CVE-2002-0509 in Oracle9i
Summary
by MITRE
Transparent Network Substrate (TNS) Listener in Oracle 9i 9.0.1.1 allows remote attackers to cause a denial of service (CPU consumption) via a single malformed TCP packet to port 1521.
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Analysis
by VulDB Data Team • 09/16/2025
The Transparent Network Substrate listener in Oracle 9i version 9.0.1.1 represents a critical vulnerability that enables remote attackers to execute denial of service attacks through carefully crafted network traffic. This vulnerability specifically targets the TNS listener component which serves as the primary communication interface for Oracle database services, operating on the standard port 1521. The flaw exploits a weakness in the listener's packet processing logic that fails to properly validate incoming TCP packets, creating a condition where a single malformed packet can trigger excessive CPU resource consumption. The vulnerability demonstrates the classic characteristics of a resource exhaustion attack pattern that aligns with attack techniques described in the MITRE ATT&CK framework under the resource exhaustion category.
The technical implementation of this vulnerability stems from insufficient input validation within the TNS listener's network protocol handling mechanism. When the listener receives a malformed TCP packet on port 1521, the parsing routine enters an infinite loop or consumes excessive computational resources during the validation process. This behavior creates a scenario where legitimate database connections cannot be processed while the system becomes overwhelmed with processing the malicious packet. The vulnerability affects the core listener functionality that manages all incoming database connection requests, making it particularly dangerous as it can render the entire database service unavailable to legitimate users. The flaw operates at the network protocol level and does not require authentication or specific privileges to exploit, making it a significant threat vector for attackers seeking to disrupt database operations.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise business continuity and data availability. Organizations relying on Oracle 9i databases for critical operations face the risk of extended downtime while the system consumes excessive CPU resources. The attack can be executed from any remote location with network access to port 1521, making it particularly challenging to defend against since traditional network segmentation may not prevent the attack. System administrators often cannot distinguish between legitimate high CPU usage and malicious activity caused by this vulnerability, leading to delayed response times. The vulnerability also impacts the overall network infrastructure as the excessive CPU consumption can affect other services running on the same system or network segment. This type of vulnerability is particularly concerning in environments where database availability is mission-critical and where attackers may use it as part of a broader attack strategy.
Mitigation strategies for this vulnerability require immediate action including applying the official Oracle patch releases that address the TNS listener validation issue. Organizations should also implement network-level controls such as firewall rules that restrict access to port 1521 from trusted networks only, and consider implementing intrusion detection systems to monitor for suspicious packet patterns. The vulnerability aligns with CWE-129 which describes improper validation of input boundaries, and represents a classic example of how protocol-level flaws can be exploited to consume system resources. Network administrators should also consider implementing rate limiting and connection tracking mechanisms to detect and prevent the exploitation of similar vulnerabilities. Regular security assessments and vulnerability scanning should be conducted to identify other potential weaknesses in the Oracle database infrastructure. The remediation process should include thorough testing of patches in non-production environments before deployment to ensure compatibility with existing database configurations and applications.