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--- script:x509_ext_c2 [2018/02/08 23:51] – [Analysing the sample PCAP in Trisul] veera
+++ script:x509_ext_c2 [2018/02/08 23:53] – [Detecting covert channels in X.509 Digital Certificates using the Trisul LUA API] veera
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 I saw a couple of blogs about a new way to create a C2 (Command and Control) channel using X.509 Certificates. This technique is described in //Abusing X.509 Certificates for Covert Data Exchange// ((Dark Reading https://www.darkreading.com/attacks-breaches/abusing-x509-digital-certificates-for-covert-data-exchange/d/d-id/1330984?_mc=sm_dr&hootPostID=a10970e131beaf9b5a7ac86b0564b114))  and the original link on the //Fidelis Blog Whats missing is in front of us// ((Fidelis Security Blog https://www.fidelissecurity.com/threatgeek/2018/02/exposing-x509-vulnerabilities)) and also on the //Network Miner blog Examining a X.509 Covert Channel// (( Network Miner blog post https://www.fidelissecurity.com/threatgeek/2018/02/exposing-x509-vulnerabilities )) I'd also like to mention the author [[https://twitter.com/sysopfb|Jason Reaves]]
-In this technique the covert channel is built by stuffing chunks of data into  X.509 Certificate Extensions, in this case the "Subject Key Identifier" aka SKI extension. This is usually a hash of 20 bytes.  However this is not used in certificate validation and it appears from the researchers that the network defenses are not checking if this contains a valid value.  The C2 POC uses a large number of certificates with SKI values of 10,000 bytes !
+In this technique the covert channel is built by stuffing chunks of data into  X.509 Certificate Extensions, in this case the "Subject Key Identifier" aka SKI extension. This is usually a hash of 20 bytes.  However this is not used in certificate validation and it appears current commercial network defenses are not checking if this contains a valid value.  The C2 POC uses a large number of certificates with SKI values of 10,000 bytes !
 Detecting this is quite easy with Trisul as well as Bro IDS. This post highlights the different approaches taken.