Home/CVE-2021-31957/Sigma rules
Sigma

Sigma rules for CVE-2021-31957

6 rules · scoped to cve · back to CVE-2021-31957
Direct rules mention this entity in their title or description. Related rules cover the techniques this entity is known to use.
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Detection rules

6 of 6
direct high
UAC Bypass Using .NET Code Profiler on MMC
Detects the pattern of UAC Bypass using .NET Code Profiler and mmc.exe DLL hijacking (UACMe 39)
status test author Christian Burkard (Nextron Systems) id 93a19907-d4f9-4deb-9f91-aac4692776a6 license Sigma · DRL-1.1
view Sigma YAML 
title: UAC Bypass Using .NET Code Profiler on MMC
id: 93a19907-d4f9-4deb-9f91-aac4692776a6
status: test
description: Detects the pattern of UAC Bypass using .NET Code Profiler and mmc.exe DLL hijacking (UACMe 39)
references:
    - https://github.com/hfiref0x/UACME
author: Christian Burkard (Nextron Systems)
date: 2021-08-30
modified: 2022-10-09
tags:
    - attack.privilege-escalation
    - attack.t1548.002
logsource:
    category: file_event
    product: windows
detection:
    selection:
        TargetFilename|startswith: 'C:\Users\'
        TargetFilename|endswith: '\AppData\Local\Temp\pe386.dll'
    condition: selection
falsepositives:
    - Unknown
level: high
direct high
Potential AMSI Bypass Via .NET Reflection
Detects Request to "amsiInitFailed" that can be used to disable AMSI Scanning
status test author Markus Neis, @Kostastsale id 30edb182-aa75-42c0-b0a9-e998bb29067c license Sigma · DRL-1.1
view Sigma YAML 
title: Potential AMSI Bypass Via .NET Reflection
id: 30edb182-aa75-42c0-b0a9-e998bb29067c
related:
    - id: 4f927692-68b5-4267-871b-073c45f4f6fe
      type: obsolete
status: test
description: Detects Request to "amsiInitFailed" that can be used to disable AMSI Scanning
references:
    - https://s3cur3th1ssh1t.github.io/Bypass_AMSI_by_manual_modification/
    - https://www.mdsec.co.uk/2018/06/exploring-powershell-amsi-and-logging-evasion/
author: Markus Neis, @Kostastsale
date: 2018-08-17
modified: 2023-02-03
tags:
    - attack.defense-impairment
    - attack.t1685
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        - CommandLine|contains|all:
              - 'System.Management.Automation.AmsiUtils'
              - 'amsiInitFailed'
        - CommandLine|contains|all:
              - '[Ref].Assembly.GetType'
              - 'SetValue($null,$true)'
              - 'NonPublic,Static'
    condition: selection
falsepositives:
    - Unlikely
level: high
direct high
ETW Logging Tamper In .NET Processes Via CommandLine
Detects changes to environment variables related to ETW logging via the CommandLine. This could indicate potential adversaries stopping ETW providers recording loaded .NET assemblies.
status test author Roberto Rodriguez (Cyb3rWard0g), OTR (Open Threat Research) id 41421f44-58f9-455d-838a-c398859841d4 license Sigma · DRL-1.1
view Sigma YAML 
title: ETW Logging Tamper In .NET Processes Via CommandLine
id: 41421f44-58f9-455d-838a-c398859841d4
status: test
description: |
    Detects changes to environment variables related to ETW logging via the CommandLine.
    This could indicate potential adversaries stopping ETW providers recording loaded .NET assemblies.
