Unusual Activity with Double Base64 Encoding

Published: 2019-10-27
Last Updated: 2019-10-27 12:59:10 UTC
by Guy Bruneau (Version: 1)
2 comment(s)

This week I found this traffic in my honeypot, my first impression, it didn't look that unusual since Base64 encoding is used quite a bit to encode traffic to a web server. Using CyberChef, I decoded the Base64 portion to see what it was all about only to find out it was further encoded in Base64. Decoding the second Base64 revealed two IP address in it.

However, the interesting part after decoding it was the IPs were already in the traffic payload. The first IP was the source of the traffic (

TmpBdU1Ua3hMalV5TGpJMU5Dd3hNVEl1TVRjdU1USTFMakU0TUE9PQ== → NjAuMTkxLjUyLjI1NCwxMTIuMTcuMTI1LjE4MA== →, → ISC reports shows scanning for 1723 and 3128 → No ISC reports → No ISC reports. Hangzhou Alibaba Advertising Co.,Ltd., CN

Another search of my logs revealed this kind of activity had been happening for quite a while and it is always the exact same query down to the IPs and ports. I have logs for this activity since February this year on port 80 and 8088. and the same high port (63435) used in all the traffic. A search in for BS_REAL_IP shows other honeypots[2].

Here is a copy of the raw log:

tcp-honeypot-20191019-075047.log:20191025-222956: data 'HEAD HTTP/1.1\r\nAccept-Encoding: gzip\r\nUser-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/53.0.2785.143 Safari/537.36\r\nBS_REAL_IP: TmpBdU1Ua3hMalV5TGpJMU5Dd3hNVEl1TVRjdU1USTFMakU0TUE9PQ==\r\nHost:\r\nAccept: text/html, image/gif, image/jpeg, *; q=.2, */*; q=.2\r\nProxy-Connection: keep-alive\r\n\r\n'

Generic Code beautify by CyberChef:

Accept-Encoding: gzip
User-Agent: Mozilla/5.0 (Macintosh
 Intel Mac OS X 10_11_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/53.0.2785.143 Safari/537.36
Accept: text/html, image/gif, image/jpeg,
Proxy-Connection: keep-alive

[1] https://isc.sans.edu/ipdetails.html?ip=
[2] https://www.abuseipdb.com/check/

Guy Bruneau IPSS Inc.
My Handler Page
Twitter: GuyBruneau
gbruneau at isc dot sans dot edu

2 comment(s)


very interesting
That is... different.
An attempt to further obfuscate information about the C2 environment(s) maybe?

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