GHSA-cxww-7g56-2vh6 #

Summary #

Field	Value
CVE	CVE-2024-42471
Affected Action	actions/download-artifact
Severity	High
CVSS Score	8.6/10 (CVSS:4.0)
Vulnerability Type	Path Traversal / Zip-Slip (CWE-22)
Published	2024-08-12

Vulnerability Description #

The official actions/download-artifact action versions 4.0.0 to 4.1.2 contain an Arbitrary File Write via Artifact Extraction vulnerability (Zip Slip). When downloading and extracting a specially crafted artifact containing path traversal filenames, the action is vulnerable to arbitrary file write.

This is a “Zip Slip” vulnerability where malicious actors can exploit path traversal sequences in archived files to write files outside the intended extraction directory during artifact extraction. Malicious artifacts can contain files with paths like ../../../../etc/passwd or ../../../.github/workflows/malicious.yml, allowing attackers to write files outside the intended extraction directory.

Impact: Attackers with low-level privileges can remotely exploit this vulnerability over a network without user interaction, resulting in high confidentiality and integrity impacts on the vulnerable system.

This vulnerability enables attackers to:

Overwrite critical files (workflows, scripts, configuration)
Inject malicious code into the repository
Escalate privileges by modifying workflow files
Compromise the CI/CD pipeline

Credits: Justin Taft from Google

Affected versions: >= 4.0.0, < 4.1.3 Patched versions: 4.1.3 and higher (users can also use the ‘v4’ tag which points to the latest secure version)

Vulnerable Pattern #

name: Vulnerable Pattern
on:
  pull_request:

jobs:
  process:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4

      # Vulnerable: v4.1.2 and earlier have zip-slip vulnerability
      # Malicious artifact can write to ../../../../.github/workflows/
      - uses: actions/download-artifact@v4.1.2
        with:
          name: build-output
          path: ./artifacts

      - name: Process artifacts
        run: |
          ls -R ./artifacts
          # If artifact contains ../../../.github/workflows/backdoor.yml
          # it overwrites workflow files with malicious code

Why this is vulnerable:

No validation of file paths during extraction
Attacker can craft artifact with ../ path traversal
Can overwrite arbitrary files in workspace
Particularly dangerous for overwriting workflow files

Attack Scenario:

Attacker creates malicious artifact with file: ../../../.github/workflows/backdoor.yml
Uploads artifact in pull request build
Victim workflow downloads artifact with v4.1.2
Extraction writes backdoor.yml to workflow directory
Next workflow run executes attacker’s code with secrets

Safe Pattern #

name: Safe Pattern
on:
  pull_request:

jobs:
  process:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4

      # Safe: v4.1.8+ includes path validation and zip-slip protection
      - uses: actions/download-artifact@fa0a91b85d4f404e444e00e005971372dc801d16 # v4.1.8
        with:
          name: build-output
          path: ./artifacts

      - name: Process artifacts
        run: |
          ls -R ./artifacts
          # Path traversal attempts are blocked
          # Files are extracted only within ./artifacts

Why this is safe:

v4.1.8+ validates and normalizes all file paths
Paths with .. components are rejected
Files are confined to extraction directory
Protection against zip-slip and path traversal attacks

sisakulint Detection Result #

script/actions/advisory/GHSA-cxww-7g56-2vh6-vulnerable.yaml:20:9: artifact is downloaded to an unsafe path "./artifacts" at step "<unnamed>". Workspace-relative paths allow malicious artifacts to overwrite source code, scripts, or dependencies, creating a critical supply chain vulnerability. Extract to '${{ runner.temp }}/artifacts' instead. See https://sisaku-security.github.io/lint/docs/rules/artifactpoisoningcritical/ [artifact-poisoning-critical]
script/actions/advisory/GHSA-cxww-7g56-2vh6-vulnerable.yaml:20:9: Action 'actions/download-artifact@v4.1.2' has a known high severity vulnerability (GHSA-cxww-7g56-2vh6): @actions/download-artifact has an Arbitrary File Write via artifact extraction. Upgrade to version 4.1.3 or later. See: https://github.com/advisories/GHSA-cxww-7g56-2vh6 [known-vulnerable-actions]

Analysis #

Detected	Rule	Category Match
Yes	KnownVulnerableActionsRule	Yes
Yes	ArtifactPoisoningCriticalRule	Yes

Detection Details:

KnownVulnerableActionsRule successfully detects actions/download-artifact@v4.1.2 with CVE-2024-42471
ArtifactPoisoningCriticalRule detects unsafe extraction path ./artifacts (workspace-relative)
Provides specific remediation: Upgrade to version 4.1.3 or later
Auto-fix available: Updates to patched version and safe extraction path

Mitigation Recommendations #

Update immediately: Upgrade to v4.1.8 or later (pin to commit SHA)
Pin to safe SHA: Use actions/download-artifact@fa0a91b85d4f404e444e00e005971372dc801d16
Audit past runs: Check if malicious artifacts were used in previous runs
Review workspace: Verify no unauthorized files were written
Limit artifact trust: Download artifacts only from trusted sources
Add validation: Verify artifact contents before processing
Use protected branches: Prevent workflow file modifications without review

Technical Details #

Vulnerable Code Pattern:

# Vulnerable extraction (conceptual)
with zipfile.ZipFile(artifact_path) as zf:
    for member in zf.namelist():
        # No path validation - dangerous!
        zf.extract(member, destination)

Safe Code Pattern:

# Safe extraction with validation
with zipfile.ZipFile(artifact_path) as zf:
    for member in zf.namelist():
        # Validate and normalize path
        target = os.path.normpath(os.path.join(destination, member))
        if not target.startswith(destination):
            raise SecurityError("Path traversal detected")
        zf.extract(member, destination)