Suspicious Curl File Upload - Linux — Sigma Rule

Rule metadata and linked tags

Author: Nasreddine Bencherchali (Nextron Systems), Cedric MAURUGEON (Update). Source status: test; severity: medium. Source dates: 2022-09-15 / 2023-05-02.

{
  "category": "process_creation",
  "product": "linux"
}

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: d4e05d83b666d4ee1066ac434304d8cca6963898ca6ac0731d5ec929a8589a1a

Detection logic

Original source YAML. Source-tag agreement is not proof of complete semantic coverage. This rule has not been compiled for a SIEM backend or validated against live telemetry here.

title: Suspicious Curl File Upload - Linux
id: 00b90cc1-17ec-402c-96ad-3a8117d7a582
related:
    - id: 00bca14a-df4e-4649-9054-3f2aa676bc04
      type: derived
status: test
description: Detects a suspicious curl process start the adds a file to a web request
references:
    - https://twitter.com/d1r4c/status/1279042657508081664
    - https://medium.com/@petehouston/upload-files-with-curl-93064dcccc76
    - https://github.com/redcanaryco/atomic-red-team/blob/f339e7da7d05f6057fdfcdd3742bfcf365fee2a9/atomics/T1105/T1105.md#atomic-test-19---curl-upload-file
    - https://curl.se/docs/manpage.html
    - https://www.trendmicro.com/en_us/research/22/i/how-malicious-actors-abuse-native-linux-tools-in-their-attacks.html
author: Nasreddine Bencherchali (Nextron Systems), Cedric MAURUGEON (Update)
date: 2022-09-15
modified: 2023-05-02
tags:
    - attack.exfiltration
    - attack.command-and-control
    - attack.t1567
    - attack.t1105
logsource:
    category: process_creation
    product: linux
detection:
    selection_img:
        Image|endswith: '/curl'
    selection_cli:
        - CommandLine|contains:
              - ' --form' # Also covers the "--form-string"
              - ' --upload-file '
              - ' --data '
              - ' --data-' # For flags like: "--data-ascii", "--data-binary", "--data-raw", "--data-urlencode"
        - CommandLine|re: '\s-[FTd]\s' # We use regex to ensure a case sensitive argument detection
    filter_optional_localhost:
        CommandLine|contains:
            - '://localhost'
            - '://127.0.0.1'
    condition: all of selection_* and not 1 of filter_optional_*
falsepositives:
    - Scripts created by developers and admins
level: medium

Original YAML and metadata in JSON

False positives

• Scripts created by developers and admins

Source references

• https://twitter.com/d1r4c/status/1279042657508081664
• https://medium.com/@petehouston/upload-files-with-curl-93064dcccc76
• https://github.com/redcanaryco/atomic-red-team/blob/f339e7da7d05f6057fdfcdd3742bfcf365fee2a9/atomics/T1105/T1105.md#atomic-test-19---curl-upload-file
• https://curl.se/docs/manpage.html
• https://www.trendmicro.com/en_us/research/22/i/how-malicious-actors-abuse-native-linux-tools-in-their-attacks.html