h4ck/revolabs-flx_uc_1000

revolabs flx UC1000

found this device in a conference room, found the IP from an unauthenticated menu on the dialer, which was accessible from the wireless 'Guest' network. it also has USB ports, so potentially available without network access.

story time

from the page that loaded when you first hit http://<device>, noticed app.js was being loaded.

in it, i found:

 sys.password:
  - defaultVal: "7386",
  - pattern: /^(\d{4,})$/,

so we can assume that there are only 9999 possibilities, which is definitely small enough to brute force.

there doesn't seem to be any protection/rate limiting - other than the CPU, so.. bf_login.rb

tools

name	description
bf_login.rb	brute forces the PIN on the web interface
generate_contacts.rb	generates potentially malicious contact files to be uploaded

bf_login.rb

key	value
single	./bf_login.rb 192.168.1.1
range	./bf_login.rb 192.168.1.*, will hit 1..254

attempts to connect to an HTTP endpoint, and then attempts to auth until the PIN is found:

• valid range is 0000 to 9999
• since possibly set by humans, prioritize progressive/related/repeating combinations

found PINs are output to a SQLite3 database, bflogin.db, and if scanning a host where PIN is already known, they immediately return.

generate_contacts.rb

key	value
usage	./generate_contacts.rb

builds potentially (as in untested) malicious contact files, attempting to exploit:

• too many contacts, currently 100k (2.9mb) (contacts-huge.csv)
• duplicate name/phone/ID contacts (contacts-duplicates.csv)

more testing and expansion to come.

functionality exposed via web interface

• change settings
  • screen brightness, timeout, enable/disable
  • LED colors, enable/disable
  • SIP settings
  • DHCP, NTP settings
  • name displayed
  • etc
• upgrade firmware - need to do more digging here
• restart device
• pull logs/configuration
  • SIP password is not included in exported config.xml

the same functionality, in a different interface is now available on the dialer as well as via HTTP. interestingly, many features/settings are exposed on the dialer, while all access over HTTP must be authenticated

further research

SIP password exposed

the SIP password is notably absent from configuration exports, and masked in the browser, but there are 2 avenues to recovering it anyway:

• once the PIN is known, viewing 'Options'->'SIP settings' from the physical device exposes the plaintext password
• the PIN is masked in the web interface, but only because the , and since the traffic is running over HTTP, sniffing web traffic while the page is loaded exposes the plaintext password

in a twist on the second issue mentioned above, if any other changes are made on the 'SIP Settings' page (like the display name), when 'Submit' is clicked, your browser will prompt you to save the password. standard saved password recovery tools will expose the plaintext password too

firmware digging

from Settings-> functionality, ps.txt confirmed that the machine is running a small Linux distribution. a quick check of the manufacturers website gave us a copy of the latest firmware 2.6.0.294

binwalking the uncompressed file:

$ binwalk FLX-UC-1500-2-6-0-294.bundle

DECIMAL       HEXADECIMAL     DESCRIPTION
--------------------------------------------------------------------------------
138364        0x21C7C         CRC32 polynomial table, little endian
266272        0x41020         uImage header, header size: 64 bytes, header CRC: 0x4A150CD3, created: 2016-03-11 22:03:35, image size: 1338940 bytes, Data Address: 0xC0008000, Entry Point: 0xC0008000, data CRC: 0x793D4693, OS: Linux, CPU: ARM, image type: OS Kernel Image, compression type: none, image name: "Linux-2.6.37+"
283460        0x45344         gzip compressed data, maximum compression, from Unix, last modified: 2016-03-11 22:03:34
1708064       0x1A1020        Squashfs filesystem, little endian, version 4.0, compression:gzip, size: 17871508 bytes, 1007 inodes, blocksize: 131072 bytes, created: 2016-03-11 22:17:40
19642065      0x12BB6D1       Zlib compressed data, best compression

of particular interest to us is 0x1A1020 Squashfs filesystem..:

# mkdir /squash/
# mount -o loop -t squashfs /tmp/1A1020 /squash/
# ls /squash/
bin  dev  etc  home  lib  linuxrc  mnt  nv  opt  proc  root  run  sbin  sys  tmp  usr  var  www

digging around, there are a number of interesting files:

file	description
/etc/passwd	list of users
/etc/shadow	hashes of users passwords
/etc/init.d/S45Revo	init script for the Revo application
/usr/sbin/telnetd	telnet server binary

20 minutes on a modestly provisioned GCP instance with john yields the passwords:

user	password
default	<redacted*>
revolabs	<redacted*>
root	<redacted*>

• have not reported any issues documented here to Revo Labs, exercise is left to the reader.

looking at the S45Revo file, a potential avenue to uid=0:

14  # restmgr will start telnetd if telnet_enabled uboot env does not exist or is set to 1
15  restmgr &

more to come.

log mining and traffic sniffing

using <dump logs?> functionality, and the high logging levels they provided, was able to determine a number of things:

• it utilizes the pjsua library/client
• it sends a TFTP BOOT request for tftp:///.xml every 30 seconds

next step will be combining the information about the telnet_enabled kernel parameter, and crafting a TFTP configuration that will do just that.