GitHub Artifact Download from Cross-Fork Workflow

Severity: medium
Time window: 90m
Match by: workflow_job.run_id, workflow_run.id
Tags: CI/CD, Workflow, Supply Chain, Artifact Poisoning
Reference: https://www.legitsecurity.com/blog/artifact-poisoning-vulnerability-discovered-in-rust
Source: github.com/panther-labs/panther-analysis

The "download artifacts" API, and various custom actions encapsulating it, doesn't differentiate between artifacts that were uploaded by forked repositories and base repositories, which could lead privileged workflows to download artifacts that were created by forked repositories and that are potentially poisoned.

MITRE ATT&CK coverage

Tactic	Techniques
Initial Access	`T1195.002` Supply Chain Compromise: Compromise Software Supply Chain
Execution	`T1072` Software Deployment Tools
Privilege Escalation	`T1134` Access Token Manipulation

Rule body yaml

AnalysisType: correlation_rule
RuleID: "GitHub.ArtifactDownload.FROM.CrossFork.Workflow"
DisplayName: "GitHub Artifact Download from Cross-Fork Workflow"
Enabled: true
Severity: Medium
Tags:
  - CI/CD
  - Workflow
  - Supply Chain
  - Artifact Poisoning
Reports:
  MITRE ATT&CK:
    - TA0001:T1195.002  # Supply Chain Compromise: Compromise Software Supply Chain
    - TA0002:T1072  # Execution: Software Deployment Tools
    - TA0004:T1134  # Privilege Escalation: Access Token Manipulation
Description: >
  The "download artifacts" API, and various custom actions encapsulating it,
  doesn't differentiate between artifacts that were uploaded by forked repositories 
  and base repositories, which could lead privileged workflows to download artifacts
  that were created by forked repositories and that are potentially poisoned.
Runbook: |
  1. Consider ensuring that the artifact download job uses the specific run_id for the generated artifact. 
     It is recommended to specify which run id or commit hash to download the artifact from.
  2. Consider filtering out artifacts created from pull requests.
  3. Consider limiting the possibility for outside collaborators to trigger workflows.
  4. Sanitize cross-fork contents.
Reference: https://www.legitsecurity.com/blog/artifact-poisoning-vulnerability-discovered-in-rust
Detection:
  - Group:
      - ID: CrossForkWorkflowRun
        RuleID: GitHub.CrossFork.Workflow.Run
      - ID: ArtifactDownload
        RuleID: GitHub.Webhook.WorkflowArtifactDownload
    MatchCriteria:
      field_name:
        - GroupID: CrossForkWorkflowRun
          Match: workflow_run.id
        - GroupID: ArtifactDownload
          Match: workflow_job.run_id
    EventEvaluationOrder: Chronological
    LookbackWindowMinutes: 90
    Schedule:
      RateMinutes: 60
      TimeoutMinutes: 10
Tests:
  - Name: cross-fork workflow with artifact download
    ExpectedResult: true
    RuleOutputs:
      - ID: CrossForkWorkflowRun
        Matches:
          workflow_run.id:
            "12345678":
              - "2025-10-15T18:41:00Z"
      - ID: ArtifactDownload
        Matches:
          workflow_job.run_id:
            "12345678":
              - "2025-10-15T18:42:00Z"

  - Name: cross-fork workflow without artifact download
    ExpectedResult: false
    RuleOutputs:
      - ID: CrossForkWorkflowRun
        Matches:
          workflow_run.id:
            "12345678":
              - "2025-10-15T18:41:00Z"

Detection logic

Stage 1: `step CrossForkWorkflowRun`

References detection GitHub.CrossFork.Workflow.Run.

Stage 2: `step ArtifactDownload`

References detection GitHub.Webhook.WorkflowArtifactDownload.

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`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
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`groupby:`	Entity-grouping substring match against `group_by_keys`: `groupby:user`, `groupby:host`
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`-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)

GitHub Artifact Download from Cross-Fork Workflow

MITRE ATT&CK coverage

Rule body yaml

Detection logic

Stage 1: `step CrossForkWorkflowRun`

Stage 2: `step ArtifactDownload`

Keyboard shortcuts

Search operators

GitHub Artifact Download from Cross-Fork Workflow

MITRE ATT&CK coverage

Rule body yaml

Detection logic

Stage 1: step CrossForkWorkflowRun

Stage 2: step ArtifactDownload

Stage 1: `step CrossForkWorkflowRun`

Stage 2: `step ArtifactDownload`