New Agent Skills Installation Attempt Via Node.EXE

Description

Detects the attempt to install new skills for AI agents using the "npx skills" command. Agent skills enhance AI agents with new capabilities, but attackers may abuse this mechanism to inject malicious commands executed by the agent on behalf of the user. The "npx skills" command can install skills for various agents (e.g., Claude Code, Cursor, and others). Analysts should review any installed skills to verify their legitimacy. Note: Tune this rule based on whether AI agent tooling is allowed in your environment. In environments where such tooling is authorized, this detection may reflect normal activity and the alert level should be adjusted accordingly. In environments where AI agent tooling is not permitted, this activity is likely suspicious and may require immediate investigation.

Query · sigma

selection_img:
- Image|endswith: \node.exe
- OriginalFileName: node.exe
selection_cli:
  CommandLine|contains|all:
  - npx-cli.js
  - 'skills '
  - ' add '
condition: all of selection_*

Known false positives

  • This rule will be triggered when a new agent skill is installed regardless if it is benign or malicious.
  • High false positive rate expected in environments where AI agent tooling is authorized and commonly used.
Raw source New Agent Skills Installation Attempt Via Node.EXE · Sigma
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Published by SigmaHQ/sigma ↗, licensed under Detection Rule License 1.1 ↗. Reproduced here unmodified. 
title: New Agent Skills Installation Attempt Via Node.EXE
id: afa71271-6a97-4e47-810f-83120fb1a4ce
status: experimental
description: |
    Detects the attempt to install new skills for AI agents using the "npx skills" command.
    Agent skills enhance AI agents with new capabilities, but attackers may abuse this mechanism to inject malicious commands executed by the agent on behalf of the user.
    The "npx skills" command can install skills for various agents (e.g., Claude Code, Cursor, and others).
    Analysts should review any installed skills to verify their legitimacy.
    Note: Tune this rule based on whether AI agent tooling is allowed in your environment.
    In environments where such tooling is authorized, this detection may reflect normal activity and the alert level should be adjusted accordingly.
    In environments where AI agent tooling is not permitted, this activity is likely suspicious and may require immediate investigation.
references:
    - https://blog.lukaszolejnik.com/supply-chain-risk-of-agentic-ai-infecting-infrastructures-via-skill-worms/
    - https://github.com/vercel-labs/skills/blob/1f7fbc8d0e49c4e0601d364696bd1bdd15e80967/README.md
    - https://opensourcemalware.com/blog/clawdbot-skills-ganked-your-crypto
    - https://promptintel.novahunting.ai/molt
author: Marco Pedrinazzi (@pedrinazziM) (InTheCyber)
date: 2026-02-03
tags:
    - attack.execution
    - attack.t1059.007
logsource:
    product: windows
    category: process_creation
detection:
    selection_img:
        - Image|endswith: '\node.exe'
        - OriginalFileName: 'node.exe'
    selection_cli:
        CommandLine|contains|all:
            - 'npx-cli.js'
            - 'skills '
            - ' add '
    condition: all of selection_*
falsepositives:
    - This rule will be triggered when a new agent skill is installed regardless if it is benign or malicious.
    - High false positive rate expected in environments where AI agent tooling is authorized and commonly used.
level: medium
regression_tests_path: regression_data/rules/windows/process_creation/proc_creation_win_node_new_agent_skills_installed/info.yml

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