After seeing this arbitrary command execution vulnerability in Ubiquiti equipment, discovered by SEC Consult, I was intrigued. In that bug, code that would have been secure on a more recent version of PHP was rendered vulnerable because of the ancient PHP version used (2.0.1, which is nearly 20 years old). I wanted to see what other bugs might be caused by PHP that works in unexpected ways.
My friend owns a “NanoBeam AC” running firmware WA_v8.0.1, so I downloaded that firmware from Ubiquiti’s website and unpacked it with binwalk. I found a bunch of PHP scripts, a custom patched PHP 2.0.1 binary, and a custom patched Lighttpd server which handles session management and serves the files.