23 Mar


While doing some research on ILProtector, I loaded my test executable in Olly. To much of my surprise, it refused to run and all I could see in Olly log, was this:

Something smells fishy! wink

I disabled all non-standard plugins, and I was still getting the exception. It was only after I removed the remaining 2 plugins (ScyllaHide and ODBGScript) that my test application launched. Few more restarts and I was sure that ScyllaHide is the one causing the trouble.

OK, I've found a bug in ScyllaHide. But where is it? Which option is causing it? And how can I fix it?

Unfortunately, there is no easy way. Just go through one option after another, until you trigger the bug. 10 minutes and 100 rude words later I was sure that "HeapFlags" is the culprit.

A side note from Captain Obvious

If you're seeing access violation in Olly and want to know where it's happening, make sure you uncheck Ignore Memory access violation in Debugging Options:
olly debugging options
and then run your target:
crash on jit stub
Here we can see that there is a real code at this address - small stub calling mscorwks.dll and that the call comes from ILProtector's protect32.dll.

It immediately gives you plenty of useful information about what's happening. Unfortunately I debugged one instance of Olly from another instance of Olly - got the same results but it took me much longer.


It turns out that .NET Runtime Execution Engine (mscoreei.dll) loves to put executable code on heap:

but ScyllaHide prefers to mark all heaps as non-executable:

and these 2 options kinda conflict with each other. smile

Workaround & fix

This small bug can be used to detect ScyllaHide, as it's enabled by default in all configurations, and tooltip explicitly suggests to leave it as-is:

Very important option, a lot of protectors check for this value.

Here is a suggested patch:

If you don't want to recompile the entire Scylla, here's the binary patch for the official ScyllaHideOlly1.dll from ScyllaHide_v1.3fix_Olly1.rar package:

As a simple workaround, you could uncheck "HeapFlags" in ScyllaHide when debugging .NET applications. However, I would really suggest to fix ScyllaHide instead.

Have fun and keep it safe!

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