CVE-2009-4030 in MySQL
Summary
by MITRE
MySQL 5.1.x before 5.1.41 allows local users to bypass certain privilege checks by calling CREATE TABLE on a MyISAM table with modified (1) DATA DIRECTORY or (2) INDEX DIRECTORY arguments that are originally associated with pathnames without symlinks, and that can point to tables created at a future time at which a pathname is modified to contain a symlink to a subdirectory of the MySQL data home directory, related to incorrect calculation of the mysql_unpacked_real_data_home value. NOTE: this vulnerability exists because of an incomplete fix for CVE-2008-4098 and CVE-2008-2079.
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Analysis
by VulDB Data Team • 08/28/2021
This vulnerability in MySQL 5.1.x versions prior to 5.1.41 represents a significant privilege escalation issue that exploits improper path resolution during table creation operations. The flaw specifically manifests when local users execute CREATE TABLE statements on MyISAM tables with modified DATA DIRECTORY or INDEX DIRECTORY arguments that initially reference pathnames devoid of symbolic links. The vulnerability arises from an incorrect calculation of the mysql_unpacked_real_data_home value, which creates a path traversal condition that bypasses normal privilege checks. This issue is particularly concerning because it allows attackers to manipulate table creation processes to gain unauthorized access to MySQL data structures that should otherwise be restricted.
The technical implementation of this vulnerability involves a sophisticated manipulation of filesystem path resolution within the MySQL storage engine. When a user creates a table with specific directory arguments, the system calculates the real data home path incorrectly, failing to properly validate or sanitize the path components. This miscalculation occurs because the mysql_unpacked_real_data_home value does not account for potential symbolic link modifications that may occur between the initial table creation request and the actual table creation process. The vulnerability specifically leverages the fact that pathnames without symlinks can later be modified to contain symlinks pointing to subdirectories within the MySQL data home directory, creating a window where privilege checks can be bypassed.
Operationally, this vulnerability presents a severe risk to database security as it enables local users to potentially access or modify database tables that they should not have permission to access. The impact extends beyond simple privilege escalation to potentially allow data theft, modification, or corruption of database contents. Attackers can exploit this flaw by creating tables with carefully crafted directory arguments, then modifying the filesystem paths to include symbolic links that point to restricted areas of the database structure. This creates a scenario where legitimate privilege checks are circumvented, allowing unauthorized access to database resources that should be protected by standard access controls.
The vulnerability represents an incomplete fix for previously identified issues CVE-2008-4098 and CVE-2008-2079, indicating that the remediation process failed to address all potential attack vectors within the path resolution mechanism. This incomplete remediation demonstrates a common challenge in security patching where fixes may address surface-level symptoms without resolving underlying architectural flaws. Organizations running affected MySQL versions face significant risk as this vulnerability can be exploited by any local user with access to the database server, potentially leading to complete database compromise. The vulnerability aligns with CWE-22 (Improper Limitation of a Pathname to a Restricted Directory) and CWE-73 (External Control of File Name or Path) categories, and could be mapped to ATT&CK techniques involving privilege escalation and persistence through file system manipulation.
Mitigation strategies should focus on immediate patching to MySQL 5.1.41 or later versions that properly address the path resolution calculation issue. System administrators should also implement comprehensive monitoring of table creation operations and directory modifications within MySQL data directories. Additional protective measures include restricting local user access to database servers where possible, implementing proper file system permissions, and conducting regular security audits of MySQL configuration files and directory structures. Organizations should also consider implementing database activity monitoring solutions that can detect anomalous CREATE TABLE operations with unusual directory arguments, providing early warning of potential exploitation attempts.