D-Link DSR-250N Denial Of Service

`Advisory: Denial of Service in D-Link DSR-250N  
  
RedTeam Pentesting discovered a Denial-of-Service vulnerability in the  
D-Link DSR-250N device which allows unauthenticated attackers in the  
same local network to execute a CGI script which reboots the device.  
  
  
Details  
=======  
  
Product: D-Link DSR-250N  
Affected Versions: 3.12 and potentially later  
Fixed Versions: 3.17B  
Vulnerability Type: DoS  
Security Risk: low  
Vendor URL: https://www.dlink.com/en/products/dsr-250n-wireless-n-unified-service-router  
Vendor Status: notified  
Advisory URL: https://www.redteam-pentesting.de/advisories/rt-sa-2020-002  
Advisory Status: published  
CVE: CVE-2020-26567  
CVE URL: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-26567  
  
  
Introduction  
============  
  
"The D-Link Wireless N Unified Service Router (DSR-250N) provides  
enhanced security, functionality and performance over a traditional VPN  
router without the complexity of a full firewall solution. The D-Link  
Wireless N Unified Service Router is a cost-effective, high performance  
solution for securing a small business network."  
  
(from the vendor's homepage)  
  
  
More Details  
============  
  
During a penetration test, the firmware for the D-Link DSR-250N router  
was downloaded from D-Links official website[1] and extracted for  
further analysis. It was then confirmed that CGI scripts exist on the  
router that can be directly accessed with a web browser, without any  
authentication. In particular, the script "upgradeStatusReboot.cgi"  
executes the command to reboot the device. Its contents are:  
  
------------------------------------------------------------------------  
#!/bin/sh  
echo Content-type: text/plain  
echo ""  
stat=`/sbin/reboot -d 8 &`  
echo $stat  
------------------------------------------------------------------------  
  
Executing this script renders the device unusable for the time of the  
reboot. In tests, it turned out that the device needs roughly four  
minutes to complete a reboot. As a consequence, any network using the  
device as a switch or router is not accessible during that time, too.  
  
In the penetration test, the router's web interface was available  
directly over the Internet. According to the vendor, the web interface  
is by default disabled for the WAN interface.  
  
  
Proof of Concept  
================  
  
An HTTP GET request to the CGI script "upgradeStatusReboot.cgi" will  
reboot the device:  
  
------------------------------------------------------------------------  
$ curl -k -s https://IP-ADDRESS/scgi-bin/upgradeStatusReboot.cgi  
------------------------------------------------------------------------  
  
  
Workaround  
==========  
  
Access to the D-Link DSR-250N's web interface should only be enabled for  
administrators, for example by only allowing access from specific IP  
addresses in the firewall. Access over the WAN interface should also be  
disabled if it was enabled manually.  
  
  
Fix  
===  
  
A preview firmware version named 3.17B which should correct the issue  
was received at the end of September from the vendor. RedTeam Pentesting  
was not able to verify the fix due to lack of access to a test device.  
However, the formerly accessible CGI script is no longer part of the  
firmware.  
  
  
Security Risk  
=============  
  
No authentication is needed to excute the CGI script and thereby reboot  
the device. Attackers might abuse this behaviour for targeted  
denial-of-service-attacks against D-Link customers, since rebooting the  
device interrupts access to networks relying on this device for routing  
or switching purposes. However, the attack is only possible if the  
attacker resides on the same network, and no further information can be  
gathered or control over the devices be obtained. Therefore, the  
vulnerability is rated as a low risk.  
  
  
Timeline  
========  
  
2020-06-29 Vulnerability identified  
2020-07-03 Customer approved disclosure to vendor  
2020-07-03 Requested security contact from vendor via web formular  
2020-07-03 Vendor replied with contact information  
2020-07-07 Advisory provided to vendor  
2020-09-28 Vendor provided fixed version to RedTeam Pentesting  
2020-10-05 CVE ID requested  
2020-10-06 CVE ID assigned  
2020-10-08 Advisory released  
  
  
References  
==========  
  
[1] https://support.dlink.com/ProductInfo.aspx?m=DSR-250N  
  
  
RedTeam Pentesting GmbH  
=======================  
  
RedTeam Pentesting offers individual penetration tests performed by a  
team of specialised IT-security experts. Hereby, security weaknesses in  
company networks or products are uncovered and can be fixed immediately.  
  
As there are only few experts in this field, RedTeam Pentesting wants to  
share its knowledge and enhance the public knowledge with research in  
security-related areas. The results are made available as public  
security advisories.  
  
More information about RedTeam Pentesting can be found at:  
https://www.redteam-pentesting.de/  
  
  
Working at RedTeam Pentesting  
=============================  
  
RedTeam Pentesting is looking for penetration testers to join our team  
in Aachen, Germany. If you are interested please visit:  
https://www.redteam-pentesting.de/jobs/  
  
--   
RedTeam Pentesting GmbH Tel.: +49 241 510081-0  
Dennewartstr. 25-27 Fax : +49 241 510081-99  
52068 Aachen https://www.redteam-pentesting.de  
Germany Registergericht: Aachen HRB 14004  
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`