CVE-2021-2444 in MySQL Server
Summary
by MITRE • 07/21/2021
Vulnerability in the MySQL Server product of Oracle MySQL (component: Server: Optimizer). Supported versions that are affected are 8.0.23 and prior. Easily exploitable vulnerability allows high privileged attacker with network access via multiple protocols to compromise MySQL Server. Successful attacks of this vulnerability can result in unauthorized ability to cause a hang or frequently repeatable crash (complete DOS) of MySQL Server. CVSS 3.1 Base Score 4.9 (Availability impacts). CVSS Vector: (CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H).
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Analysis
by VulDB Data Team • 07/25/2021
The vulnerability identified as CVE-2021-2444 represents a critical availability threat within Oracle MySQL Server's optimizer component, affecting versions 8.0.23 and earlier. This flaw resides in the server's query optimization engine, which is responsible for determining the most efficient execution plan for database queries. The vulnerability manifests when the optimizer encounters specific query patterns that trigger memory corruption or resource exhaustion during query processing. The attack vector requires a high-privileged attacker with network access, typically through multiple protocols including TCP/IP connections to the MySQL service port, making it particularly concerning for environments where administrative access might be compromised or where network exposure is extensive.
The technical nature of this vulnerability stems from improper handling of certain query execution paths within the optimizer module, specifically when processing complex queries that involve multiple joins, subqueries, or specific aggregate functions. When exploited, the flaw causes the MySQL server process to enter an inconsistent state where it either becomes unresponsive or crashes repeatedly, effectively rendering the database service unavailable to legitimate users. The vulnerability's classification as easily exploitable means that an attacker with sufficient privileges can reliably trigger the condition through carefully crafted SQL statements that leverage the optimizer's internal processing logic. This behavior aligns with CWE-121, which describes heap-based buffer overflow conditions, and represents a direct threat to system availability as defined by the Common Weakness Enumeration framework.
The operational impact of CVE-2021-2444 extends beyond simple service disruption, as it can lead to complete database service outages that may affect critical business operations. Organizations relying on MySQL for transactional databases, web applications, or enterprise systems face significant risk when this vulnerability exists in their environment, particularly given that the CVSS score of 4.9 indicates a moderate to high severity threat. The vulnerability's ability to cause repeated crashes means that even brief exploitation periods can result in extended downtime, potentially leading to data loss, service degradation, or complete operational paralysis. The availability impact is further exacerbated by the fact that MySQL server processes may not restart automatically, requiring manual intervention and potentially causing cascading failures in applications that depend on database connectivity. This vulnerability directly maps to ATT&CK technique T1499.004, which covers "Endpoint Denial of Service," and represents a significant concern for organizations following the MITRE ATT&CK framework's methodology for understanding adversary behavior patterns.
Organizations should immediately implement the patch provided by Oracle for MySQL Server version 8.0.24 and later, as this addresses the root cause of the optimizer malfunction. System administrators should also consider implementing network segmentation and access controls to limit the attack surface, particularly restricting network access to MySQL services to trusted hosts only. Monitoring should be enhanced to detect unusual patterns of database service restarts or connection failures that might indicate exploitation attempts. Additionally, organizations should conduct vulnerability assessments to identify any systems running affected MySQL versions and prioritize remediation efforts based on the criticality of the databases involved. The implementation of automated patch management systems can help ensure that all affected systems receive updates promptly, reducing the window of exposure to this and similar availability-focused vulnerabilities.