Shai-Hulud Malicious Bun Execution

Status: experimental
Severity: high
Log source: category process_creation, product windows
Author: Swachchhanda Shrawan Poudel (Nextron Systems)
Source: github.com/SigmaHQ/sigma

Detects the execution of bun_environment.js via the Bun runtime, a behavior associated with the Shai-Hulud "Second Coming" NPM supply chain attack. The malware uses a setup_bun.js script to install the Bun runtime if not present, and then executes the malicious bun_environment.js payload.

Known false positives

Legitimate but uncommon use of files named `bun_environment.js` could trigger this rule.

MITRE ATT&CK coverage

Tactic	Techniques
Initial Access	`T1195.002` Supply Chain Compromise: Compromise Software Supply Chain
Execution	`T1203` Exploitation for Client Execution

Telemetry coverage

Provider	Record / event type
Sysmon	Event ID 1: Process creation
Security-Auditing	Event ID 4688: A new process has been created.

Rule body

title: Shai-Hulud Malicious Bun Execution
id: 5299fadf-f228-4526-8274-251db1960be9
related:
    - id: eb827bbd-670a-4d58-8446-c464d8ac2323
      type: similar
status: experimental
description: |
    Detects the execution of `bun_environment.js` via the Bun runtime, a behavior associated with the Shai-Hulud "Second Coming" NPM supply chain attack.
    The malware uses a `setup_bun.js` script to install the Bun runtime if not present, and then executes the malicious `bun_environment.js` payload.
references:
    - https://www.aikido.dev/blog/shai-hulud-strikes-again-hitting-zapier-ensdomains
    - https://www.wiz.io/blog/shai-hulud-2-0-ongoing-supply-chain-attack
    - https://github.com/asyncapi/cli/blob/2efa4dff59bc3d3cecdf897ccf178f99b115d63d/setup_bun.js
    - https://semgrep.dev/blog/2025/digging-for-secrets-sha1-hulud-the-second-coming-of-the-npm-worm/
author: Swachchhanda Shrawan Poudel (Nextron Systems)
date: 2025-11-25
tags:
    - attack.t1195.002
    - attack.t1203
    - attack.execution
    - attack.initial-access
    - detection.emerging-threats
logsource:
    category: process_creation
    product: windows
detection:
    selection_parent:
        ParentImage|endswith: '\node.exe'
    selection_child_bun_script:
        Image|endswith: '\bun.exe'
        CommandLine|contains:
            - 'bun_environment.js'
            - 'https://github.com/actions/runner/releases/download/v2.330.0'
    condition: selection_parent and 1 of selection_child_*
falsepositives:
    - Legitimate but uncommon use of files named `bun_environment.js` could trigger this rule.
level: high
regression_tests_path: regression_data/rules-emerging-threats/2025/Malware/Shai-Hulud/proc_creation_win_mal_shai_hulud_malicious_node_bun_execution/info.yml

Stages and Predicates

Stage 0: `condition`

selection_parent and 1 of selection_child_*

Stage 1: `selection_parent`

selection_parent:
    ParentImage|endswith: '\node.exe'

Stage 2: `selection_child_bun_script`

selection_child_bun_script:
    Image|endswith: '\bun.exe'
    CommandLine|contains:
        - 'bun_environment.js'
        - 'https://github.com/actions/runner/releases/download/v2.330.0'

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`CommandLine`	match	`bun_environment.js` corpus 2 (sigma 2) `https://github.com/actions/runner/releases/download/v2.330.0` corpus 2 (sigma 2)	`field:"CommandLine" kind:match`
`Image`	ends_with	`\bun.exe` corpus 2 (sigma 2)	`field:"Image" kind:ends_with value:"\bun.exe"`
`ParentImage`	ends_with	`\node.exe` corpus 4 (sigma 4)	`field:"ParentImage" kind:ends_with value:"\node.exe"`