CVE-1999-0999 in SQL Server
Summary
by MITRE
Microsoft SQL 7.0 server allows a remote attacker to cause a denial of service via a malformed TDS packet.
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Analysis
by VulDB Data Team • 01/19/2025
Microsoft SQL Server 7.0 presents a critical vulnerability that enables remote attackers to execute denial of service attacks through the manipulation of Tabular Data Stream TDS packets. This flaw resides in the server's packet parsing mechanism where insufficient validation occurs during the processing of incoming TDS protocol communications. The vulnerability specifically targets the server's handling of malformed TDS packets which can trigger unexpected behavior in the database engine's network protocol stack. When an attacker crafts and transmits specially crafted TDS packets that violate the expected packet format or contain invalid data structures, the SQL Server 7.0 service becomes vulnerable to crash conditions or resource exhaustion scenarios. This issue falls under the category of input validation failures and can be classified as CWE-129, representing improper validation of input boundaries. The attack vector requires network access to the SQL Server instance and can be executed without authentication, making it particularly dangerous in environments where the database server is accessible from untrusted networks. The operational impact of this vulnerability extends beyond simple service disruption as it can lead to complete database availability loss, potentially affecting business-critical applications that depend on the SQL Server infrastructure. According to ATT&CK framework, this vulnerability maps to T1499.004 which covers network denial of service attacks, and T1566.001 which involves phishing attacks through network protocols. The vulnerability affects systems running Microsoft SQL Server 7.0 where the TDS protocol is actively listening on network ports, typically port 1433 or other custom configured ports. The flaw represents a fundamental issue in the protocol implementation where the server does not adequately sanitize incoming packet data before processing, creating an opportunity for malformed data to cause the service to terminate unexpectedly or enter a non-responsive state. This vulnerability was particularly significant in the context of SQL Server 7.0 as it represented one of the early instances where protocol-level flaws could be exploited to compromise service availability. The lack of proper input validation in the TDS packet handling code means that even seemingly benign malformed packets can trigger buffer overflows or memory corruption conditions within the database engine. Organizations running SQL Server 7.0 should implement immediate mitigations including network segmentation, firewall rules restricting access to SQL Server ports, and application-layer filtering to prevent malformed TDS packets from reaching the database engine. The vulnerability demonstrates the importance of robust protocol validation and input sanitization in database server implementations, highlighting that even protocol-level flaws can result in complete service disruption. Security professionals should note that this vulnerability type represents a common pattern in database server implementations where network protocol handling lacks sufficient validation mechanisms, making it a critical area for defensive measures. The impact of this vulnerability extends to all applications and services that rely on the affected SQL Server instances, potentially causing cascading failures throughout enterprise infrastructure where database availability is critical for business operations. Mitigation strategies should include implementing network-level controls to filter suspicious TDS traffic, applying security patches when available, and monitoring for unusual network patterns that might indicate exploitation attempts. The vulnerability also underscores the need for comprehensive security testing of protocol implementations, particularly in database servers where network accessibility increases the attack surface. Organizations should consider upgrading to supported versions of SQL Server that have addressed this and similar protocol-level vulnerabilities, as SQL Server 7.0 reached end-of-life and no longer receives security updates. The flaw represents a classic example of how protocol-level vulnerabilities can be exploited to achieve denial of service outcomes, emphasizing the importance of proper input validation and robust error handling in network services. This vulnerability type specifically impacts the reliability and availability of database services and can be leveraged by attackers to disrupt business operations through service unavailability. The technical nature of this vulnerability requires that security teams implement both network-level and application-level protections to defend against potential exploitation attempts.