When I said free software I meant this.
Ccleaner and malware bytes are freemium and freeware. Malware bytes is proprietary software, not sure about ccleaner but probably it is also proprietary.
As for stagefright I dont know but wikipedia search shows this:
The underlying attack vector exploits certain integer overflow vulnerabilities in the Android core component called "Stagefright",[6][7][a] which is a complex software library implemented primarily in C++ as part of the Android Open Source Project (AOSP) and used as a backend engine for playing various multimedia formats such as MP4 files.[5][9]
Search for replicant it is free version of android they found some samsung vulnerability years ago and also there you can find list of what is actually not proprietary in android.
RE: Are open-source projects more or less secure than proprietary ones?