CVE-2007-4844 in Unreal Commander
Summary
by MITRE
X-Diesel Unreal Commander 0.92 build 565 and 573 does not properly react to an FTP server s behavior after sending a "CWD /" command, which allows remote FTP servers to cause a denial of service (infinite loop) by (1) repeatedly sending a 550 error response, or (2) sending a 550 error response and then disconnecting.
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Analysis
by VulDB Data Team • 10/30/2017
The vulnerability identified as CVE-2007-4844 affects X-Diesel Unreal Commander version 0.92 build 565 and 573, representing a critical denial of service weakness in FTP client software. This flaw manifests when the application fails to properly handle the response behavior of remote FTP servers following the execution of a "CWD /" command, which is a standard directory change operation in FTP protocol communication. The issue stems from inadequate state management and error handling mechanisms within the client's FTP implementation, creating a scenario where malicious or misconfigured FTP servers can exploit the application's response processing logic to trigger unintended behavior.
The technical implementation of this vulnerability involves the client application's failure to establish proper boundaries for handling FTP server responses, particularly those containing 550 error codes which indicate "file not found" or "directory not accessible" conditions. When the Unreal Commander application sends a "CWD /" command to navigate to the root directory and receives repeated 550 responses, or experiences a 550 response followed by immediate disconnection, the client's processing loop becomes trapped in an infinite cycle. This occurs because the application lacks proper timeout mechanisms or response validation logic to break out of repeated error states, causing the software to consume excessive system resources and become unresponsive.
From an operational perspective, this vulnerability presents a significant risk to systems utilizing Unreal Commander for FTP operations, as it can be exploited by remote attackers to cause persistent service disruption without requiring authentication or advanced privileges. The infinite loop condition essentially renders the application unusable until manual intervention occurs, potentially affecting users who rely on the software for file management tasks. This type of denial of service attack can be particularly damaging in environments where the affected software serves as a critical component of file transfer operations, as it can impact productivity and potentially serve as a stepping stone for more sophisticated attacks.
The vulnerability aligns with CWE-835, which describes the weakness of an infinite loop or infinite recursion in software implementations, and demonstrates how improper error handling can lead to system instability. Additionally, this flaw relates to ATT&CK technique T1499.004, which covers network disruption through denial of service attacks. The root cause lies in the application's lack of robust input validation and state management, where the software fails to implement proper defensive programming practices such as maximum retry limits, connection timeouts, or proper error state transitions. Organizations should implement immediate mitigations including updating to patched versions of Unreal Commander, implementing network-level protections to restrict FTP server access, and establishing monitoring for unusual connection patterns that may indicate exploitation attempts.
The broader implications of this vulnerability highlight the importance of defensive programming practices in networked applications, particularly those handling protocol communications where external parties control the input behavior. Proper implementation of timeout mechanisms, error code validation, and state machine management would have prevented the infinite loop condition, demonstrating how basic software engineering principles can prevent significant security issues. This case study serves as a reminder of the critical need for comprehensive error handling in client applications that interact with potentially malicious or unreliable network services, as the absence of such safeguards can lead to complete service disruption with minimal attacker effort.