Query: Sigma rule for Detects base64 encoded strings used in hidden malicious PowerShell command lines
Matching passage: Sigma rule: Detects base64 encoded strings used in hidden malicious PowerShell command lines. Logsource: windows / process_creation. Rule: title: Malicious Base64 Encoded PowerShell Keywords in Command Lines id: f26c6093-6f14-4b12-800f-0fcb46f5ffd0 status: test description: Detects base64 encoded strings used in hidden malicious PowerShell command lines references: - http://www.leeholmes.com/blog/2017/09/21/searching-for-content-in-base-64-strings/ author: John Lambert (rule) date: 2019-01-16 modified: 2023-01-05 tags: - attack.execution - attack.t1059.001 logsource: category: process_creation product: windows detection: selection_img: - Image|endswith: - \powershell.exe - \pwsh.exe - OriginalFileName: - PowerShell.EXE - pwsh.dll selection_hidden: CommandLine|contains: ' hidden ' selection_encoded: CommandLine|contains: - AGkAdABzAGEAZABtAGkAbgAgAC8AdAByAGEAbgBzAGYAZQByA - aXRzYWRtaW4gL3RyYW5zZmVy - IAaQB0AHMAYQBkAG0AaQBuACAALwB0AHIAYQBuAHMAZgBlAHIA - JpdHNhZG1pbiAvdHJhbnNmZX - YgBpAHQAcwBhAGQAbQBpAG4AIAAvAHQAcgBhAG4AcwBmAGUAcg - Yml0c2FkbWluIC90cmFuc2Zlc - AGMAaAB1AG4AawBfAHMAaQB6AGUA - JABjAGgAdQBuAGsAXwBzAGkAegBlA - JGNodW5rX3Npem - QAYwBoAHUAbgBrAF8AcwBpAHoAZQ - RjaHVua19zaXpl - Y2h1bmtfc2l6Z - AE8ALgBDAG8AbQBwAHIAZQBzAHMAaQBvAG4A - kATwAuAEMAbwBtAHAAcgBlAHMAcwBpAG8Abg - lPLkNvbXByZXNzaW9u - SQBPAC4AQwBvAG0AcAByAGUAcwBzAGkAbwBuA - SU8uQ29tcHJlc3Npb2 - Ty5Db21wcmVzc2lvb - AE8ALgBNAGUAbQBvAHIAeQBTAHQAcgBlAGEAbQ - kATwAuAE0AZQBtAG8AcgB5AFMAdAByAGUAYQBtA - lPLk1lbW9yeVN0cmVhb - SQBPAC4ATQBlAG0AbwByAHkAUwB0AHIAZQBhAG0A - SU8uTWVtb3J5U3RyZWFt - Ty5NZW1vcnlTdHJlYW - 4ARwBlAHQAQwBoAHUAbgBrA - 5HZXRDaHVua - AEcAZQB0AEMAaAB1AG4Aaw - LgBHAGUAdABDAGgAdQBuAGsA - LkdldENodW5r - R2V0Q2h1bm - AEgAUgBFAEEARABfAEkATgBGAE8ANgA0A - QASABSAEUAQQBEAF8ASQBOAEYATwA2ADQA - RIUkVBRF9JTkZPNj - SFJFQURfSU5GTzY0 - VABIAFIARQBBAEQAXwBJAE4ARgBPADYANA - VEhSRUFEX0lORk82N - AHIAZQBhAHQAZQBSAGUAbQBvAHQAZQBUAGgAcgBlAGEAZA - cmVhdGVSZW1vdGVUaHJlYW - MAcgBlAGEAdABlAFIAZQBtAG8AdABlAFQAaAByAGUAYQBkA - NyZWF0ZVJlbW90ZVRocmVhZ - Q3JlYXRlUmVtb3RlVGhyZWFk - QwByAGUAYQB0AGUAUgBlAG0AbwB0AGUAVABoAHIAZQBhAGQA - 0AZQBtAG0AbwB2AGUA - 1lbW1vdm - AGUAbQBtAG8AdgBlA - bQBlAG0AbQBvAHYAZQ - bWVtbW92Z - ZW1tb3Zl condition: all of selection_* falsepositives: - Unknown level: high
Near-miss passage: Sigma rule: Detects changes to the NGenAssemblyUsageLog registry key. .NET Usage Log output location can be controlled by setting th. Logsource: windows / registry_set. Rule: title: NET NGenAssemblyUsageLog Registry Key Tamper id: 28036918-04d3-423d-91c0-55ecf99fb892 status: test description: 'Detects changes to the NGenAssemblyUsageLog registry key. .NET Usage Log output location can be controlled by setting the NGenAssemblyUsageLog CLR configuration knob in the Registry or by configuring an environment variable (as described in the next section). By simplify specifying an arbitrary value (e.g. fake output location or junk data) for the expected value, a Usage Log file for the .NET execution context will not be created. ' references: - https://bohops.com/2021/03/16/investigating-net-clr-usage-log-tampering-techniques-for-edr-evasion/ author: frack113 date: 2022-11-18 modified: 2023-08-17 tags: - attack.persistence - attack.defense-impairment - attack.t1112 logsource: product: windows category: registry_set detection: selection: TargetObject|endswith: SOFTWARE\Microsoft\.NETFramework\NGenAssemblyUsageLog condition: selection falsepositives: - Unknown level: high