Synopsis
While developing a Nessus plugin, Tenable found that CVE-2018-14933 was insufficiently patched. NUUO originally tried to fix CVE-2018-14933 by enforcing authentication on upgrade_handle.php. They also introduced the following logic in an attempt to filter out uploaddir variables with system commands:
$uploaddir = $_GET['uploaddir'];
if(strpos($uploaddir, ';') !== false)
{
die('[1]Not a valid path.');
}
However, the above logic doesn't account for other techniques, such as using logical operators, to inject shell commands. If a remote authenticated attacker set uploaddir to "|| whoami" then it would bypass the filter and the "whoami" command would be executed as part of the following logic:
$current_dir = system('cat '.PHP_CINF_PATH.'| grep \'upload_tmp_dir\'');
$tmp_upload_dir = 'upload_tmp_dir='.$uploaddir;
$cmd = "sed -i 's/".str_replace('/', '\/', $current_dir)."/".str_replace('/', '\/', $tmp_upload_dir)."/g' ".PHP_CINF_PATH;
system($cmd);
A full proof of concept can be found in our GitHub repository.
Solution
Upgrade to firmware version 3.10.0 or later.Additional References
https://www.nuuo.com/DownloadDetail.php?id=0118https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2018-14933
https://github.com/tenable/poc/tree/master/nuuo/nvrmini2/cve_2018_15716
Disclosure Timeline
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