Exfiltration Over Symmetric Encrypted Non-C2 Protocol
Where this stands
One published detection covers this technique. Every one is unverified — no rule on Siemphony has been executed against real telemetry.
What the technique is
Adversaries may steal data by exfiltrating it over a symmetrically encrypted network protocol other than that of the existing command and control channel. The data may also be sent to an alternate network location from the main command and control server. Symmetric encryption algorithms are those that use shared or the same keys/secrets on each end of the channel. This requires an exchange or pre-arranged agreement/possession of the value used to encrypt and decrypt data. Network protocols that use asymmetric encryption often utilize symmetric encryption once keys are exchanged, but adversaries may opt to manually share keys and implement symmetric cryptographic algorithms (ex: RC4, AES) vice using mechanisms that are baked into a protocol. This may result in multiple layers of encryption (in protocols that are natively encrypted such as HTTPS) or encryption in protocols that not typically encrypted (such as HTTP or FTP).
Read it on attack.mitre.orgWhat MITRE says you would watch
- AN1389
Detects the execution of non-browser processes establishing outbound encrypted network connections using uncommon symmetric encryption protocols (e.g., AES via PowerShell or custom scripts) to alternate external destinations.
- AN1390
Detects command-line utilities or scripts using encryption libraries or symmetric algorithms (e.g., OpenSSL AES, GPG, Python + PyCrypto) in conjunction with outbound file transfers or traffic to external destinations.
- AN1391
Detects symmetric key-based encryption operations (e.g., AES via Python, AppleScript, or OpenSSL) followed by unusual outbound connections from non-browser applications or scripted tools.
Technique names and descriptions © MITRE ATT&CK®, CC BY 4.0. Not endorsed by MITRE.