Exfiltration Over Web Service
Where this stands
A Sigma rule exists for this technique in the corpus.
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When a detection for this fires
Collection and exfiltrationData being gathered or moved. This is where a security incident becomes a disclosure obligation.What the technique is
Adversaries may use an existing, legitimate external Web service to exfiltrate data rather than their primary command and control channel. Popular Web services acting as an exfiltration mechanism may give a significant amount of cover due to the likelihood that hosts within a network are already communicating with them prior to compromise. Firewall rules may also already exist to permit traffic to these services. Web service providers also commonly use SSL/TLS encryption, giving adversaries an added level of protection.
Read it on attack.mitre.orgWhat MITRE says you would watch
- AN1511
Processes that normally do not initiate network communications suddenly making outbound HTTPS connections with high outbound-to-inbound data ratios. Defender view: correlation between process creation logs (e.g., Word, Excel, PowerShell) and subsequent anomalous network traffic volumes toward common web services (Dropbox, Google Drive, OneDrive).
- AN1512
Processes (tar, curl, python scripts) accessing large file sets and initiating outbound HTTPS POST requests with payload sizes inconsistent with baseline activity. Defender perspective: detect abnormal sequence of file archival followed by encrypted uploads to external web services.
- AN1513
Office apps or scripts writing files followed by xattr manipulation (to evade quarantine) and subsequent HTTPS uploads. Defender perspective: anomalous file modification + outbound TLS traffic originating from non-networking apps (Word, Excel, Preview).
Technique names and descriptions © MITRE ATT&CK®, CC BY 4.0. Not endorsed by MITRE.