BASH Level 5

Table of Contents

Guess the listening port!

Problem

#!/bin/bash

x=$(shuf -i 1024-65500 -n 1)
echo "Guess the listening port"
input=$(nc -lp $x)
echo "That was easy right? :)"
cat flag.txt

Solution

Terminal #1

It just popped out the flag as soon as I tried to connect to the port and break the connection!

level5@74faccee6de9:~$ sudo -u root ./portforce.sh
Guess the listening port
That was easy right? :)
auctf{n3tc@_purt_$can}

Terminal #2

Use to find what ports are listening

  • port is in HEX.
level5@74faccee6de9:/proc/5934/net$ cat tcp
  sl  local_address rem_address   st tx_queue rx_queue tr tm->when retrnsmt   uid  timeout inode
   0: 00000000:2793 00000000:0000 0A 00000000:00000000 00:00000000 00000000     0        0 397645058 1 0000000000000000 100 0 0 10 0
   1: 00000000:0016 00000000:0000 0A 00000000:00000000 00:00000000 00000000     0        0 377103420 1 0000000000000000 100 0 0 10 0
   2: 00000000:35FB 00000000:0000 0A 00000000:00000000 00:00000000 00000000     0        0 393051118 1 0000000000000000 100 0 0 10 0

Terminal #3

Use to decide which port is mine.

0x2793 equals with 10131

level5@74faccee6de9:/tmp$ nc 127.0.0.1 10131
111111
1
1
1
^C
level5@74faccee6de9:/tmp$
Nemo Xiong avatar
Nemo Xiong
ex-Cybersecurity Executor, now a student in Unimelb
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