Linux Base64 Utility Decoding with -d/--decode in Process Creation

Identifies Linux base64 decoding activity using base64 with the -d/--decode flag.

FreeReviewedSigma · Low · v3

Product: linux
Category: process_creation
Author: Daniil Yugoslavskiy, oscd.community (SigmaHQ), DRL 1.1
Published: 2020-10-19
Updated: 2026-07-31

ATT&CK techniques

Defense Evasion

Recon
Resource Dev
Initial Access
Execution
Persistence
Priv Esc
Defense Evasion
- T1027Obfuscated Files or Information
Cred Access
Discovery
Lateral Movement
Collection
C2
Exfiltration
Impact

What it detects

Identifies process executions of the base64 utility on Linux where the command line includes decode flags (-d or --decode). Attackers may use base64 decoding to reconstruct or stage data that is initially encoded to evade simple inspection. The rule relies on process creation telemetry, matching the executable path ending in /base64 and the presence of decode options in the command line.

Reporting behind it

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Linux Base64 Utility Decoding with -d/--decode in Process Creation

Pivot detection · T1027 · 9 related

Changelog

v3
Candidate ingested via manual entry.2026-07-31
v2
Candidate ingested via manual entry.2026-07-31
v1
No changelog recorded for this version.2026-07-30

Detection content is published as a reviewed draft. Tune thresholds and exclusions against your own telemetry before enabling this rule for alerting.

linux-base64-utility-decoding-via-base64-d-command-line-e2072cab

title: Linux Base64 Utility Decoding with -d/--decode in Process Creation
id: 084fd3dc-2248-4df7-9124-118626c8b59d
status: test
description: Identifies process executions of the base64 utility on Linux where the command line includes decode flags (-d or --decode). Attackers may use base64 decoding to reconstruct or stage data that is initially encoded to evade simple inspection. The rule relies on process creation telemetry, matching the executable path ending in /base64 and the presence of decode options in the command line.
references:
  - https://github.com/redcanaryco/atomic-red-team/blob/f339e7da7d05f6057fdfcdd3742bfcf365fee2a9/atomics/T1027/T1027.md
  - https://github.com/SigmaHQ/sigma/blob/master/rules/linux/process_creation/proc_creation_lnx_base64_decode.yml
author: Daniil Yugoslavskiy, oscd.community, Huntrule Team
date: 2020-10-19
modified: 2021-11-27
tags:
  - attack.stealth
  - attack.t1027
logsource:
  category: process_creation
  product: linux
detection:
  selection:
    Image|endswith: /base64
    CommandLine|contains: -d
  condition: selection
falsepositives:
  - Legitimate activities
level: low
license: DRL-1.1
related:
  - id: e2072cab-8c9a-459b-b63c-40ae79e27031
    type: derived

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