How can I access the members-only video comment? | YouTube ($5,000)

Steps to reproduce:

1. Go to the victim video. (members-only video)

Response:

"Join this channel from your computer or Android app to get access to members-only content like this video."

You must join to access the video and video comment.

2. Upload video.
3. Open the video: https://m.youtube.com/watch?v=your_video_id
4. Click "Comments".

Request:

[GET] https://m.youtube.com/watch_comment?action_get_comments=1&ctoken=...&pbj=1

---

URL decode:

URL decode:

Base64 decode:

Change to victim_video_id.

Base64 encode:

URL encode:

URL encode:

---

Response:

---

---

Attacker can access the members-only video comment.

PoC video: https://youtu.be/6wVKbCkSe3E


Timeline:

mm/dd/yyyy

05/15/2021 - Bug Found
05/15/2021 - Submit Report
05/17/2021 - Triaged
    Priority: P4 - P2
    Status: New - Assigned
05/21/2021 - 🎉 Nice catch!
    Type: Customer Issue - Bug
    Severity: S4 - S2
    Status: Assigned - Accepted
05/28/2021 - Bounty awarded by Google VRP. ($5,000)
02/07/2022 - Fixed

LinkedIn: Alessandro Rumampuk
YouTube: R,ando
Facebook: Ando
Twitter: R ando