thumbnail 5 mins left

HackTheBox Notes - Curling (ft. Anger)

5 min read from infosec on 2019-04-01

Continuing from last time where I just post my notes, today is Curling. Also note that today is the first of April, and my April fools joke is that this is not an April fools joke… or is it? I jest of course, these notes are already enough of a joke.

Nmap Scan

Starting Nmap 7.70 ( https://nmap.org ) at 2018-11-05 09:58 AEDT
Nmap scan report for
Host is up (0.49s latency).
Not shown: 998 closed ports
22/tcp open  ssh     OpenSSH 7.6p1 Ubuntu 4 (Ubuntu Linux; protocol 2.0)
| ssh-hostkey:
|   2048 8a:d1:69:b4:90:20:3e:a7:b6:54:01:eb:68:30:3a:ca (RSA)
|   256 9f:0b:c2:b2:0b:ad:8f:a1:4e:0b:f6:33:79:ef:fb:43 (ECDSA)
|_  256 c1:2a:35:44:30:0c:5b:56:6a:3f:a5:cc:64:66:d9:a9 (ED25519)
80/tcp open  http    Apache httpd 2.4.29 ((Ubuntu))
|_http-generator: Joomla! - Open Source Content Management
|_http-server-header: Apache/2.4.29 (Ubuntu)
|_http-title: Home
Service Info: OS: Linux; CPE: cpe:/o:linux:linux_kernel

Service detection performed. Please report any incorrect results at https://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 23.14 seconds

Joomla! Site

  • Has upload button at bottom of all pages
  • shows version is 3.8.8. Released May 22 2018
  • Page /secret.txt displays Q3VybGluZzIwMTgh. Tried this as password on /administrator with user admin but nope.
    • It’s actually base64. Decodes into Curling2018!. Still doesn’t work with admin
    • Found username Floris in one of the articles. Worked with Curling2018!
  • Looked at this to upload a PHP shell from this
    • Created new file in templates hello.php and put shellcode there
    • Run nc -lvpn <port_number>
    • Go to
    • Got shell as user www-data

PHP Reverse Shell

  • Can’t get user.txt because we don’t have permissions for ~/floris but we can view another file password_backup[1]. It’s a hexdump for something…
  • This list of file signatures tells us the file is a bz2 file because it has the signature 42 5A 68 at the start
  • Went to /var/www/html/bin because the user has write permissions there
  • Copied /home/floris/password_backup
  • Reversed the hexdump back to a bz2 file with xxd -r password_backup password_backup.bz2
  • Decompressed the file bzip2 -d password_backup.bz2
  • Contains the string
l[passwordrBZh91AY&SY6@@Pt t"dhhOPIS@68ET>P@#I |3x(*N&Hk1x"{]B@6m

What is this

  • Did a file on it password_backup: gzip compressed data, was "password", last modified: Tue May 22 19:16:20 2018, from Unix Oh it’s zipped again

  • Added .gz as a file extension and unzipped it

$ gunzip password_backup.gz
$ cat password_backup
BZh91AY&SY6@@Pt t"dhhOPIS@68ET>P@#I |3x(*N&Hk1x"{]B@6


  • Checked file again
$ file password_backup
password_backup: bzip2 compressed data, block size = 900k

This is getting really annoying

  • OK
$ mv password_backup password_backup.bz2
$ bzip2 -d password_backup.bz2
$ cat password_backup
password.txt0000644000000000000000000000002313301066143012147 0ustar  rootroot5d<wdCbdZu)|hChXll

Fucks sake

$ type password_backup
password_backup: POSIX tar archive (GNU)


  • Maybe this will be the last time…
$ mv password_backup password_backup.tar
$ tar -xvf password_backup.tar


$ cat password.txt

SSH Server


  • Logged in floris@ with password 5d<wdCbdZu)|hChXll
  • Get user cat user.txt. What a fucking pain

  • Folder ~/admin-area has files input and report
    • Whenever one is edited it is reverted back a while later by something
    • ls -al shows it’s being edited every minute. I’m, pretty sure we’re dealing with cron here
  • Had a guess that a cron job was calling curl with a url from the file input and redirecting the result to report
    • Changed the url in input from to file:///home/floris/user.txt
    • Wait for the start of the next minute and report now has the user hash. So yep, i’m right
  • Changed url to file:///root/root.txt (probably should have done this as the first test)
  • And now we wait…
floris@curling:~/admin-area$ date
Mon Nov  5 06:52:01 UTC 2018
floris@curling:~/admin-area$ ls -al
total 16
drwxr-x--- 2 root   floris 4096 May 22 19:04 .
drwxr-xr-x 7 floris floris 4096 Nov  5 06:51 ..
-rw-rw---- 1 root   floris   25 Nov  5 06:52 input
-rw-rw---- 1 root   floris   33 Nov  5 06:52 report
floris@curling:~/admin-area$ cat report

There must have been a way to find out that cron was using curl instead of pure guesswork, but oh well.


[1]: 00000000: 425a 6839 3141 5926 5359 819b bb48 0000 BZh91AY&SY...H.. 00000010: 17ff fffc 41cf 05f9 5029 6176 61cc 3a34 ....A...P)ava.:4 00000020: 4edc cccc 6e11 5400 23ab 4025 f802 1960 N...n.T.#.@%...` 00000030: 2018 0ca0 0092 1c7a 8340 0000 0000 0000 ......z.@...... 00000040: 0680 6988 3468 6469 89a6 d439 ea68 c800 ..i.4hdi...9.h.. 00000050: 000f 51a0 0064 681a 069e a190 0000 0034 ..Q..dh........4 00000060: 6900 0781 3501 6e18 c2d7 8c98 874a 13a0 i...5.n......J.. 00000070: 0868 ae19 c02a b0c1 7d79 2ec2 3c7e 9d78 .h...*..}y..<~.x 00000080: f53e 0809 f073 5654 c27a 4886 dfa2 e931 .>...sVT.zH....1 00000090: c856 921b 1221 3385 6046 a2dd c173 0d22 .V...!3.`F...s." 000000a0: b996 6ed4 0cdb 8737 6a3a 58ea 6411 5290 ..n....7j:X.d.R. 000000b0: ad6b b12f 0813 8120 8205 a5f5 2970 c503 .k./... ....)p.. 000000c0: 37db ab3b e000 ef85 f439 a414 8850 1843 7..;.....9...P.C 000000d0: 8259 be50 0986 1e48 42d5 13ea 1c2a 098c .Y.P...HB....*.. 000000e0: 8a47 ab1d 20a7 5540 72ff 1772 4538 5090 .G.. .U@r..rE8P. 000000f0: 819b bb48 ...H