Data Transfer Size Limits

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: T1030
Sub-techniques:  No sub-techniques
Tactic: Exfiltration
Platforms: Linux, Windows, macOS
Data Sources: Network Traffic: Network Connection Creation, Network Traffic: Network Traffic Flow
Requires Network:  Yes
Version: 1.0
Created: 31 May 2017
Last Modified: 14 July 2020

Procedure Examples

ID Name Description
S0030 Carbanak

Carbanak exfiltrates data in compressed chunks if a message is larger than 4096 bytes .[1]

S0170 Helminth

Helminth splits data into chunks up to 23 bytes and sends the data in DNS queries to its C2 server.[2]

S0487 Kessel

Kessel can split the data to be exilftrated into chunks that will fit in subdomains of DNS queries.[3]

S0264 OopsIE

OopsIE exfiltrates command output and collected files to its C2 server in 1500-byte blocks.[4]

S0150 POSHSPY

POSHSPY uploads data in 2048-byte chunks.[5]

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.[6]

G0027 Threat Group-3390

Threat Group-3390 actors have split RAR files for exfiltration into parts.[7]

Mitigations

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.

Detection

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. [8]

References