CVE-2008-3731 in Serv-U
Summary
by MITRE
Unspecified vulnerability in Serv-U File Server 7.0.0.1, and other versions before 7.2.0.1, allows remote authenticated users to cause a denial of service (daemon crash) via an SSH session with SFTP commands for directory creation and logging.
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Analysis
by VulDB Data Team • 08/16/2019
The vulnerability identified as CVE-2008-3731 represents a critical denial of service flaw within the Serv-U File Server software ecosystem. This issue affects versions prior to 7.2.0.1 and specifically targets the Secure Shell (SSH) implementation within the file server daemon. The vulnerability manifests when authenticated remote users exploit specific SFTP commands related to directory creation and logging operations, ultimately leading to complete daemon crashes that disrupt file sharing services for all connected users. The flaw demonstrates a fundamental weakness in input validation and resource management within the SSH subsystem, creating an avenue for malicious actors to intentionally destabilize the file server infrastructure.
From a technical perspective, the vulnerability stems from inadequate error handling mechanisms within the SFTP command processing pipeline. When authenticated users submit directory creation commands combined with specific logging parameters, the Serv-U daemon fails to properly validate or sanitize the input parameters before executing the underlying operations. This lack of proper input validation creates a condition where malformed or specially crafted SFTP commands can trigger memory corruption or resource exhaustion within the daemon process. The vulnerability aligns with CWE-129, which addresses improper validation of length of input buffers, and CWE-248, which covers exposure of an exception to external actors. The flaw operates at the application layer within the SSH protocol implementation, making it particularly dangerous as it requires only authentication credentials to exploit, not elevated privileges.
The operational impact of this vulnerability extends beyond simple service disruption, creating cascading effects that can severely compromise business continuity and data availability. When the daemon crashes, all active SFTP sessions are terminated abruptly, forcing users to re-authenticate and potentially lose unsaved work or ongoing file transfers. Network administrators face the challenge of maintaining service uptime while the vulnerability remains unpatched, as the denial of service can be executed repeatedly by authenticated users. The attack vector presents a significant risk to organizations relying on Serv-U for file sharing operations, particularly in environments where multiple users maintain authenticated access to the system. This vulnerability directly maps to the ATT&CK technique T1499.004, which involves network denial of service attacks, and T1566.002, covering spearphishing through social engineering, as the attack requires valid credentials to execute successfully.
Organizations should implement immediate mitigations while planning for comprehensive patching operations to address this vulnerability. The most effective immediate solution involves applying the vendor-supplied security patch that addresses the specific SFTP command processing flaw. System administrators should also consider implementing network-level restrictions that limit the number of concurrent SFTP sessions and monitor for unusual patterns of directory creation and logging commands. Additional defensive measures include configuring intrusion detection systems to identify suspicious SFTP command sequences and implementing stricter access controls that limit which users can perform directory creation operations. The vulnerability highlights the importance of maintaining current security patches and conducting regular vulnerability assessments of critical infrastructure components. Organizations should also consider implementing redundant file sharing solutions and establishing incident response procedures specifically designed to handle daemon crash scenarios. Regular security audits and penetration testing should be conducted to identify similar weaknesses in other network services and ensure comprehensive protection against similar exploitation vectors.