Elastic Defend high stable eql
AMSI Bypass from Suspicious Module
Identifies attempts to modify the permissions or write to Microsoft Anti Malware Scan Interface DLL from unsigned module.
Detection Logic
api where process.Ext.api.metadata.target_address_name like "amsi.dll*" and
((process.Ext.api.name in ("VirtualProtect", "VirtualProtectEx") and process.Ext.api.parameters.protection like "?W*") or
process.Ext.api.name == "WriteProcessMemory") and
not process.thread.Ext.call_stack_final_user_module.protection_provenance like "Kernel*" and
not process.thread.Ext.call_stack_final_user_module.name in ("Kernel", "Unknown", "Undetermined") and
not process.thread.Ext.call_stack_final_user_module.hash.sha256 in
("2ef4add3ecdc20e1234b0c3fa034cf110f5dfc01355f81ed773f797fcdc6a375",
"c2710daef53ff962522ec1e7e05cdc7147db3371dfbc71cb1cf7afe6382451e5",
"15dd664aee6bfd3cbe0a967d160f4f4b37fe3e8aef88dfb4547e77292226c0c4",
"a121de30d1b8cdf66d886f8cd02b4a35d477f2638d616673da76716a9466cae7",
"ce0644768cd505a8975d897a560186011fbcd2cbd6b309eb0688fc4d816a3451",
"23217cdb3ff108ee4e099f61afa6e33f65675ae0c25d7cc0a30554deca1b33dc",
"d0c7983d45bbbe52e10aa461226cef4049d30778a5d03c9663251edbcea5bd6e",
"b6f6b9f49c60a2230cbf1a3449c85434b70a3b46cc3727da3ef265ba46ac4967",
"902080ae0b0348dca5d526b8cefee280fec0e4eb7299af211ad522e6644032f4",
"5eea4cecd56c5c12f748a2c06729448419ca4deec2410314b6e9d184ecf64bad",
"384c31b964bac7f60c637ed032d735537adebf3611f78637887d042330655f24",
"4776e752dab37e0540f4f3b66a6686e549a9eba42ddfe2f22ee8bcd8e11d215e",
"3505e9318d1ca3472c7708ebaa1753b5cc0eda43c6f5210807a9e7ca8673a227",
"1ee57272a271e82eee1aebaab306c403b30a2e9df94ede777f17fe84670e5033") and
(
_arraysearch(process.thread.Ext.call_stack_final_user_module.code_signature, $entry, $entry.trusted == false or $entry.exists == false) or
_arraysearch(process.thread.Ext.call_stack_final_user_module.code_signature, $entry, $entry.subject_name in ("Microsoft Corporation", "Microsoft Windows", ".NET", "Python Software Foundation"))
) and
not _arraysearch(process.thread.Ext.call_stack_final_user_module.code_signature, $entry, $entry.trusted == true and
$entry.subject_name in ("Microsoft Windows Hardware Compatibility Publisher",
"Microsoft Windows Software Compatibility Publisher",
"MUSARUBRA US LLC")) and
not process.thread.Ext.call_stack_final_user_module.path like
("c:\\windows\\system32\\apphelp.dll",
"c:\\windows\\system32\\lsasrv.dll",
"c:\\windows\\system32\\combase.dll",
"c:\\windows\\system32\\ieadvpack.dll",
"c:\\windows\\syswow64\\*.dll",
"c:\\windows\\microsoft.net\\framework*.dll",
"c:\\windows\\assembly\\nativeimages_*.ni.dll",
"c:\\windows\\winsxs\\temp\\pendingdeletes\\$$deleteme*",
"c:\\windows\\system32\\mrt\\*\\mpengine.dll",
"c:\\windows\\system32\\wbem\\fastprox.dll",
"c:\\windows\\winsxs\\*.dll",
"c:\\program files (x86)\\*",
"c:\\program files\\*",
"c:\\windows\\syswow64\\werfault.exe") and
not process.thread.Ext.call_stack_final_user_module.protection_provenance_path like
("c:\\windows\\microsoft.net\\framework*\\clr.dll",
"c:\\windows\\syswow64\\combase.dll",
"c:\\windows\\system32\\combase.dll") and
not (process.executable : "C:\\Windows\\ccmsetup\\cache\\ccmsetup.exe" and
process.parent.executable : ("C:\\Windows\\CCM\\CcmEval.exe", "C:\\Program Files\\SMS_CCM\\CcmEval.exe", "C:\\Windows\\CCM\\ccmrepair.exe")) and
not (process.Ext.api.name == "VirtualProtect" and
_arraysearch(process.thread.Ext.call_stack, $entry, $entry.symbol_info like ("c:\\windows\\sys?????\\ntdll.dll!LdrLoadDll*", "c:\\windows\\sys?????\\kernelbase.dll!LoadLibrary*"))) Field Validations
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