references:
    - https://twitter.com/_xpn_/status/1268712093928378368
    - https://social.msdn.microsoft.com/Forums/vstudio/en-US/0878832e-39d7-4eaf-8e16-a729c4c40975/what-can-i-use-e13c0d23ccbc4e12931bd9cc2eee27e4-for?forum=clr
    - https://github.com/dotnet/runtime/blob/ee2355c801d892f2894b0f7b14a20e6cc50e0e54/docs/design/coreclr/jit/viewing-jit-dumps.md#setting-configuration-variables
    - https://github.com/dotnet/runtime/blob/f62e93416a1799aecc6b0947adad55a0d9870732/src/coreclr/src/inc/clrconfigvalues.h#L35-L38
    - https://github.com/dotnet/runtime/blob/7abe42dc1123722ed385218268bb9fe04556e3d3/src/coreclr/src/inc/clrconfig.h#L33-L39
    - https://github.com/dotnet/runtime/search?p=1&q=COMPlus_&unscoped_q=COMPlus_
    - https://bunnyinside.com/?term=f71e8cb9c76a
    - http://managed670.rssing.com/chan-5590147/all_p1.html
    - https://github.com/dotnet/runtime/blob/4f9ae42d861fcb4be2fcd5d3d55d5f227d30e723/docs/coding-guidelines/clr-jit-coding-conventions.md#1412-disabling-code
    - https://i.blackhat.com/EU-21/Wednesday/EU-21-Teodorescu-Veni-No-Vidi-No-Vici-Attacks-On-ETW-Blind-EDRs.pdf
author: Roberto Rodriguez (Cyb3rWard0g), OTR (Open Threat Research)
date: 2020-05-02
modified: 2022-12-09
tags:
    - attack.defense-impairment
    - attack.t1685
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        CommandLine|contains:
            - 'COMPlus_ETWEnabled'
            - 'COMPlus_ETWFlags'
    condition: selection
falsepositives:
    - Unlikely
level: high
direct high
ETW Logging Disabled In .NET Processes - Registry
Potential adversaries stopping ETW providers recording loaded .NET assemblies.
status test author Roberto Rodriguez (Cyb3rWard0g), OTR (Open Threat Research) id a4c90ea1-2634-4ca0-adbb-35eae169b6fc license Sigma · DRL-1.1
view Sigma YAML 
title: ETW Logging Disabled In .NET Processes - Registry
id: a4c90ea1-2634-4ca0-adbb-35eae169b6fc
related:
    - id: bf4fc428-dcc3-4bbd-99fe-2422aeee2544
      type: similar
status: test
description: Potential adversaries stopping ETW providers recording loaded .NET assemblies.
references:
    - https://twitter.com/_xpn_/status/1268712093928378368
    - https://social.msdn.microsoft.com/Forums/vstudio/en-US/0878832e-39d7-4eaf-8e16-a729c4c40975/what-can-i-use-e13c0d23ccbc4e12931bd9cc2eee27e4-for?forum=clr
    - https://github.com/dotnet/runtime/blob/ee2355c801d892f2894b0f7b14a20e6cc50e0e54/docs/design/coreclr/jit/viewing-jit-dumps.md#setting-configuration-variables
    - https://github.com/dotnet/runtime/blob/f62e93416a1799aecc6b0947adad55a0d9870732/src/coreclr/src/inc/clrconfigvalues.h#L35-L38
    - https://github.com/dotnet/runtime/blob/7abe42dc1123722ed385218268bb9fe04556e3d3/src/coreclr/src/inc/clrconfig.h#L33-L39
    - https://github.com/dotnet/runtime/search?p=1&q=COMPlus_&unscoped_q=COMPlus_
    - https://bunnyinside.com/?term=f71e8cb9c76a
    - http://managed670.rssing.com/chan-5590147/all_p1.html
    - https://github.com/dotnet/runtime/blob/4f9ae42d861fcb4be2fcd5d3d55d5f227d30e723/docs/coding-guidelines/clr-jit-coding-conventions.md#1412-disabling-code
    - https://i.blackhat.com/EU-21/Wednesday/EU-21-Teodorescu-Veni-No-Vidi-No-Vici-Attacks-On-ETW-Blind-EDRs.pdf
author: Roberto Rodriguez (Cyb3rWard0g), OTR (Open Threat Research)
date: 2020-06-05
modified: 2022-12-20
tags:
    - attack.persistence
    - attack.defense-impairment
    - attack.t1112
    - attack.t1685
logsource:
    product: windows
    service: security
detection:
    selection_etw_enabled:
        EventID: 4657
        ObjectName|endswith: '\SOFTWARE\Microsoft\.NETFramework'
        ObjectValueName: 'ETWEnabled'
        NewValue: 0
    selection_complus:
        EventID: 4657
        ObjectName|contains: '\Environment'
        ObjectValueName:
            - 'COMPlus_ETWEnabled'
            - 'COMPlus_ETWFlags'
        NewValue: 0
    condition: 1 of selection_*
falsepositives:
    - Unknown
level: high
direct high
ETW Logging Disabled In .NET Processes - Sysmon Registry
Potential adversaries stopping ETW providers recording loaded .NET assemblies.
