{"id":"fa2559c8-1197-471d-9cdd-05a0273d4522","title":"Potential AMSI Bypass Script Using NULL Bits","description":"Detects usage of special strings/null bits in order to potentially bypass AMSI functionalities","author":"Nasreddine Bencherchali (Nextron Systems)","status":"test","level":"medium","date":"2023-01-04","modified":"2023-05-09","tags":["attack.defense-impairment","attack.t1685"],"technique_ids":["T1685"],"logsource":{"product":"windows","category":"ps_script","definition":"Requirements: Script Block Logging must be enabled"},"falsepositives":["Unknown"],"references":["https://github.com/r00t-3xp10it/hacking-material-books/blob/43cb1e1932c16ff1f58b755bc9ab6b096046853f/obfuscation/simple_obfuscation.md#amsi-bypass-using-null-bits-satoshi"],"source_path":"rules/windows/powershell/powershell_script/posh_ps_amsi_null_bits_bypass.yml","source_sha256":"00e5953d97cf9c2c349f2421a6b8073cc2ae356e25df46305a4e50b3b6df8eb6","source_url":"https://github.com/anpa1200/sigma/blob/b249e9683190cffdcaf188ccbfb90bf4759844e1/rules/windows/powershell/powershell_script/posh_ps_amsi_null_bits_bypass.yml","license":"Detection Rule License 1.1","license_url":"https://github.com/SigmaHQ/Detection-Rule-License/blob/main/LICENSE.Detection.Rules.md","yaml":"title: Potential AMSI Bypass Script Using NULL Bits\nid: fa2559c8-1197-471d-9cdd-05a0273d4522\nrelated:\n    - id: 92a974db-ab84-457f-9ec0-55db83d7a825\n      type: similar\nstatus: test\ndescription: Detects usage of special strings/null bits in order to potentially bypass AMSI functionalities\nreferences:\n    - https://github.com/r00t-3xp10it/hacking-material-books/blob/43cb1e1932c16ff1f58b755bc9ab6b096046853f/obfuscation/simple_obfuscation.md#amsi-bypass-using-null-bits-satoshi\nauthor: Nasreddine Bencherchali (Nextron Systems)\ndate: 2023-01-04\nmodified: 2023-05-09\ntags:\n    - attack.defense-impairment\n    - attack.t1685\nlogsource:\n    product: windows\n    category: ps_script\n    definition: 'Requirements: Script Block Logging must be enabled'\ndetection:\n    selection:\n        ScriptBlockText|contains:\n            - \"if(0){{{0}}}' -f $(0 -as [char]) +\"\n            - \"#<NULL>\"\n    condition: selection\nfalsepositives:\n    - Unknown\nlevel: medium\n","validation":"yaml_parsed_not_backend_compiled_or_live_validated","techniques":[{"key":"enterprise/T1685","id":"T1685","name":"Disable or Modify Tools","page":"techniques/enterprise/T1685/"}],"data_path":"data/detection-rules/fa2559c8-1197-471d-9cdd-05a0273d4522.json","kind":"sigma"}