This year at S4x15, Digital Bond set out to create an ICS  Capture The Flag, or CTF. Flags were created to simulate real world situations that an attacker would encounter if he targeted an ICS. By the end of the CTF, there were over 30 teams playing. Most of the teams consisted of a single player, however the top scoring teams had multiple team members.

An example of an easy (100 point) and more general forensics flag was to identify the potentially infected machine on the Corporate Zone.  To do this you needed to visit the GigaView TAP Aggregation Switch that Digital Bond had placed within the ICS Village. (A big thanks to Liam Randall at Critical Stack for providing this for our use in the ICS Village.) Once you collected some traffic, you needed to find a host that was trying to perform a DNS lookup of a known malicious site.

Two more flags were related to this infection inside of the Forensics section of the CTF scoreboard. Below is the traffic you would be looking for and once you found this traffic, the host name was the flag


Another flag  that had good feedback from contestants required reading values from a PLC on the network. There were two flags hidden in the Holding Registers of a Modicon PLC. The first one was found in Holding Registers 23 to 33. These values were stored in these registers were decimal representation of ASCII Characters. Depending on the tool you were using this could take some work on converting the numbers found in the registers to ASCII; however, some Modbus Scanners would convert this right out of the box which made it easier for some.


In the same Modicon PLC, there was a flag that consisted of a series of Boolean registers that one needed to convert the binary 1’s and 0’s into ASCII. This flag was rewarded with a higher point value than the other Modbus read flag, as it took more time to concatenate the information back together and convert it to ASCII. Below shows a screenshot of the Holding Registers that were configured with the some of the Boolean values that made up the flag.


A BACnet Flag was hidden inside of an actual BACnet device and could be found on the Internet. There were many different techniques teams used to capture this flag. Some teams downloaded and tried multiple tools, while other teams attempted to modify Digital Bond’s Redpoint script to collect more information to find the Flag. In this case, the Flag was found within the Object Name of an Analog Input inside of the BACnet controller. The Flag is shown below; to find this Flag you would have to read the descriptions of the analog points to know that this Object name was the proper string for the flag.


One Flag (1000 points) proved to be quite difficult, and only one team was able to capture it. This flag was the only 1000 point flag that was found without bending the rules (looking at you team Foobar), and was in the Forensics category. This flag involved using some reverse engineering skills as well as a few hints that were handed out by the judges during the CTF. On the FTP Server in the Corporate zone, there was a Firmware file in a .hex format. In this case, it was a SREC format file. After the team was able to dissemble the file, they were left with assembly code. It was no small task running though the code to find the flag as the flag was hidden inside of an add instruction as shown below. The hex value 0x4841434b then converts to HACK which was the flag.


At the end of the S4x15 CTF, 10 of the 42 Flags were not captured. This is not unusual for a CTF. Out of the remaining flags, some of them were focused around 0-days inside of the ICS based products that were inside of the ICS Village CTF Network. However some of the flags were just overlooked and the judges didn’t give out hints to those flags. Here is the final scoreboard as we shut down the flag submissions:


Over three days the CTF changed leaders a few times with a final result of a team made of Swedes and one Canadian won. Team Foobar won with a final score of 11200 points. The top 10 teams (of which there is single player teams) are as follows:


A big thank you to our sponsors Cisco and mGuard, as well as Checkpoint and Belden for providing hardware for the ICS Village. Without their help, the ICS Village CTF would not have gotten where it did this year. Once again, thanks to all those who played, and we look forward to once again improving the ICS Village next year.