Exfiltration Over Alternative Protocol: Exfiltration Over Symmetric Encrypted Non-C2 Protocol

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).

ID: T1048.001
Sub-technique of:  T1048
Tactic: Exfiltration
Platforms: Linux, Windows, macOS
Data Sources: Malware reverse engineering, Netflow/Enclave netflow, Network protocol analysis, Packet capture, Process use of network
Requires Network:  Yes
Version: 1.0
Created: 15 March 2020
Last Modified: 28 March 2020

Mitigations

Mitigation Description
Filter Network Traffic

Enforce proxies and use dedicated servers for services such as DNS and only allow those systems to communicate over respective ports/protocols, instead of all systems within a network.

Network Intrusion Prevention

Network intrusion detection and prevention systems that use network signatures to identify traffic for specific adversary command and control infrastructure and malware can be used to mitigate activity at the network level.

Network Segmentation

Follow best practices for network firewall configurations to allow only necessary ports and traffic to enter and exit the network.[1]

Detection

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.[2]

Artifacts and evidence of symmetric key exchange may be recoverable by analyzing network traffic or looking for hard-coded values within malware. If recovered, these keys can be used to decrypt network data from command and control channels.

References