CVE-2004-1848 in WS_FTP Server
Summary
by MITRE
Ipswitch WS_FTP Server 4.0.2 allows remote attackers to cause a denial of service (disk consumption) and bypass file size restrictions via a REST command with a large size argument, followed by a STOR of a smaller file.
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Analysis
by VulDB Data Team • 06/27/2019
The vulnerability identified as CVE-2004-1848 affects Ipswitch WS_FTP Server version 4.0.2, presenting a significant security flaw that enables remote attackers to exploit the service through a specific sequence of commands. This vulnerability operates within the context of file transfer protocols where the server fails to properly validate file size parameters during the transfer process, creating an exploitable condition that can lead to both denial of service and privilege escalation through file size restriction bypass.
The technical implementation of this vulnerability stems from the server's improper handling of the REST (restart) command followed by the STOR (store) command in the File Transfer Protocol. When an attacker sends a REST command with an excessively large size argument, the server allocates disk space accordingly, preparing for what it believes will be a large file transfer. Subsequently, when the attacker sends a STOR command with a much smaller file, the server maintains the large allocated space reservation while storing only the small file, resulting in significant disk space wastage. This flaw exists because the server does not validate that the size argument in the REST command corresponds to the actual file size that will be transferred, creating a mismatch between allocated resources and actual usage.
The operational impact of this vulnerability extends beyond simple resource exhaustion, as it provides attackers with a method to consume disk space rapidly and potentially render the server unusable. The denial of service aspect occurs because the server's disk space becomes consumed by the oversized file reservations, preventing legitimate users from uploading files or causing the server to crash entirely. Additionally, the ability to bypass file size restrictions represents a privilege escalation vector, as attackers can circumvent configured limits that would normally prevent large file transfers, potentially enabling them to upload malicious files or exhaust storage resources more efficiently than normal operations would allow.
The vulnerability aligns with CWE-129, which addresses improper validation of array indices and buffer overflows, as the server fails to validate input parameters before allocating system resources. From an ATT&CK framework perspective, this vulnerability maps to T1499.004, specifically the technique of "File System Wipe" through resource exhaustion, and T1078.002, which covers "Valid Accounts: Default Accounts" when considering that such exploits often leverage default server configurations. The exploitation pattern follows T1210, "Exploitation of Remote Services," as it requires remote access to the FTP server and leverages specific command sequences to achieve the desired outcome.
Mitigation strategies should focus on implementing proper input validation and resource management within the FTP server configuration. Administrators should apply the latest security patches provided by Ipswitch, which would address the flawed command handling logic. Additionally, implementing strict file size limits and monitoring disk usage can help detect and prevent exploitation attempts. Network segmentation and access control measures should be employed to limit exposure, while regular security audits should verify that the server configuration properly validates all input parameters before resource allocation occurs. The vulnerability demonstrates the importance of proper resource management in network services and the necessity of validating all user-supplied parameters to prevent resource exhaustion attacks that can lead to complete service disruption.