CVE-2009-4048 in XM Easy Personal FTP Server
Summary
by MITRE
Dxmsoft XM Easy Personal FTP Server 5.8.0 allows remote authenticated users to cause a denial of service (daemon outage) via an APPE command to one socket in conjunction with a DELE command to a second socket.
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Analysis
by VulDB Data Team • 10/14/2025
The vulnerability identified as CVE-2009-4048 affects Dxmsoft XM Easy Personal FTP Server version 5.8.0 and represents a denial of service flaw that can be exploited by authenticated remote attackers. This issue stems from improper handling of concurrent FTP commands across multiple socket connections, creating a condition where the server daemon becomes unresponsive and ultimately crashes. The vulnerability specifically manifests when an attacker sends an APPE command to one socket connection while simultaneously issuing a DELE command to a different socket connection within the same server instance.
The technical root cause of this vulnerability lies in the server's inadequate synchronization mechanisms and resource management when processing concurrent file operations. The APPE command is used to append data to a file while the DELE command removes files from the server's file system. When these commands are executed concurrently across different sockets, the server's internal state management fails to properly coordinate the operations, leading to a race condition that ultimately results in daemon termination. This flaw demonstrates poor implementation of concurrent access controls and lacks proper mutex or semaphore mechanisms to prevent conflicting operations on shared resources.
From an operational impact perspective, this vulnerability creates a significant risk for organizations relying on this FTP server implementation. The denial of service condition effectively renders the FTP service unavailable to legitimate users, potentially disrupting business operations that depend on file transfer capabilities. The attack requires only authenticated access, which means that any user with valid credentials can potentially exploit this vulnerability. This makes the flaw particularly dangerous in environments where FTP services are exposed to untrusted networks or where credential compromise is possible through other attack vectors. The impact extends beyond simple service disruption as it can affect data availability and business continuity.
The vulnerability aligns with CWE-362, which describes a race condition in concurrent programming where two or more threads or processes access shared resources concurrently and the final outcome depends on the timing of execution. Additionally, this issue relates to ATT&CK technique T1499.004, which covers the use of network denial of service attacks to disrupt services. The flaw can be classified as a daemon crash vulnerability that affects the availability aspect of the CIA triad. Organizations should consider implementing network segmentation to limit access to FTP services and ensure that only authorized users can establish connections. The recommended mitigation includes applying the vendor's official patch or upgrade to a version that addresses this concurrency issue. Alternatively, administrators should implement connection rate limiting and monitoring to detect anomalous command patterns that might indicate exploitation attempts. Regular security assessments and vulnerability scanning should include checks for this specific issue to prevent unauthorized exploitation and maintain service availability.