mach_inject causes the injected process to crash after installing Mojave security update 2020-005

[briankendall]

It seemed that after installing Mojave security update 2020-005 mach_inject no longer works. Whichever process gets a payload injected into it will crash. I can reproduce it with mach_inject_example, and it doesn't seem to matter which process I have it inject into.

At this point I'm not sure if any recent updates to macOS 10.15 or one of the Big Sur betas are also affected.

The crash report doesn't seem to be particularly revealing, but it does usually look like this for the crashing thread:

Thread 12 Crashed:
0   ???                           	0x000000010f735fc3 0 + 4554186691
1   libsystem_pthread.dylib       	0x00007fff5b49f2eb _pthread_body + 126
2   libsystem_pthread.dylib       	0x00007fff5b4a2249 _pthread_start + 66
3   libsystem_pthread.dylib       	0x00007fff5b49e40d thread_start + 13

edit: should add this still occurs when SIP is disabled

[saagarjha]

Not seeing any issues on Big Sur, FWIW.

[briankendall]

Doesn't seem to affect Catalina either. Strangely just Mojave 10.14.6 with the latest security update.