Suspicious Curl.EXE Download — Sigma Rule

Rule metadata and linked tags

Author: Florian Roth (Nextron Systems), Nasreddine Bencherchali (Nextron Systems). Source status: test; severity: high. Source dates: 2020-07-03 / 2023-02-21.

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

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: 6488ac193d6c1369f4efc7de10113e6b272db296abe3bae0dc5bd5285cd0eed8

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.EXE Download
id: e218595b-bbe7-4ee5-8a96-f32a24ad3468
related:
    - id: bbeaed61-1990-4773-bf57-b81dbad7db2d # Basic curl execution
      type: derived
    - id: 9a517fca-4ba3-4629-9278-a68694697b81 # Curl download
      type: similar
status: test
description: Detects a suspicious curl process start on Windows and outputs the requested document to a local file
references:
    - https://twitter.com/max_mal_/status/1542461200797163522
    - https://web.archive.org/web/20200128160046/https://twitter.com/reegun21/status/1222093798009790464
    - https://github.com/pr0xylife/Qakbot/blob/4f0795d79dabee5bc9dd69f17a626b48852e7869/Qakbot_AA_23.06.2022.txt
    - https://www.volexity.com/blog/2022/07/28/sharptongue-deploys-clever-mail-stealing-browser-extension-sharpext/
    - https://github.com/redcanaryco/atomic-red-team/blob/0f229c0e42bfe7ca736a14023836d65baa941ed2/atomics/T1105/T1105.md#atomic-test-18---curl-download-file
author: Florian Roth (Nextron Systems), Nasreddine Bencherchali (Nextron Systems)
date: 2020-07-03
modified: 2023-02-21
tags:
    - attack.command-and-control
    - attack.t1105
logsource:
    category: process_creation
    product: windows
detection:
    selection_curl:
        - Image|endswith: '\curl.exe'
        - Product: 'The curl executable'
    selection_susp_locations:
        CommandLine|contains:
            - '%AppData%'
            - '%Public%'
            - '%Temp%'
            - '%tmp%'
            - '\AppData\'
            - '\Desktop\'
            - '\Temp\'
            - '\Users\Public\'
            - 'C:\PerfLogs\'
            - 'C:\ProgramData\'
            - 'C:\Windows\Temp\'
    selection_susp_extensions:
        CommandLine|endswith:
            - '.dll'
            - '.gif'
            - '.jpeg'
            - '.jpg'
            - '.png'
            - '.temp'
            - '.tmp'
            - '.txt'
            - '.vbe'
            - '.vbs'
    filter_optional_git_windows:
        # Example FP
        #   CommandLine: "C:\Program Files\Git\mingw64\bin\curl.exe" --silent --show-error --output C:/Users/test/AppData/Local/Temp/gfw-httpget-jVOEoxbS.txt --write-out %{http_code} https://gitforwindows.org/latest-tag.txt
        ParentImage: 'C:\Program Files\Git\usr\bin\sh.exe'
        Image: 'C:\Program Files\Git\mingw64\bin\curl.exe'
        CommandLine|contains|all:
            - '--silent --show-error --output '
            - 'gfw-httpget-'
            - 'AppData'
    condition: selection_curl and 1 of selection_susp_* and not 1 of filter_optional_*
falsepositives:
    - Unknown
level: high
regression_tests_path: regression_data/rules/windows/process_creation/proc_creation_win_curl_susp_download/info.yml
simulation:
    - type: atomic-red-team
      name: Curl Download File
      technique: T1105
      atomic_guid: 2b080b99-0deb-4d51-af0f-833d37c4ca6a

Original YAML and metadata in JSON

False positives

• Unknown

Source references

• https://twitter.com/max_mal_/status/1542461200797163522
• https://web.archive.org/web/20200128160046/https://twitter.com/reegun21/status/1222093798009790464
• https://github.com/pr0xylife/Qakbot/blob/4f0795d79dabee5bc9dd69f17a626b48852e7869/Qakbot_AA_23.06.2022.txt
• https://www.volexity.com/blog/2022/07/28/sharptongue-deploys-clever-mail-stealing-browser-extension-sharpext/
• https://github.com/redcanaryco/atomic-red-team/blob/0f229c0e42bfe7ca736a14023836d65baa941ed2/atomics/T1105/T1105.md#atomic-test-18---curl-download-file