Mitsubishi Melsec FX3G-24M Denial Of Service

`OS-S Security Advisory 2015-03  
  
Date: September 29th, 2015  
CVE: CVE-2015-3938  
CVSS: 5 (AV:N/AC:L/Au:N/C:N/I:N/A:P)  
  
Title: Mitsubishi ICS FX3G-24M Permanent Communication Denial of Service  
  
Severity: Critical.   
The TCP/IP communication of the Mitsubishi Melsec FX3G-24 is  
permanently disrupted.   
  
Ease of Exploitation: Trivial  
  
Vulnerability type: Wrong input validation (buffer overflow?)  
  
Products: Mitsubishi Melsec FX3G-24M  
  
Abstract  
The Mitsubishi Melsec FX3G-24M is a highly integrated Industrial Control   
System (ICS). Many functions of the ICS may be controlled via the built-in   
HTTP-Server. By using specially crafted HTTP-messages all Ethernet based   
communication may be permanently disrupted. This permanent denial of Service   
can only be corrected via a cold restart of the ICS.   
Detailed product description  
We confirmed the bug on the following system:  
FX3G-24M   
CPU-Version: 2.10   
FX3U-ENET-ADP Version: 1.20   
Further products or firmware versions have not been tested  
  
Description  
The built-in HTTP application is unable to handle parameters with a length of   
100 bytes or more. This is true for all tested URLs but /fx_devmon.html. Even   
parameters not used by the web applications trigger the DoS bug. This security   
weakness can be exploited using both POST and GET HTTP requests.   
As soon as any parameter with a length of at least 100 characters is   
transmitted all Ethernet/IP/TCP communication is permanently halted. A   
connected HMI looses its connection, the HTTP server is not available any more   
and the System does not respond to ICMP ping requests or ARP requests.  
The ICS has to undergo a cold restart be interrupting the power supply.   
The PLC still continues to execute the internal logic program. Only the   
Ethernet based communication is disrupted.  
  
Proof of Concept  
The following command (all on one line) crafts an GET request and sends it to   
the PLC running on the IP address 192.168.155.80:  
python -c "print 'GET /index.html?'+'A'*100 +' \ HTTP/1.1\r\n\r\n'" | nc   
192.168.155.80 80  
  
As soon as the command returns the communication is disrupted.  
  
Severity and Ease of Exploitation  
The security weakness can be easily exploited. No special tools are necessary.   
The Exploit neither requires physical access to the ICS nor does it require   
direct access to the ICS network. The exploit can be executed across routers   
and if the ICS is connected to the internet across the Internet. The HTTP-  
request is a normal and valid request and will not be detected or prevented by   
Firewalls or Intrusion Prevention Systems.  
The disruption of the Ethernet based communication will cause a permanent loss   
of view on any connected HMIs and will prevent the communication of the ICS   
with other ICS systems via Ethernet.  
  
Vendor Communication  
We unsuccessfully tried to contact the vendor for several month. We could not   
find a security contact responsible for these products. On December 4th 2014   
we contacted the ICS-CERT. The ICS-CERT contacted Mitsubishi. Mitsubishi   
released a new firmware in April 2015. The new firmware will only be available   
in all controllers shipped starting April 2015. Older controllers will not   
receive the firmware update.   
  
Formatted PDF:   
--   
OpenSource Security Ralf Spenneberg http://www.os-s.de  
Am Bahnhof 3-5 48565 Steinfurt Germany  
Fon: +49(0)2552 638 755 Fax: +49(0)2552 638 757  
`