Spearphishing with a link is a specific variant of spearphishing. It is different from other forms of spearphishing in that it employs the use of links to download malware contained in email, instead of attaching malicious files to the email itself, to avoid defenses that may inspect email attachments.
All forms of spearphishing are electronically delivered social engineering targeted at a specific individual, company, or industry. In this case, the malicious emails contain links. Generally, the links will be accompanied by social engineering text and require the user to actively click or copy and paste a URL into a browser, leveraging User Execution. The visited website may compromise the web browser using an exploit, or the user will be prompted to download applications, documents, zip files, or even executables depending on the pretext for the email in the first place. Adversaries may also include links that are intended to interact directly with an email reader, including embedded images intended to exploit the end system directly or verify the receipt of an email (i.e. web bugs/web beacons).
Patchwork has used spearphishing with links to deliver files with exploits to initial victims. The group has used embedded image tags (known as web bugs) with unique, per-recipient tracking links in their emails for the purpose of identifying which recipients opened messages.
Because this technique involves user interaction on the endpoint, it's difficult to fully mitigate. However, there are potential mitigations. Users can be trained to identify social engineering techniques and spearphishing emails with malicious links. Other mitigations can take place as User Execution occurs.
URL inspection within email (including expanding shortened links) can help detect links leading to known malicious sites. Detonation chambers can be used to detect these links and either automatically go to these sites to determine if they're potentially malicious, or wait and capture the content if a user visits the link.
Because this technique usually involves user interaction on the endpoint, many of the possible detections for Spearphishing Link take place once User Execution occurs.
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