tnftp "savefile" Arbitrary Command Execution

This Metasploit module exploits an arbitrary command execution vulnerability in tnftp’s handling of the resolved output filename – called “savefile” in the source – from a requested resource. If tnftp is executed without the -o command-line option, it will resolve the output filename from the last component of the requested resource. If the output filename begins with a “|” character, tnftp will pass the fetched resource’s output to the command directly following the “|” character through the use of the popen() function.
Source: tnftp "savefile" Arbitrary Command Execution