PsiTransfer: File integrity violation

Summary

The absence of restrictions on the endpoint, which is designed for uploading files, allows an attacker who received the id of a file distribution to change the files that are in this distribution.

Details

Vulnerable endpoint: PATCH /files/{{id}}

PoC

1. Create a file distribution.

2. Go to the link address for downloading files and download the file (in this case, the attacker receives the file id from the download request).

3. Send a PATCH /files/{{id}} request with arbitrary content in the request body.

Thus, the file with the specified id will be changed. What the attacker specifies in the body of the request will be added to the end of the original content. In the future, users will download the modified file.

Impact

The vulnerability allows an attacker to influence those users who come to the file distribution after him and slip the victim files with a malicious or phishing signature.