status test author Roberto Rodriguez (Cyb3rWard0g), OTR (Open Threat Research) id bf4fc428-dcc3-4bbd-99fe-2422aeee2544 license Sigma · DRL-1.1
view Sigma YAML 
title: ETW Logging Disabled In .NET Processes - Sysmon Registry
id: bf4fc428-dcc3-4bbd-99fe-2422aeee2544
related:
    - id: a4c90ea1-2634-4ca0-adbb-35eae169b6fc
      type: similar
status: test
description: Potential adversaries stopping ETW providers recording loaded .NET assemblies.
references:
    - https://twitter.com/_xpn_/status/1268712093928378368
    - https://social.msdn.microsoft.com/Forums/vstudio/en-US/0878832e-39d7-4eaf-8e16-a729c4c40975/what-can-i-use-e13c0d23ccbc4e12931bd9cc2eee27e4-for?forum=clr
    - https://github.com/dotnet/runtime/blob/ee2355c801d892f2894b0f7b14a20e6cc50e0e54/docs/design/coreclr/jit/viewing-jit-dumps.md#setting-configuration-variables
    - https://github.com/dotnet/runtime/blob/f62e93416a1799aecc6b0947adad55a0d9870732/src/coreclr/src/inc/clrconfigvalues.h#L35-L38
    - https://github.com/dotnet/runtime/blob/7abe42dc1123722ed385218268bb9fe04556e3d3/src/coreclr/src/inc/clrconfig.h#L33-L39
    - https://github.com/dotnet/runtime/search?p=1&q=COMPlus_&unscoped_q=COMPlus_
    - https://bunnyinside.com/?term=f71e8cb9c76a
    - http://managed670.rssing.com/chan-5590147/all_p1.html
    - https://github.com/dotnet/runtime/blob/4f9ae42d861fcb4be2fcd5d3d55d5f227d30e723/docs/coding-guidelines/clr-jit-coding-conventions.md#1412-disabling-code
    - https://blog.xpnsec.com/hiding-your-dotnet-complus-etwenabled/
    - https://i.blackhat.com/EU-21/Wednesday/EU-21-Teodorescu-Veni-No-Vidi-No-Vici-Attacks-On-ETW-Blind-EDRs.pdf
author: Roberto Rodriguez (Cyb3rWard0g), OTR (Open Threat Research)
date: 2020-06-05
modified: 2023-08-17
tags:
    - attack.persistence
    - attack.defense-impairment
    - attack.t1112
    - attack.t1685
logsource:
    product: windows
    category: registry_set
detection:
    selection_etw_enabled:
        TargetObject|endswith: 'SOFTWARE\Microsoft\.NETFramework\ETWEnabled'
        Details: 'DWORD (0x00000000)'
    selection_complus:
        TargetObject|endswith:
            - '\COMPlus_ETWEnabled'
            - '\COMPlus_ETWFlags'
        Details:
            - 0 # For REG_SZ type
            - 'DWORD (0x00000000)'
    condition: 1 of selection_*
falsepositives:
    - Unknown
level: high
direct medium
Dynamic .NET Compilation Via Csc.EXE
Detects execution of "csc.exe" to compile .NET code. Attackers often leverage this to compile code on the fly and use it in other stages.
status test author Florian Roth (Nextron Systems), X__Junior (Nextron Systems) id dcaa3f04-70c3-427a-80b4-b870d73c94c4 license Sigma · DRL-1.1
view Sigma YAML 
title: Dynamic .NET Compilation Via Csc.EXE
id: dcaa3f04-70c3-427a-80b4-b870d73c94c4
status: test
description: Detects execution of "csc.exe" to compile .NET code. Attackers often leverage this to compile code on the fly and use it in other stages.
