Shai-Hulud Malicious Bun Execution - Linux

Status: experimental
Severity: high
Log source: product linux, category process_creation
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.

MITRE ATT&CK coverage

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

Event coverage

Provider	Event
Sysmon-for-Linux	Event ID 1

Rule body yaml

title: Shai-Hulud Malicious Bun Execution - Linux
id: eb827bbd-670a-4d58-8446-c464d8ac2323
related:
    - id: 5299fadf-f228-4526-8274-251db1960be9
      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
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: linux
detection:
    selection_parent:
        ParentImage|endswith: '/node'
    selection_child_bun:
        Image|endswith: '/bun'
        CommandLine|contains:
            - 'bun_environment.js'
            - 'https://github.com/actions/runner/releases/download/v2.330.0'
    selection_child_setup_curl:
        CommandLine|contains|all:
            - 'curl '
            - '-fsSL'
            - 'https://bun.sh/install'
            - 'bash'
    selection_child_path_reload:
        CommandLine|contains|all:
            - 'bash -c "source '
            - '&& echo'
    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

Stages and Predicates

Stage 0: `condition`

selection_parent and 1 of selection_child_*

Stage 1: `selection_parent`

selection_parent:
    ParentImage|endswith: '/node'

Stage 2: `selection_child_bun`

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

Stage 3: `selection_child_setup_curl`

selection_child_setup_curl:
    CommandLine|contains|all:
        - 'curl '
        - '-fsSL'
        - 'https://bun.sh/install'
        - 'bash'

Stage 4: `selection_child_path_reload`

selection_child_path_reload:
    CommandLine|contains|all:
        - 'bash -c "source '
        - '&& echo'

Indicators

Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.

Field	Kind	Values
`CommandLine`	match	`&& echo` `-fsSL` `bash` `bash -c "source` `bun_environment.js` `curl` `https://bun.sh/install` `https://github.com/actions/runner/releases/download/v2.330.0`
`Image`	ends_with	`/bun`
`ParentImage`	ends_with	`/node`

`j` / `k`	Scroll down / up
`d` / `u`	Half-page down / up
`gg` / `G`	Top / bottom
`h` / `l`	History back / forward
`f`	Follow link (`Shift` = new tab)
`/`	Focus search
`?`	Toggle this help
`↑` / `↓`	Navigate search results
`Enter`	Open highlighted result
`Esc`	Close results / dialog

`type:`	`events` / `rules` / `providers`
`vendor:`	`sigma` / `elastic` / `splunk` / `kusto` / `chronicle` (vendor name alone also works: `sigma:`, `kql:`, `secops:`…)
`tactic:`	TA-id, slug, or name: `credential_access`, `TA0006`
`technique:`	technique or sub-technique ID: `T1003`, `T1003.001` (alias `tech:`)
`severity:`	`critical` / `high` / `medium` / `low` / `informational` (alias `sev:`)
`risk_score`	Numeric comparison on the Elastic risk score (0 to 100): `risk_score>50`, `risk_score<=20`, `risk_score=99` (alias `risk`; Elastic rules only)
`stages:`	Rules with exactly N pipeline stages
`correlation:`	`single_event` / `sequence` / `alternatives` / `alternatives_cross_log` / `all_required` / `correlated`
`with:`	Co-occurrence event-id; stacks (`with:4624 with:4769`) to require all, while a comma list in one occurrence (`with:4624,4769`) is an either-or group. Implies multi-event
`like:`	Structural neighbors of a rule slug (equivalents + subsumption stricter / broader): `like:comsvcs_lsass_memory_dump-splunk-sysmon`
`groupby:`	Entity-grouping substring match against `group_by_keys`: `groupby:user`, `groupby:host`
`uses:`	Rules whose predicate tree touches the field (any kind, any value): `uses:CommandLine`
`excludes:`	Rules with top-level `not()` clauses on the field (FP whitelists): `excludes:ParentImage`
`field:` / `value:`	Predicate search; narrows rule cards to those with a matching leaf and drives the indicator tier. Unquoted = substring, wildcards allowed (`value:mimikatz`)
`indicator:`	Shorthand for `field:F value:V`: `indicator:Image=*\powershell.exe`
`kind:`	Filter by predicate kind. Narrows rule cards to those carrying a matching predicate leaf (`vendor:elastic kind:cidr_match`) and drives the indicator tier: `contains` / `starts_with` / `ends_with` / `regex` / `cidr` / `eq` / `in` … (operator aliases `op:`/`match:`)
`has:` / `no:`	`sample`, `field`, `notes`, `refs`, `trace`, `thirdparty`, `rule`, `pattern`, `timewindow`, `threshold`, `newterms`, `sigma`/`elastic`/`splunk`/`kusto`/`chronicle`
`-op:val`	Exclude matches; works on most operators but not `type:`/`like:`/`has:`/`no:` (use `no:<flag>` to exclude a rule flag): `tactic:execution -vendor:splunk`. Standalone `-kind:`/`-field:`/`-value:` drop every rule carrying a matching predicate leaf (`type:rules -kind:is_null`)
`field:"…"` / `value:"…"`	Quoted value = anchored exact match (also allows spaces): `value:"net user"`
`a,b`	Comma = OR inside one operator (`vendor:sigma,elastic`, `severity:high,critical`); repeating a facet merges the same way. `field:`/`value:` never split (literal commas)
`vendors:` / `stage:`	Singular and plural spellings fold to the canonical operator and value: `tactics:` = `tactic:`, `type:event` = `type:events`, `correlation:sequences` = `correlation:sequence`, `has:thresholds` = `has:threshold`
`"quoted phrase"`	Exact-match a multi-word phrase (free text)

Shai-Hulud Malicious Bun Execution - Linux

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `selection_parent`

Stage 2: `selection_child_bun`

Stage 3: `selection_child_setup_curl`

Stage 4: `selection_child_path_reload`

Indicators

Keyboard shortcuts

Search operators

Shai-Hulud Malicious Bun Execution - Linux

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: selection_parent

Stage 2: selection_child_bun

Stage 3: selection_child_setup_curl

Stage 4: selection_child_path_reload

Indicators

Stage 0: `condition`

Stage 1: `selection_parent`

Stage 2: `selection_child_bun`

Stage 3: `selection_child_setup_curl`

Stage 4: `selection_child_path_reload`