One-Way Communication
Where this stands
A reviewer read the telemetry and concluded there is nothing here to detect that a sibling technique does not already cover.
All three analytics define the observable as an absence, which lib/sigma cannot express: AN1599 is 'outbound connections to web services without corresponding response or return traffic', AN1600 is 'with no observed response parsing logic', AN1601 is 'without any response handling'. Proving one-wayness needs a second event that never arrives, plus a TimeWindow — no aggregation, no timeframe, no cross-event join is available per hard rule 4. What is left after dropping the absence is already published twice in this corpus on the identical logsource and fields. […]
What the technique is
Adversaries may use an existing, legitimate external Web service as a means for sending commands to a compromised system without receiving return output over the Web service channel. Compromised systems may leverage popular websites and social media to host command and control (C2) instructions. Those infected systems may opt to send the output from those commands back over a different C2 channel, including to another distinct Web service. Alternatively, compromised systems may return no output at all in cases where adversaries want to send instructions to systems and do not want a response. Popular websites and social media acting as a mechanism for C2 may give a significant amount of cover due to the likelihood that hosts within a network are already communicating with them prior to a compromise. Using common services, such as those offered by Google or Twitter, makes it easier for adversaries to hide in expected noise. Web service providers commonly use SSL/TLS encryption, giving adversaries an added level of protection.
Read it on attack.mitre.orgWhat MITRE says you would watch
- AN1599
Suspicious process initiating outbound connections to web services without corresponding response or return traffic, indicative of one-way command channels.
- AN1600
Curl, wget, or custom HTTP clients initiated by uncommon user accounts or cron jobs to popular web services, with no observed response parsing logic.
- AN1601
Process using URLSession or similar API to fetch from web services without any response handling, indicative of one-way C2 channels.
Technique names and descriptions © MITRE ATT&CK®, CC BY 4.0. Not endorsed by MITRE.