We have F-Secure Cloud Protection for Salesforce solution (https://www.f-secure.com/en/web/business_global/cloud-protection-for-salesforce), which can analyze files and URLs uploaded to or downloaded from Salesforce platform. Even if you upload files via Salesforce REST API, F-Secure app will be able scan content and take the action defined in the application settings. Due to the nature and limitations of Salesforce platform, you will not be able to get the scan result before the file is actually uploaded. However, I think you should be able to check the status of the file afterwards--if it is found harmful or malicious, it will be removed.
Hope this helps,
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