Sigma rule: Linux Base64 Encoded Shebang In CLI

Rule

Title

Linux Base64 Encoded Shebang In CLI

Status

test

Level

medium

Author

Nasreddine Bencherchali (Nextron Systems)

Date

2022-09-15

File

rules/linux/process_creation/proc_creation_lnx_base64_shebang_cli.yml

Commit

ccbb0369507f796db0b0ae6854c8a2be471b9d84

Detects the presence of a base64 version of the shebang in the commandline, which could indicate a malicious payload about to be decoded

Log source

product

linux

category

process_creation

Detection

selection:
    CommandLine|contains:
        - "IyEvYmluL2Jhc2" # Note: #!/bin/bash"
        - "IyEvYmluL2Rhc2" # Note: #!/bin/dash"
        - "IyEvYmluL3pza" # Note: #!/bin/zsh"
        - "IyEvYmluL2Zpc2" # Note: #!/bin/fish
        - "IyEvYmluL3No" # Note: # !/bin/sh"
condition: selection

False positives (as the rule lists them)

• Legitimate administration activities

Tags

• attack.stealth
• attack.t1140

MITRE ATT&CK ids this rule names

• T1140

References

• https://www.trendmicro.com/pl_pl/research/20/i/the-evolution-of-malicious-shell-scripts.html
• https://github.com/carlospolop/PEASS-ng/tree/master/linPEAS

Read on 2026-11-03T00:58:21.399Z under licence sigma-drl-1.1@d5f4c36a from https://github.com/SigmaHQ/sigma/blob/ccbb0369507f796db0b0ae6854c8a2be471b9d84/rules/linux/process_creation/proc_creation_lnx_base64_shebang_cli.yml