specific query execution
• Elevated CPU utilization by MySQL processes during query optimization phases
• Repeated server restarts without apparent infrastructure issues
• Error logs showing optimizer-related failures or resource exhaustion messages
• Database connection timeouts affecting multiple applications simultaneously

Detection Strategies

• Monitor MySQL error logs for optimizer-related crashes, segmentation faults, or abnormal termination signals
• Implement query auditing to identify unusual or complex query patterns submitted by users
• Set up alerting on MySQL process state changes and unexpected restarts
• Analyze slow query logs for queries that never complete or timeout during optimization
• Deploy database activity monitoring solutions to track query submission patterns

Monitoring Recommendations

• Enable MySQL performance schema monitoring for optimizer metrics and resource usage
• Configure automated alerting for MySQL service availability and response time degradation
• Implement connection pooling health checks to detect server unresponsiveness
• Set up centralized logging for MySQL error logs with real-time analysis capabilities
• Monitor system-level metrics (CPU, memory) for the MySQL process to detect resource exhaustion patterns

How to Mitigate CVE-2026-22009

Immediate Actions Required

• Apply the Oracle Critical Patch Update for April 2026 as soon as possible
• Review and restrict database user privileges to minimum required access levels
• Implement query timeout settings to limit resource consumption by individual queries
• Enable connection rate limiting to reduce potential for rapid exploitation attempts
• Consider implementing a database firewall or proxy to filter potentially malicious queries

Patch Information

Oracle has addressed this vulnerability in the April 2026 Critical Patch Update. The official security advisory is available at the Oracle Critical Patch Update Advisory.

Organizations should upgrade to the following patched versions:

• MySQL Server 8.0.46 or later for the 8.0.x branch
• MySQL Server 8.4.9 or later for the 8.4.x branch
• MySQL Server 9.6.1 or later for the 9.x branch

Before applying patches in production environments, test the updates in a staging environment to verify application compatibility.

Workarounds

• Implement strict query complexity limits using the max_execution_time system variable to prevent long-running operations
• Restrict optimizer features using optimizer_switch settings to disable potentially problematic optimization paths
• Use connection pooling with aggressive timeout settings to automatically terminate stalled connections
• Implement application-level query validation to reject overly complex queries before they reach the database
• Consider deploying MySQL in a high-availability configuration to minimize downtime impact from crashes

# Configuration example
# MySQL configuration recommendations for mitigating CVE-2026-22009
# Add to my.cnf or my.ini under [mysqld] section

# Limit query execution time (in milliseconds)
max_execution_time=30000

# Limit optimizer resource usage
optimizer_search_depth=10

# Set resource limits for optimizer
range_optimizer_max_mem_size=8388608

# Enable additional logging for troubleshooting
log_error_verbosity=3
slow_query_log=ON
long_query_time=5