CVE-2000-0855 in SunFTP
Summary
by MITRE
SunFTP build 9(1) allows remote attackers to cause a denial of service by connecting to the server and disconnecting before sending a newline.
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Analysis
by VulDB Data Team • 10/12/2025
The vulnerability identified as CVE-2000-0855 affects SunFTP build 9(1) and represents a classic denial of service flaw that exploits improper handling of connection termination sequences. This issue demonstrates a fundamental weakness in the FTP server's protocol implementation where the system fails to properly manage client disconnections that occur before the completion of standard command sequences. The vulnerability specifically targets the server's response to premature disconnections, creating a scenario where malicious actors can repeatedly establish connections and terminate them without sending the required newline character that typically signals the end of a command. This behavior can be exploited to consume server resources through connection management overhead, ultimately leading to service unavailability for legitimate users.
From a technical perspective, the flaw resides in the FTP server's inability to gracefully handle incomplete command sequences during the connection lifecycle. When a client connects to the SunFTP server and immediately disconnects without sending the terminating newline character, the server's internal state management becomes inconsistent. This particular implementation defect allows the server to maintain connection tracking information for these incomplete sessions, creating resource exhaustion conditions that can be amplified through repeated exploitation. The vulnerability operates at the protocol level and demonstrates poor error handling in the server's connection state machine, where the system fails to properly clean up resources associated with incomplete connection attempts. This issue falls under the broader category of resource exhaustion vulnerabilities and can be classified as a CWE-400 weakness related to unspecified resource management issues.
The operational impact of CVE-2000-0855 extends beyond simple service disruption to potentially affect system availability and performance across networked environments. An attacker can leverage this vulnerability to consume server memory and processing resources through repeated connection attempts, effectively creating a denial of service condition that impacts legitimate users' ability to access FTP services. The attack vector is particularly insidious because it requires minimal resources to execute and can be automated to create sustained service disruption. Network administrators may observe increased connection handling overhead and potential system instability as the server struggles to manage the accumulation of incomplete session states. This vulnerability also highlights the importance of proper protocol implementation and the need for robust error handling in server applications, particularly those handling network connections with complex state transitions.
Mitigation strategies for CVE-2000-0855 should focus on implementing proper connection state management and resource cleanup mechanisms within the FTP server implementation. System administrators should consider applying vendor patches or upgrading to newer versions of SunFTP that address this specific vulnerability. Network-level mitigations can include implementing connection rate limiting and monitoring for unusual connection patterns that may indicate exploitation attempts. The implementation of proper timeout mechanisms and connection cleanup procedures helps prevent resource exhaustion by ensuring that incomplete connection states do not persist indefinitely. Additionally, security monitoring should include detection of rapid connection and disconnection sequences that match the exploit pattern described in the vulnerability. Organizations should also consider implementing network segmentation and access controls to limit exposure to this type of denial of service attack, aligning with the principles of defense in depth as outlined in cybersecurity frameworks such as those referenced in the MITRE ATT&CK framework. The vulnerability serves as a reminder of the critical importance of proper protocol implementation and the need for comprehensive testing of edge cases in network service applications.