A recently disclosed maximum-severity security flaw impacting the Wing FTP Server has come under active exploitation in the wild, according to Huntress.
The vulnerability, tracked as CVE-2025-47812 (CVSS score: 10.0), is a case of improper handling of null (‘ ’) bytes in the server’s web interface, which allows for remote code execution. It has been addressed in version 7.4.4.
“The user and admin web interfaces mishandle ‘ ’ bytes, ultimately allowing injection of arbitrary Lua code into user session files,” according to an advisory for the flaw on CVE.org. “This can be used to execute arbitrary system commands with the privileges of the FTP service (root or SYSTEM by default).”
What makes it even more concerning is that the flaw can be exploited via anonymous FTP accounts. A comprehensive breakdown of the vulnerability entered the public domain towards the end of June 2025, courtesy of RCE Security researcher Julien Ahrens.
Cybersecurity company Huntress said it observed threat actors exploiting the flaw to download and execute malicious Lua files, conduct reconnaissance, and install remote monitoring and management software.
“CVE-2025-47812 stems from how null bytes are handled in the username parameter (specifically related to the loginok.html file, which handles the authentication process),” Huntress researchers said. “This can allow remote attackers to perform Lua injection after using the null byte in the username parameter.”
“By taking advantage of the null-byte injection, the adversary disrupts the anticipated input in the Lua file which stores these session characteristics.”
Evidence of active exploitation was first observed against a single customer on July 1, 2025, merely a day after details of the exploit were disclosed. Upon gaining access, the threat actors are said to have run enumeration and reconnaissance commands, created new users as a form of persistence, and dropped Lua files to drop an installer for ScreenConnect.
There is no evidence that the remote desktop software was actually installed, as the attack was detected and stopped before it could progress any further. It’s currently not clear who is behind the activity.
Data from Censys shows that there are 8,103 publicly-accessible devices running Wing FTP Server, out of which 5,004 have their web interface exposed. The majority of the instances are located in the U.S., China, Germany, the U.K., and India.
In light of active exploitation, it’s essential that users move quickly to apply the latest patches and update their Wing FTP Server versions of 7.4.4 or later.