references:
    - https://securityboulevard.com/2019/08/agent-tesla-evading-edr-by-removing-api-hooks/
    - https://www.clearskysec.com/wp-content/uploads/2018/11/MuddyWater-Operations-in-Lebanon-and-Oman.pdf
    - https://app.any.run/tasks/c6993447-d1d8-414e-b856-675325e5aa09/
    - https://twitter.com/gN3mes1s/status/1206874118282448897
    - https://github.com/redcanaryco/atomic-red-team/blob/b27a3cb25025161d49ac861cb216db68c46a3537/atomics/T1027.004/T1027.004.md#atomic-test-1---compile-after-delivery-using-cscexe
author: Florian Roth (Nextron Systems), X__Junior (Nextron Systems)
date: 2019-08-24
modified: 2026-03-23
tags:
    - attack.stealth
    - attack.t1027.004
logsource:
    category: process_creation
    product: windows
detection:
    selection_img:
        Image|endswith: '\csc.exe'
    selection_susp_location_1:
        CommandLine|contains:
            - ':\Perflogs\'
            - ':\Users\Public\'
            - '\AppData\Local\Temp\' # User execution
            - '\Temporary Internet'
            - '\Windows\Temp\' # Admin execution
    selection_susp_location_2:
        - CommandLine|contains|all:
              - ':\Users\'
              - '\Favorites\'
        - CommandLine|contains|all:
              - ':\Users\'
              - '\Favourites\'
        - CommandLine|contains|all:
              - ':\Users\'
              - '\Contacts\'
        - CommandLine|contains|all:
              - ':\Users\'
              - '\Pictures\'
    selection_susp_location_3:
        CommandLine|re: '(?:[Pp]rogram[Dd]ata|%(?:[Ll]ocal)?[Aa]pp[Dd]ata%|\\[Aa]pp[Dd]ata\\(?:[Ll]ocal(?:[Ll]ow)?|[Rr]oaming))\\[^\\]{1,256}$'
    filter_main_programfiles:
        # Note: this is a generic filter. You could baseline execution in your env for a more robust rule
        ParentImage|startswith:
            - 'C:\Program Files (x86)\' # https://twitter.com/gN3mes1s/status/1206874118282448897
            - 'C:\Program Files\' # https://twitter.com/gN3mes1s/status/1206874118282448897
    filter_main_sdiagnhost:
        ParentImage: 'C:\Windows\System32\sdiagnhost.exe' # https://twitter.com/gN3mes1s/status/1206874118282448897
    filter_main_w3p:
        ParentImage: 'C:\Windows\System32\inetsrv\w3wp.exe' # https://twitter.com/gabriele_pippi/status/1206907900268072962
    filter_optional_chocolatey:
        ParentImage: # Chocolatey https://chocolatey.org/
            - 'C:\ProgramData\chocolatey\choco.exe'
            - 'C:\ProgramData\chocolatey\tools\shimgen.exe'
    filter_optional_defender:
        ParentCommandLine|contains: '\ProgramData\Microsoft\Windows Defender Advanced Threat Protection'
    filter_optional_ansible:
        # Note: As ansible is widely used we exclude it with this generic filter.
        # A better option would be to filter based on script content basis or other marker while hunting
        ParentCommandLine|contains:
            # '{"failed":true,"msg":"Ansible requires PowerShell v3.0 or newer"}'
            - 'JwB7ACIAZgBhAGkAbABlAGQAIgA6AHQAcgB1AGUALAAiAG0AcwBnACIAOgAiAEEAbgBzAGkAYgBsAGUAIAByAGUAcQB1AGkAcgBlAHMAIABQAG8AdwBlAHIAUwBoAGUAbABsACAAdgAzAC4AMAAgAG8AcgAgAG4AZQB3AGUAcgAiAH0AJw'
            - 'cAewAiAGYAYQBpAGwAZQBkACIAOgB0AHIAdQBlACwAIgBtAHMAZwAiADoAIgBBAG4AcwBpAGIAbABlACAAcgBlAHEAdQBpAHIAZQBzACAAUABvAHcAZQByAFMAaABlAGwAbAAgAHYAMwAuADAAIABvAHIAIABuAGUAdwBlAHIAIgB9ACcA'
            - 'nAHsAIgBmAGEAaQBsAGUAZAAiADoAdAByAHUAZQAsACIAbQBzAGcAIgA6ACIAQQBuAHMAaQBiAGwAZQAgAHIAZQBxAHUAaQByAGUAcwAgAFAAbwB3AGUAcgBTAGgAZQBsAGwAIAB2ADMALgAwACAAbwByACAAbgBlAHcAZQByACIAfQAnA'
    condition: selection_img and 1 of selection_susp_location_* and not 1 of filter_main_* and not 1 of filter_optional_*
falsepositives:
    - Legitimate software from program files - https://twitter.com/gN3mes1s/status/1206874118282448897
    - Legitimate Microsoft software - https://twitter.com/gabriele_pippi/status/1206907900268072962
    - Ansible
level: medium
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