Sigma rule: Suspicious FromBase64String Usage On Gzip Archive - Ps Script

A detection rule from the SigmaHQ repository, shown as its author published it. Dataset version ref-6bd212ccf9fc, updated 2022-12-23T00:00:00.000Z.

Rule

Title
Suspicious FromBase64String Usage On Gzip Archive - Ps Script
Status
test
Level
medium
Author
frack113
Date
2022-12-23
File
rules/windows/powershell/powershell_script/posh_ps_frombase64string_archive.yml
Commit
ccbb0369507f796db0b0ae6854c8a2be471b9d84

Detects attempts of decoding a base64 Gzip archive in a PowerShell script. This technique is often used as a method to load malicious content into memory afterward.

Log source

product
windows
category
ps_script
definition
Requirements: Script Block Logging must be enabled

Detection

selection:
    ScriptBlockText|contains|all:
        - 'FromBase64String'
        - 'MemoryStream'
        - 'H4sI'
condition: selection

False positives (as the rule lists them)

  • Legitimate administrative script

Tags

  • attack.command-and-control
  • attack.t1132.001

MITRE ATT&CK ids this rule names

Related rules

References

Read on 2026-11-03T00:58:21.399Z under licence sigma-drl-1.1@d5f4c36a from https://github.com/SigmaHQ/sigma/blob/ccbb0369507f796db0b0ae6854c8a2be471b9d84/rules/windows/powershell/powershell_script/posh_ps_frombase64string_archive.yml

Sources and licences

  • SigmaHQ

    "Suspicious FromBase64String Usage On Gzip Archive - Ps Script" by frack113 (SigmaHQ). Rule: https://github.com/SigmaHQ/sigma/blob/ccbb0369507f796db0b0ae6854c8a2be471b9d84/rules/windows/powershell/powershell_script/posh_ps_frombase64string_archive.yml.
    Licensed under the Detection Rule License (DRL) 1.1: https://github.com/SigmaHQ/Detection-Rule-License

    Detection Rule License (DRL) 1.1

Cite this page

Dragons Eye Ransomware Tracker, "Sigma rule: Suspicious FromBase64String Usage On Gzip Archive - Ps Script",
entity page, dataset version ref-6bd212ccf9fc, updated 2022-12-23T00:00:00.000Z,
https://ransomware-tracker.com/detections/sigma/df69cb1d-b891-4cd9-90c7-d617d90100ce (accessed 2026-11-03).
Underlying source: SigmaHQ rule df69cb1d-b891-4cd9-90c7-d617d90100ce, commit ccbb0369507f796db0b0ae6854c8a2be471b9d84.

Pages change. The dataset version identifies the data, but no archive of old versions is kept, so this citation cannot be replayed later.