LoFP LoFP / google workspace users typically share drive resources with a shareable link where parameters are edited to indicate when it is viewable or editable by the intended recipient. it is uncommon for a user in an organization to manually copy a drive object from an external drive to their corporate drive. this may happen where users find a useful spreadsheet in a public drive, for example, and replicate it to their drive. it is uncommon for the copied object to execute a container-bound script either unless the user was intentionally aware, suggesting the object uses container-bound scripts to accomplish a legitimate task.

Techniques

Sample rules

Description

Detects when a user copies a Google document, spreadsheet, form, or script from an external Drive into their Workspace Drive and shortly after authorizes a custom Google OAuth application. Adversaries may send spearphishing links with a /copy URI parameter so the victim replicates a malicious object locally. Container-bound Apps Script can then execute on open and prompt the user for OAuth consent, granting the attacker’s application access to Workspace data.

Detection logic

sequence by source.user.email with maxspan=3m
[file where data_stream.dataset == "google_workspace.drive" and event.action == "copy" and

    /* Should only match if the object lives in a Drive that is external to the user's GWS organization */
    google_workspace.drive.owner_is_team_drive == false and google_workspace.drive.copy_type == "external" and

    /* Google Script, Forms, Sheets and Document can have container-bound scripts */
    google_workspace.drive.file.type: ("script", "form", "spreadsheet", "document")]

[any where data_stream.dataset == "google_workspace.token" and event.action == "authorize" and

    /* Ensures application ID references custom app in Google Workspace and not GCP */
    google_workspace.token.client.id : "*apps.googleusercontent.com"]