Gogs has the ability to import local repositories via Mirror Settings

Description

### Summary The Gogs Mirror Settings functionality provide an alternative way from the well protected New Migration functionality for any authenticated users to import local repositories. This issue stems from a lack of validation of SaveAddress function. ### Details Here is the function implementation of the secure New Migration functionality. <img width="1200" height="755" alt="image" src="https://github.com/user-attachments/assets/a6c2f307-715e-4451-bbc1-7bd934d56f96" /> Here is the function implementation of the Mirror Settings without any validation. <img width="1200" height="477" alt="image" src="https://github.com/user-attachments/assets/a11c41b8-1d08-499c-bce6-ab40844211d7" /> ### PoC The New Migration feature correctly blocked my attempt to import a local repository. <img width="1200" height="1008" alt="image" src="https://github.com/user-attachments/assets/dfc5aa3f-1cc4-427d-b7fe-274363c83c4e" /> But if I create a normal migration with a valid repository. <img width="1200" height="1006" alt="image" src="https://github.com/user-attachments/assets/c96b356e-8ca9-4e79-a69b-ff14593c0cac" /> Then, I could use the Mirror Settings feature under the Repository Settings sync a local repository. <img width="1200" height="476" alt="image" src="https://github.com/user-attachments/assets/9105475c-ae68-4d93-96d5-a3ec356deba7" /> Here is the result after the sync. <img width="1200" height="533" alt="image" src="https://github.com/user-attachments/assets/1df76642-3e55-4493-a422-f7f0619b463d" /> ### Impact Users can import local repositories from the server's filesystem, which allows accessing any repository the git user has access to. There is also a potential issue of blind SSRF.

Affected Packages (1)