CVE-2018-20684 in WinSCP
Summary
by MITRE
In WinSCP before 5.14 beta, due to missing validation, the scp implementation would accept arbitrary files sent by the server, potentially overwriting unrelated files. This affects TSCPFileSystem::SCPSink in core/ScpFileSystem.cpp.
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Analysis
by VulDB Data Team • 06/26/2023
The vulnerability identified as CVE-2018-20684 represents a critical file system security flaw in WinSCP versions prior to 5.14 beta, specifically within the Secure Copy Protocol implementation. This issue manifests in the TSCPFileSystem::SCPSink function located in core/ScpFileSystem.cpp, where inadequate input validation allows malicious servers to manipulate file transfer operations. The flaw stems from insufficient verification of file paths and names during SCP protocol processing, creating a potential attack vector that could be exploited by remote adversaries controlling the server component of the transfer.
The technical nature of this vulnerability aligns with CWE-22, which describes improper limitation of a pathname to a restricted directory, commonly known as path traversal attacks. When a client receives file data from a server during SCP operations, the implementation fails to properly validate the destination paths, allowing attackers to specify arbitrary file locations that may overwrite existing files on the client system. This type of vulnerability is particularly dangerous because SCP is designed to provide secure file transfer capabilities, yet this flaw undermines the fundamental security assumptions of the protocol.
From an operational perspective, this vulnerability could enable attackers to execute unauthorized file modifications or even complete system compromise if they can control the server component of a transfer. The impact extends beyond simple file overwrites, as malicious actors could potentially overwrite critical system files, configuration data, or user documents. The vulnerability affects any WinSCP client that establishes connections with compromised servers, making it particularly concerning for organizations that maintain multiple client systems or use automated file transfer processes.
The security implications of CVE-2018-20684 align with several tactics described in the MITRE ATT&CK framework, particularly those related to privilege escalation and persistence. Attackers could leverage this vulnerability to establish backdoors or maintain access by overwriting legitimate files with malicious counterparts. Organizations using WinSCP for regular file transfers are at risk, especially in environments where server compromise is possible, as the vulnerability does not require authentication to exploit and can be triggered through normal file transfer operations. The remediation approach involves updating to WinSCP version 5.14 or later, where proper input validation has been implemented to prevent arbitrary file overwrites, and administrators should also review their file transfer processes to ensure they are not inadvertently exposing systems to compromised server environments.