An adversary may exfiltrate data in fixed size chunks instead of whole files or limit packet sizes below certain thresholds. This approach may be used to avoid triggering network data transfer threshold alerts.
| ID | Name | Description |
|---|---|---|
| S0622 | AppleSeed |
AppleSeed has divided files if the size is 0x1000000 bytes or more.[1] |
| G0007 | APT28 |
APT28 has split archived exfiltration files into chunks smaller than 1MB.[2] |
| S0030 | Carbanak |
Carbanak exfiltrates data in compressed chunks if a message is larger than 4096 bytes .[3] |
| S0154 | Cobalt Strike |
Cobalt Strike will break large data sets into smaller chunks for exfiltration.[4] |
| S0170 | Helminth |
Helminth splits data into chunks up to 23 bytes and sends the data in DNS queries to its C2 server.[5] |
| S0487 | Kessel |
Kessel can split the data to be exilftrated into chunks that will fit in subdomains of DNS queries.[6] |
| S0699 | Mythic |
Mythic supports custom chunk sizes used to upload/download files.[7] |
| S0644 | ObliqueRAT |
ObliqueRAT can break large files of interest into smaller chunks to prepare them for exfiltration.[8] |
| S0264 | OopsIE |
OopsIE exfiltrates command output and collected files to its C2 server in 1500-byte blocks.[9] |
| S0150 | POSHSPY | |
| S0495 | RDAT |
RDAT can upload a file via HTTP POST response to the C2 split into 102,400-byte portions. RDAT can also download data from the C2 which is split into 81,920-byte portions.[11] |
| G0027 | Threat Group-3390 |
Threat Group-3390 actors have split RAR files for exfiltration into parts.[12] |
| ID | Mitigation | Description |
|---|---|---|
| M1031 | 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. |
| ID | Data Source | Data Component |
|---|---|---|
| DS0029 | Network Traffic | Network Connection Creation |
| Network Traffic Flow |
Analyze network data for uncommon data flows (e.g., a client sending significantly more data than it receives from a server). If a process maintains a long connection during which it consistently sends fixed size data packets or a process opens connections and sends fixed sized data packets at regular intervals, it may be performing an aggregate data transfer. 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. [13]