HackerOne: Blind XSS in app.pullrequest.com/████████ via /reviews/ratings/{uuid}

Summary:
Hi,

While researching PullRequest yesterday, I saw some “review” endpoints in web archive of “app.pullrequest.com”. (http://web.archive.org/cdx/search/cdx?url=app.pullrequest.com/*&output=text&fl=original&collapse=urlkey)

One of them was https://app.pullrequest.com/reviews/ratings/6eaa6b75-b958-4530-ba46-0d00cbe74e0b/false , I went to that endpoint and filled the all fields with my blind XSS payload.
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This payload sends an alert to my blind XSS application in ██████

Today (May 3, 2022, 6:09 pm UTC+3), I got a lot of alerts from https://app.pullrequest.com/███. I checked the report and I see it came from an PullRequest admin who checks reviews.

Here is a screenshot from the report :

███████

I checked the HTML source code and I see my payload reflected to Disliked_reviewers, Liked_reviewers and Reasons fields without any encoding.

You can also check the source code : █████████

Impact

Blind XSS in PullRequest admin portal

Regards,
Bugra