Niantic Labs' cat-and-mouse game with Pokémon Go cheaters has led to many instances of innocent players being locked out of the game. Only a few months ago, owners of some Xiaomi devices had their accounts suspended for no fault of their own, and now Niantic is seemingly cracking down on players with custom recoveries installed.

Custom recovery partitions allow you to flash custom ROMs, install root, make full device backups, and perform other functions. While they could theoretically be used for cheating, Pokémon Go is now blocking players if custom recoveries are detected at all, according to a few reports on Reddit and Twitter.

Source: Kieron Quinn (Twitter)

The check seems to have been added in the recent v0.167.0 update, and involves searching the internal storage of your phone for directories named 'TWRP' (corresponding to the TeamWin Recovery Project recovery) or 'Fox' (the folder for OrangeFox recovery). I wasn't able to duplicate this myself on a OnePlus 7 Pro by creating those folders manually, but the block could be part of a server-side component that hasn't widely rolled out.

Interestingly, Pokémon Go doesn't even ask for the external storage permission to check for the TWRP folder. Kieron Quinn pointed out on Twitter that the game is likely using a bug in Android that allows apps to check if directories are present without being granted storage permission.

Would Scoped Storage actually prevent this? PoGo does this without READ_EXTERNAL_STORAGE by abusing a bug in ls, so it's not even using the current permissions correctly.

I think the bug got patched anyway didn't it? — Kieron Quinn (@Quinny898) February 17, 2020

It has not been patched, at least on Oxygen OS Android 10 (storage permission denied) Will have to run some tests to see if it still works on an app with Scoped Storage. pic.twitter.com/njDgIOaI0I — Kieron Quinn (@Quinny898) February 18, 2020

For the record, Scoped Storage would prevent bugs like this from working at all, since apps would no longer have access to your phone's root directory. There are still only a few reports of players being blocked in this manner, but even one ban for simply having a custom recovery installed is too many.