Penetration Testing Walkthrough: Bypassing Invitation Code and Accessing the Backend of a Mobile App

The author, presenting himself as a "top architect," describes discovering a mobile application that requires an invitation code for registration and expresses frustration over the lack of open sharing.

Using a virtual machine, the author captures the app's traffic to reveal its real domain, then employs a crawler to locate an undocumented API endpoint (e.g., http://www.xxxxxxx.cn/api/index/tab3?p=1&t=3&v=0&s=0 ) and performs parameter fuzzing to identify missing parameters.

After gathering enough information, the author exploits an SQL injection point to read backend usernames and passwords, successfully logs into the admin panel, and observes that the app has over 10,000 users with a daily increase of 500+.

Within the admin interface, an image upload feature is discovered; the frontend JavaScript validates file types and the backend forcibly renames all uploads to .jpg , making exploitation difficult.

The author contacts the secondary developer (the original author of the modified code), obtains additional credentials, and notes that the software is being sold and used for illicit video distribution.

Despite gaining admin access, the author could not obtain a web shell due to the backend's instability and incomplete exploitation techniques, concluding that the attempt stopped at the admin panel.

Overall, the write‑up provides a practical example of mobile app reconnaissance, API discovery, injection exploitation, and the challenges of bypassing server‑side upload restrictions, serving as a useful case study for information‑security practitioners.