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A 9.8 severity vulnerability in Control Web Panel, previously known as CentOS Web Panel, allows an attacker to remotely execute arbitrary shell commands through a very simple mechanism. Although readily patched, security organizations are reporting it is under active exploit.

The unauthenticated remote code execution vulnerability affecting Control Web Panel (CWP) was discovered by Numan Türle of Gais Cyber Security and patched in version 0.9.8.1147, released on October 25. The vulnerability remained undisclosed until the beginning of 2023 to ensure CWP users had enough time to patch their systems.

According to Türle, the vulnerability allows an attacker to run arbitrary Bash commands by sending a maliciously crafted payload to the login endpoint. For example, you could send a POST HTTP message including the string $(whoami) in a URL query parameter to have the Linux shell command whoami executed when the request payload is written to log.

The vulnerability appears to be the result of missing user input validation, which should always be applied to prevent command injection, coupled with the direct use of shell redirection to append a string to a file. At source code level, the vulnerability manifests itself with the use of double quotes in the appending command, which leads to the possibility of command substitution, as seen in the above example. The use of single quotes would have prevented the most trivial attack schemes, yet it would have not prevented all of them in the first place. It fact, it appears that offloading the execution of such a simple task as appending to file to the shell was hardly a justified choice in terms of security.

Türle publicly disclosed the vulnerability on January 3 2023, additionally posting a video showing how easy it is to exploit. It took only a couple of days for attacks attempting to exploit the vulnerability to be detected by GreyNoise, which additionally provided the figure of five distinct IP addresses that were originating them.

Control Web Panel is a Linux server administration software that specifically target enterprise Linux distros. While its popularity is not in the top tier, it is used by over 35k servers worldwide. All organizations using it should ensure they are running version 0.9.8.1147 or higher.