CVE-2022-46169

Cacti is an open source platform which provides a robust and extensible operational monitoring and fault management framework for users. In affected versions a command injection vulnerability allows an unauthenticated user to execute arbitrary code on a server running Cacti, if a specific data source was selected for any monitored device. The vulnerability resides in the remote_agent.php file. This file can be accessed without authentication. This function retrieves the IP address of the client via getclientaddr and resolves this IP address to the corresponding hostname via gethostbyaddr. After this, it is verified that an entry within the poller table exists, where the hostname corresponds to the resolved hostname. If such an entry was found, the function returns true and the client is authorized. This authorization can be bypassed due to the implementation of the getclientaddr function. The function is defined in the file lib/functions.php and checks serval $_SERVER variables to determine the IP address of the client. The variables beginning with HTTP_ can be arbitrarily set by an attacker. Since there is a default entry in the poller table with the hostname of the server running Cacti, an attacker can bypass the authentication e.g. by providing the header Forwarded-For: <TARGETIP>. This way the function getclientaddr returns the IP address of the server running Cacti. The following call to gethostbyaddr will resolve this IP address to the hostname of the server, which will pass the poller hostname check because of the default entry. After the authorization of the remote_agent.php file is bypassed, an attacker can trigger different actions. One of these actions is called polldata. The called function pollfordata retrieves a few request parameters and loads the corresponding poller_item entries from the database. If the action of a poller_item equals POLLERACTIONSCRIPT_PHP, the function proc_open is used to execute a PHP script. The attacker-controlled parameter $poller_id is retrieved via the function getnfilterrequest_var, which allows arbitrary strings. This variable is later inserted into the string passed to proc_open, which leads to a command injection vulnerability. By e.g. providing the poller_id=;id the id command is executed. In order to reach the vulnerable call, the attacker must provide a host_id and localdataid, where the action of the corresponding poller_item is set to POLLERACTIONSCRIPT_PHP. Both of these ids (host_id and localdataid) can easily be bruteforced. The only requirement is that a poller_item with an POLLERACTIONSCRIPT_PHP action exists. This is very likely on a productive instance because this action is added by some predefined templates like Device - Uptime or Device - Polling Time.

This command injection vulnerability allows an unauthenticated user to execute arbitrary commands if a poller_item with the action type POLLERACTIONSCRIPT_PHP (2) is configured. The authorization bypass should be prevented by not allowing an attacker to make getclientaddr (file lib/functions.php) return an arbitrary IP address. This could be done by not honoring the HTTP_... $_SERVER variables. If these should be kept for compatibility reasons it should at least be prevented to fake the IP address of the server running Cacti. This vulnerability has been addressed in both the 1.2.x and 1.3.x release branches with 1.2.23 being the first release containing the patch.