CVE-2004-0836 in MySQL
Summary
by MITRE
Buffer overflow in the mysql_real_connect function in MySQL 4.x before 4.0.21, and 3.x before 3.23.49, allows remote DNS servers to cause a denial of service and possibly execute arbitrary code via a DNS response with a large address length (h_length).
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Analysis
by VulDB Data Team • 07/07/2025
The vulnerability described in CVE-2004-0836 represents a critical buffer overflow flaw within the MySQL database management system that affects versions prior to 4.0.21 and 3.23.49. This issue specifically targets the mysql_real_connect function which is responsible for establishing connections to MySQL servers. The vulnerability arises from insufficient input validation when processing DNS responses during the connection establishment process, creating a potential attack vector that could be exploited by malicious actors controlling remote DNS servers.
The technical flaw occurs when MySQL processes DNS responses containing unusually large address length fields, causing a buffer overflow condition in the mysql_real_connect function. This buffer overflow manifests when the system attempts to store DNS address information in a fixed-size buffer without proper bounds checking. The vulnerability is particularly dangerous because it can be triggered through DNS responses rather than direct network packets, making it more difficult to detect and prevent. The buffer overflow condition can result in program termination, memory corruption, and potentially arbitrary code execution depending on the specific memory layout and system configuration. This type of vulnerability falls under CWE-121, which describes stack-based buffer overflow conditions that occur when insufficient bounds checking is performed on buffer operations.
The operational impact of this vulnerability extends beyond simple denial of service scenarios to potentially enable remote code execution attacks. Attackers controlling malicious DNS servers can craft specially crafted responses that trigger the buffer overflow, causing MySQL processes to crash or potentially allowing attackers to inject and execute malicious code with the privileges of the MySQL service account. This creates a significant risk for database servers that rely on DNS resolution for connection establishment, particularly in environments where DNS security is not properly enforced. The vulnerability affects both MySQL 3.x and 4.x versions, representing a widespread issue that would impact numerous legacy database installations across various organizations.
Mitigation strategies for this vulnerability include immediate patching of affected MySQL versions to the recommended secure releases, implementing DNS security measures such as DNSSEC validation, and configuring network firewalls to restrict DNS query traffic to trusted DNS servers. Organizations should also consider implementing network segmentation to limit access to database servers and establish monitoring for unusual DNS traffic patterns that might indicate exploitation attempts. The ATT&CK framework categorizes this vulnerability under the T1210 technique for exploitation of remote services, while the CWE classification of 121 indicates this is a classic stack buffer overflow that requires proper bounds checking and input validation. System administrators should also implement regular vulnerability assessments and maintain up-to-date patch management procedures to prevent similar issues from affecting their database infrastructure.