ParanoidAndroid So it is already reported (https://gitlab.com/fdroid/fdroidserver/-/merge_requests/1466#note_2281771672) that this issue would not significantly impact apps in the f-droid.org repo.
Thank you for this link. It answers the question I had, what the implications for this certificate pinning vulnerability is.
Actually, according to F-Droid developers looking into this security vulnerability, it does not affect the default F-Droid repository at all, as the vulnerable functionality isn't even being used. All APKs have also been scanned, as an extra precaution, no signs of any tampering. Some third-party repositories might be using the vulnerable functionality, so they are working on a fix with high priority.
It is still not clear to me where it is they are using certificate pinning or why, but that question is not so important to answer anymore, as they are doing it in some very specific optional and disabled by default configuration only, according to F-Droid developers.
ParanoidAndroid I always been thinking about the situation like this:
PlayStore: relatively high security but not always safe to install (there was malware in the past)
F-Droid: relatively low risk of installing malware if build by F-Droid and you need to trust the dev if the build is reproducible - risk of signature pinning but this would not affect already installed apps right?
directly from Source: You need to trust the developer and the Source that the uploaded binary is safe
Is my picture of this situation correct? Am I missing out significant points? If I am correct, would it be that dumb to keep using F-Droid for updates?
I would say you have about the same protection from generic malware in both Google Play and F-Droid. The important thing is that they would both remove an app from their repository the moment someone reports there is malicious code in the app or its source code. And they will both make sure they have the genuine version of a certain branded app, and remove any non-genuine versions as soon as it would be reported to them. This is the big level of protection you get, root of trust. You don't get that if getting the app directly from the developer, on github or similar (unless the app happens to be in AppVerifier, in which case you can verify it anyway).
Personally I would never trust Google Play Services or any Google integrations in my threat model, since Google is one of the parties that has acted hostile towards my minority. The risk they would inject code to spy on us is maybe not that big, but the risk F-Droid or anyone in the open source community would is way way smaller. I looked into getting Google Play Services free versions of my privacy sensitive F-Droid apps directly from the developers, but they say no, use F-Droid. They only publish the Google Play version of their apps on github.