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Add support for using the 'dotnet' module in YARA rules #749

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merged 11 commits into from
Apr 23, 2020

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PeterMatula
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run tc tests

@PeterMatula
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run tc tests

// dotnet.user_strings[dotnet.number_of_user_strings - 8] == "{\x001\x001\x001\x001\x001\x00-\x002\x002\x002\x002\x002\x00-\x002\x000\x000\x000\x001\x00-\x000\x000\x000\x000\x001\x00}\x00\x00" and
// dotnet.user_strings[dotnet.number_of_user_strings - 6] == "{\x001\x001\x001\x001\x001\x00-\x002\x002\x002\x002\x002\x00-\x003\x000\x000\x000\x001\x00-\x000\x000\x000\x000\x001\x00}\x00\x00" and
// dotnet.user_strings[dotnet.number_of_user_strings - 4] == "{\x001\x001\x001\x001\x001\x00-\x002\x002\x002\x002\x002\x00-\x004\x000\x000\x000\x001\x00-\x000\x000\x000\x000\x001\x00}\x00\x00" and
// dotnet.user_strings[dotnet.number_of_user_strings - 2] == "{\x001\x001\x001\x001\x001\x00-\x002\x002\x002\x002\x002\x00-\x005\x000\x000\x000\x001\x00-\x000\x000\x000\x000\x001\x00}\x00\x00"
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It seems that there is something wrong with the new YARA rule as the following two tests are failing:

tools.fileinfo.detection.packers.eziriz.EzirizDotnetTest_002 (sample_6.2.0.0_dotnet.exe_ --js[..])  [ FAIL ]  (0.15s)
F
======================================================================
FAIL: test_fileinfo_json_output_is_correctly_parsed (tools.fileinfo.detection.packers.eziriz.EzirizDotnetTest_002)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/tcagent/work/c1867d72f67fc407/retdec-regression-tests/tools/fileinfo/detection/packers/eziriz/test.py", line 38, in test_fileinfo_json_output_is_correctly_parsed
    self.assertEqual(self.fileinfo.output['tools'][0]['name'], 'Eziriz .NET Reactor')
AssertionError: 'Microsoft' != 'Eziriz .NET Reactor'
- Microsoft
+ Eziriz .NET Reactor


----------------------------------------------------------------------
Ran 1 test in 0.002s

FAILED (failures=1)

tools.fileinfo.detection.packers.eziriz.EzirizDotnetTest_002 (sample_6.2.9.2_dotnet.exe_ --js[..])  [ FAIL ]  (0.16s)
F
======================================================================
FAIL: test_fileinfo_json_output_is_correctly_parsed (tools.fileinfo.detection.packers.eziriz.EzirizDotnetTest_002)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/tcagent/work/c1867d72f67fc407/retdec-regression-tests/tools/fileinfo/detection/packers/eziriz/test.py", line 38, in test_fileinfo_json_output_is_correctly_parsed
    self.assertEqual(self.fileinfo.output['tools'][0]['name'], 'Eziriz .NET Reactor')
AssertionError: 'Microsoft' != 'Eziriz .NET Reactor'
- Microsoft
+ Eziriz .NET Reactor


----------------------------------------------------------------------
Ran 1 test in 0.003s

FAILED (failures=1)

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It is worse. I think YARA rule is hitting, but for some reason we filter it out. I run it with vanilla yara and the rule was found.

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@s3rvac, @ladislav-zezula, @metthal
Marek clarified some issues here. This new rule is fundamentally different from other existing rules and cpdetect (and maybe other tools) cannot deal with it. Other rules have strings to match. But this one gets detected, but there are no matches - cpdetect throws it away, This is what would be considered Heuristic rule and until now, we would hardcode it into a C++ source code. I will try to modify the toolchain to deal with it, but I don't know how hard it will be and how many issues I come accross.

@s3rvac s3rvac changed the title Issue 747 yara dotnet module Add support for using the 'dotnet' module in YARA rules Apr 22, 2020
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