Standard Cryptographic Protocol
|Standard Cryptographic Protocol|
|Tactic||Command and Control|
|Platform||Linux, macOS, Windows|
|Data Sources||Packet capture, Netflow/Enclave netflow, Malware reverse engineering, Process use of network, Process monitoring, SSL/TLS inspection|
Adversaries use command and control over an encrypted channel using a known encryption protocol like HTTPS or SSL/TLS. The use of strong encryption makes it difficult for defenders to detect signatures within adversary command and control traffic.
Some adversaries may use other encryption protocols and algorithms with symmetric keys, such as RC4, that rely on encryption keys encoded into malware configuration files and not public key cryptography. Such keys may be obtained through malware reverse engineering.
- APT34 used the Plink utility and other tools to create tunnels to C2 servers.1
- BRONZE BUTLER has used RC4 encryption (for Datper malware) and AES (for xxmm malware) to obfuscate HTTP traffic.2
- FIN6 used the Plink command-line utility to create SSH tunnels to C2 servers.3
- FIN8 has used the Plink utility to tunnel RDP back to C2 infrastructure.4
- Lazarus Group malware uses Caracachs encryption to encrypt C2 payloads.5
- Stealth Falcon malware encrypts C2 traffic using RC4 with a hard-coded key.6
- Taidoor uses RC4 to encrypt the message body of HTTP content.7
- 3PARA RAT command and control commands are encrypted within the HTTP C2 channel using the DES algorithm in CBC mode with a key derived from the MD5 hash of the string HYF54&%9&jkMCXuiS.8
- A variant of ADVSTORESHELL encrypts some C2 with 3DES and RSA.9
- CHOPSTICK encrypts C2 communications with RC4 as well as TLS.10
- CallMe uses AES to encrypt C2 traffic.11
- Carbanak encrypts the message body of HTTP traffic with RC2 and Base64 encoding.12
- ChChes can encrypt C2 traffic with AES.1314
- Chaos provides a reverse shell connection on 8338/TCP, encrypted via AES.15
- Daserf uses RC4 encryption to obfuscate HTTP traffic.2
- Dipsind encrypts C2 data with AES256 in ECB mode.16
- Downdelph uses RC4 to encrypt C2 responses.17
- The Duqu command and control protocol's data stream can be encrypted with AES-CBC.18
- Elise encrypts exfiltrated data with RC4.19
- Some variants of FakeM use RC4 to encrypt C2 traffic.11
- Some Felismus samples use AES to encrypt C2 traffic.20
- H1N1 encrypts C2 traffic using an RC4 key.21
- Helminth encrypts data sent to its C2 server over HTTP with RC4.22
- MobileOrder uses AES to encrypt C2 communications.11
- MoonWind encrypts C2 traffic using RC4 with a static key.23
- NETEAGLE will decrypt resources it downloads with HTTP requests by using RC4 with the key "ScoutEagle."24
- Nidiran uses RC4 to encrypt C2 traffic.25
- POSHSPY encrypts C2 traffic with AES and RSA.26
- POWERSTATS has encrypted C2 traffic with RSA.27
- PoisonIvy uses the Camellia cipher to encrypt communications.28
- Prikormka encrypts some C2 traffic with the Blowfish cipher.29
- Pupy's default encryption for its C2 communication channel is SSL, but it also has transport options for RSA and AES.30
- APT12 has used the RIPTIDE RAT, which communicates over HTTP with a payload encrypted with RC4.31
- RedLeaves encrypts C2 traffic with RC4 using a secret key of 88888888.32
- Remsec's network loader encrypts C2 traffic with RSA and RC6.33
- SNUGRIDE encrypts C2 traffic using AES with a static key.34
- SeaDuke C2 traffic has been encrypted with RC4 and AES.3536
- Some Volgmer use SSL to encrypt C2 communications.37
- XTunnel uses SSL/TLS and RC4 to encrypt traffic.3810
- ZeroT has used RC4 to encrypt C2 traffic.3940
- adbupd contains a copy of the OpenSSL library to encrypt C2 traffic.16
Network intrusion detection and prevention systems that use network signatures to identify traffic for specific adversary malware can be used to mitigate activity at the network level. Use of encryption protocols may make typical network-based C2 detection more difficult due to a reduced ability to signature the traffic. Prior knowledge of adversary C2 infrastructure may be useful for domain and IP address blocking, but will likely not be an effective long-term solution because adversaries can change infrastructure often.41
SSL/TLS inspection is one way of detecting command and control traffic within some encrypted communication channels.42 SSL/TLS inspection does come with certain risks that should be considered before implementing to avoid potential security issues such as incomplete certificate validation.43
If malware uses encryption with symmetric keys, it may be possible to obtain the algorithm and key from samples and use them to decode network traffic to detect malware communications signatures.44
In general, analyze network data for uncommon data flows (e.g., a client sending significantly more data than it receives from a server). Processes utilizing the network that do not normally have network communication or have never been seen before are suspicious. Analyze packet contents to detect communications that do not follow the expected protocol behavior for the port that is being used.41
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