diff --git a/rules-threat-hunting/windows/process_creation/proc_creation_win_regsvr32_dllregisterserver_exec.yml b/rules-threat-hunting/windows/process_creation/proc_creation_win_regsvr32_dllregisterserver_exec.yml new file mode 100644 index 000000000..12abe2b93 --- /dev/null +++ b/rules-threat-hunting/windows/process_creation/proc_creation_win_regsvr32_dllregisterserver_exec.yml @@ -0,0 +1,54 @@ +title: Regsvr32.EXE Calling of DllRegisterServer Export Function Implicitly +id: ce2c44b5-a6ac-412a-afba-9e89326fa972 +related: + - id: 0ba1da6d-b6ce-4366-828c-18826c9de23e + type: similar +status: experimental +description: | + Detects execution of regsvr32 with the silent flag and no other flags on a DLL located in an uncommon or potentially suspicious location. + When Regsvr32 is called in such a way, it implicitly calls the DLL export function 'DllRegisterServer'. +references: + - https://thedfirreport.com/2023/08/28/html-smuggling-leads-to-domain-wide-ransomware/ + - https://www.virustotal.com/gui/file/288fc4f954f98d724e6fab32a89477943df5c0e9662cb199a19b90ae0c63aebe/detection + - https://learn.microsoft.com/en-us/windows/win32/api/olectl/nf-olectl-dllregisterserver + - https://ss64.com/nt/regsvr32.html +author: Andreas Braathen (mnemonic.io), Nasreddine Bencherchali (Nextron Systems) +date: 2023/10/17 +tags: + - attack.execution + - attack.t1218 + - detection.threat_hunting +logsource: + category: process_creation + product: windows +detection: + selection_image: + - Image|endswith: '\regsvr32.exe' + - OriginalFileName: 'REGSVR32.EXE' + selection_cmdline: + CommandLine|contains: + - ' /s ' + - ' /e ' + filter_main_paths: + - CommandLine|contains: + - ':\Program Files (x86)' + - ':\Program Files\' + - ':\Windows\System32\' + - ':\Windows\SysWOW64\' + - CurrentDirectory|contains: + - ':\Program Files (x86)' + - ':\Program Files\' + - ':\Windows\System32\' + - ':\Windows\SysWOW64\' + filter_main_other_flags: + # Note: We filter other flags to keep the logic of the rule + CommandLine|contains: + - ' /i:' + - '/U ' + filter_main_rpcproxy: + ParentCommandLine|endswith: ':\Windows\System32\RpcProxy\RpcProxy.dll' + CommandLine: 'regsvr32 /s rpcproxy.dll' + condition: all of selection_* and not 1 of filter_main_* +falsepositives: + - Legitimate usage as part of application installation, but less likely from e.g. temporary paths. +level: medium diff --git a/rules-threat-hunting/windows/process_creation/proc_creation_win_rundll32_dllregisterserver.yml b/rules-threat-hunting/windows/process_creation/proc_creation_win_rundll32_dllregisterserver.yml new file mode 100644 index 000000000..32deeb8eb --- /dev/null +++ b/rules-threat-hunting/windows/process_creation/proc_creation_win_rundll32_dllregisterserver.yml @@ -0,0 +1,38 @@ +title: Rundll32.EXE Calling DllRegisterServer Export Function Explicitly +id: d81a9fc6-55db-4461-b962-0e78fea5b0ad +related: + - id: 2569ed8c-1147-498a-9b8c-2ad3656b10ed # Renamed rundll32 + type: similar +status: experimental +description: | + Detects when the DLL export function 'DllRegisterServer' is called in the commandline by Rundll32 explicitly where the DLL is located in a non-standard path. +references: + - https://thedfirreport.com/2023/08/28/html-smuggling-leads-to-domain-wide-ransomware/ + - https://www.virustotal.com/gui/file/94816439312563db982cd038cf77cbc5ef4c7003e3edee86e2b0f99e675ed4ed/behavior + - https://learn.microsoft.com/en-us/windows/win32/api/olectl/nf-olectl-dllregisterserver +author: Andreas Braathen (mnemonic.io) +date: 2023/10/17 +tags: + - attack.execution + - attack.t1218 + - detection.threat_hunting +logsource: + category: process_creation + product: windows +detection: + selection_image: + - Image|endswith: '\rundll32.exe' + - OriginalFileName: 'RUNDLL32.EXE' + selection_cmdline: + CommandLine|contains: 'DllRegisterServer' + filter_main_legit_paths: + CommandLine|contains: + - ':\Program Files (x86)' + - ':\Program Files\' + - ':\Windows\System32\' + - ':\Windows\SysWOW64\' + condition: all of selection_* and not 1 of filter_main_* +falsepositives: + - Legitimate usage as part of application installation, but less likely from e.g. temporary paths. + - Not every instance is considered malicious, but this rule will capture the malicious usages. +level: medium