T1566.003: Spearphishing via Service

Adversaries may send spearphishing messages via third-party services in an attempt to gain access to victim systems. Spearphishing via service is a specific variant of spearphishing. It is different from other forms of spearphishing in that it employs the use of third party services rather than directly via enterprise email channels.

All forms of spearphishing are electronically delivered social engineering targeted at a specific individual, company, or industry. In this scenario, adversaries send messages through various social media services, personal webmail, and other non-enterprise controlled services. These services are more likely to have a less-strict security policy than an enterprise. As with most kinds of spearphishing, the goal is to generate rapport with the target or get the target's interest in some way. Adversaries will create fake social media accounts and message employees for potential job opportunities. Doing so allows a plausible reason for asking about services, policies, and software that's running in an environment. The adversary can then send malicious links or attachments through these services.

A common example is to build rapport with a target via social media, then send content to a personal webmail service that the target uses on their work computer. This allows an adversary to bypass some email restrictions on the work account, and the target is more likely to open the file since it's something they were expecting. If the payload doesn't work as expected, the adversary can continue normal communications and troubleshoot with the target on how to get it working.

Positive Technologies products that cover the technique

MaxPatrol SIEM knowledge base

remote_work: PT-CR-2552: Possible_Mail_Spoofing_Attack: Fake email in which the name in the SMTP envelope does not match the name in the email header. This may indicate email spoofing.

Detection

IDDS0029Data source and componentNetwork Traffic: Network Traffic FlowDescription

Monitor network data for uncommon data flows. Processes utilizing the network that do not normally have network communication or have never been seen before are suspicious.

IDDS0029Data source and componentNetwork Traffic: Network Traffic ContentDescription

Monitor and analyze traffic patterns and packet inspection associated to protocol(s) that do not follow the expected protocol standards and traffic flows (e.g extraneous packets that do not belong to established flows, gratuitous or anomalous traffic patterns, anomalous syntax, or structure). Consider correlation with process monitoring and command line to detect anomalous processes execution and command line arguments associated to traffic patterns (e.g. monitor anomalies in use of files that do not normally initiate connections for respective protocol(s)).

IDDS0015Data source and componentApplication Log: Application Log ContentDescription

Monitor for third-party application logging, messaging, and/or other artifacts that may send spearphishing messages via third-party services in an attempt to gain access to victim systems.

Mitigation

IDM1017NameUser TrainingDescription

Users can be trained to identify social engineering techniques and spearphishing messages with malicious links.

IDM1021NameRestrict Web-Based ContentDescription

Determine if certain social media sites, personal webmail services, or other service that can be used for spearphishing is necessary for business operations and consider blocking access if activity cannot be monitored well or if it poses a significant risk.

IDM1049NameAntivirus/AntimalwareDescription

Anti-virus can also automatically quarantine suspicious files.