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 get_client_addr 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 get_client_addr 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
get_client_addr 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 poll_for_data retrieves
a few request parameters and loads the corresponding poller_item entries
from the database. If the action of a poller_item equals
POLLER_ACTION_SCRIPT_PHP, the function proc_open is used to execute a
PHP script. The attacker-controlled parameter $poller_id is retrieved via
the function get_nfilter_request_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 local_data_id,
where the action of the corresponding poller_item is set to
POLLER_ACTION_SCRIPT_PHP. Both of these ids (host_id and
local_data_id) can easily be bruteforced. The only requirement is that a
poller_item with an POLLER_ACTION_SCRIPT_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
POLLER_ACTION_SCRIPT_PHP (2) is configured. The authorization bypass
should be prevented by not allowing an attacker to make get_client_addr
(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.