Threat Level: green Handler on Duty: Xavier Mertens

SANS ISC: Malware Victim Selection Through WiFi Identification SANS ISC InfoSec Forums

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Malware Victim Selection Through WiFi Identification

Last week, I found a malware sample that does nothing fancy, it's a data stealer but it has an interesting feature. It's always interesting to have a look at the network flows generated by malware samples. For a while, attackers use GeoIP API services to test if the victim's computer deserves to be infected... or not! By checking the public IP address used by the victim, an attacker might prevent "friends" to be infected (ex: IP addresses from the attacker's country) or if the IP address belongs to a security vendor. On the other side, the attacker might decide to infect the computer because it is located in a specific country or belongs to the targeted organization. There is plenty of free APIs that offer this feature. The ISC API provides also the same kind of details (but only the country)

remnux@remnux:~$ curl -s https://isc.sans.edu/api/ip/195.74.193.12?json | jq '.ip.ascountry'
"BE"

The sample that I found (SHA256:D196E2BBCAF21D3335D72F8E2F2691474BA625E6B01C4DB41A1F91FC41A5EBDF) has a VT score of 41/69[1]. It uses the .Net framework tool regsvcs.exe[2] to execute malicious code extracted by the first stage file. The malware performs the following queries. First, it queries for the victim's public IP address with the help of icanhazip.com:

remnux@remnux:~$ curl -s http://icanhazip.com/
81.246.x.x

The second service used is api.mylnikov.org:

remnux@remnux:~$ curl -s 'https://api.mylnikov.org/geolocation/wifi?v=1.1&bssid=00:0c:29:xx:xx:xx'
{"result":404, "data":{}, "message":6, "desc":"Object was not found", "time":1608552093}

This free service provides geolocation data for WiFi MAC addresses or BSSID. This is also useful to detect the location of the victim. The malware submits the MAC address of the default gateway (in my VM environment) or the BSSID (the MAC address of the wireless access point). In my case, it did not work of course but here is an example of valid BSSID:

remnux@remnux:~$ curl -s 'https://api.mylnikov.org/geolocation/wifi?v=1.1&bssid=00:0C:42:1F:65:E9'
{"result":200, "data":{"lat": 45.22038682066, "range": 141.727, "lon": 16.54741327415, "time": 1608560868}} 

You can see that only latitude and longitude are returned in the JSON data but it's easy to get back the country/city using another public service:

remnux@remnux:~$ curl -s 'https://geocode.xyz/45.22,16.54?geoit=json'| jq '.state'
"BA"

"api.mylnikov.org" seems to be an interesting observable! 

[1] https://www.virustotal.com/gui/file/d196e2bbcaf21d3335d72f8e2f2691474ba625e6b01c4db41a1f91fc41a5ebdf/detection
[2] https://docs.microsoft.com/en-us/dotnet/framework/tools/regsvcs-exe-net-services-installation-tool
[3] https://www.mylnikov.org

Xavier Mertens (@xme)
Senior ISC Handler - Freelance Cyber Security Consultant
PGP Key

I will be teaching next: Reverse-Engineering Malware: Malware Analysis Tools and Techniques - SANS Paris March 2021

Xme

580 Posts
ISC Handler
Dec 22nd 2020

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