Spearphishing via Service

What the technique is

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. […]

What MITRE says you would watch

• AN0320

  Inbound spearphishing attempts delivered via third-party services (e.g., Gmail, LinkedIn messages) leading to malicious file downloads or browser-initiated script execution. Defender view includes correlation of external service logins, unexpected file write operations, and suspicious descendant processes spawned from productivity or browser applications.

• AN0321

  Use of non-enterprise email or messaging services in Thunderbird, Evolution, or browsers leading to suspicious file downloads and subsequent execution. Defender view includes browser-initiated downloads of unexpected content and shell or interpreter processes launched post-download.

• AN0322

  Phishing attempts via iCloud Mail, Gmail, or social media apps accessed on macOS systems. Defender view includes Mail.app or Safari downloads of files followed by osascript, Terminal, or abnormal child process execution.