Zip Slip on Digitalocean

Detecting Zip Slip in Digitalocean environments requires examining both application code and runtime behavior. Start with static analysis of your Digitalocean-hosted applications:

#!/usr/bin/env python3
import os
import zipfile
import fnmatch

def find_zip_extraction_vulnerabilities(root_dir):
    vulnerabilities = []
    for dirpath, _, filenames in os.walk(root_dir):
        for filename in filenames:
            if fnmatch.fnmatch(filename, '*.py'):
                filepath = os.path.join(dirpath, filename)
                with open(filepath, 'r') as f:
                    content = f.read()
                    
                    if 'extractall' in content and '..' in content:
                        vulnerabilities.append({
                            'file': filepath,
                            'issue': 'extractall with path traversal'
                        })
                    
                    if 'ZipArchive' in content and 'extractTo' in content:
                        vulnerabilities.append({
                            'file': filepath,
                            'issue': 'PHP ZipArchive without validation'
                        })
    
    return vulnerabilities

issues = find_zip_extraction_vulnerabilities('/var/www/app')
for issue in issues:
    print(f"VULNERABILITY: {issue['file']} - {issue['issue']}")

For Digitalocean App Platform users, middleBrick provides automated scanning that detects Zip Slip vulnerabilities without requiring code access. The scanner tests archive extraction endpoints by submitting crafted ZIP files containing path traversal payloads.

Runtime detection on Digitalocean Droplets involves monitoring file system activity. Using auditd or similar tools:

auditctl -w /etc -p wa -k critical_files
auditctl -w /var/www -p wa -k web_root

# Monitor for suspicious archive extraction
auditctl -a exit,always -F arch=b64 -S open -F a0=/usr/bin/unzip -k unzip_activity

Digitalocean Spaces users should enable Object Storage Access Logs and analyze for unusual file creation patterns. A Zip Slip attack might create files in unexpected locations or with unusual timestamps.

middleBrick's black-box scanning specifically tests for Zip Slip by:

• Submitting ZIP archives with ../../ traversal sequences
• Checking if extracted files appear outside intended directories
• Verifying that archive contents match expected file structures
• Testing with archives containing absolute paths like /etc/passwd

The scanner runs 12 parallel security checks, including path traversal testing, and provides severity ratings with remediation guidance specific to your Digitalocean deployment architecture.

Remediating Zip Slip in Digitalocean environments requires both code fixes and infrastructure considerations. For Node.js applications on Digitalocean App Platform:

const path = require('path');
const fs = require('fs');

function safeExtract(zipBuffer, extractDir) {
    const safeExtractDir = path.resolve(extractDir);
    
    return new Promise((resolve, reject) => {
        const zipStream = unzipper.PassThrough();
        
        zipStream
            .on('entry', (entry) => {
                const sanitized = path.normalize(entry.path)
                    .replace(/^(/)/, '');
                
                if (sanitized.startsWith('..')) {
                    entry.autodrain();
                    return;
                }
                
                const targetPath = path.join(safeExtractDir, sanitized);
                if (!targetPath.startsWith(safeExtractDir)) {
                    entry.autodrain();
                    return;
                }
                
                entry.pipe(fs.createWriteStream(targetPath));
            })
            .on('error', reject)
            .on('finish', resolve);
        zipStream.write(zipBuffer);
        zipStream.end();
    });
}

For Python applications on Digitalocean Droplets, use the safer zipfile.ZipFile.extractall() with validation:

import zipfile
import os
from pathlib import Path

def safe_extract_all(zip_file, target_dir):
    target_dir = Path(target_dir).resolve()
    
    with zipfile.ZipFile(zip_file, 'r') as archive:
        for member in archive.namelist():
            # Validate path - reject absolute paths and parent directory references
            if member.startswith('/') or '..' in member:
                raise ValueError(f'Invalid path in archive: {member}')
                
            # Calculate target path and validate it stays within target_dir
            target_path = target_dir / member
            if not str(target_path).startswith(str(target_dir)):
                raise ValueError(f'Path traversal detected: {member}')
                
        # All paths validated, perform extraction
        archive.extractall(target_dir)

Digitalocean Kubernetes users should implement admission controllers to prevent malicious archives in Helm charts:

apiVersion: admissionregistration.k8s.io/v1
kind: ValidatingWebhookConfiguration
metadata:
  name: zip-slip-validator
webhooks:
  - name: zip-slip.validation.io
    rules:
      - operations: ['CREATE']
        apiGroups: ['']
        apiVersions: ['v1']
        resources: ['pods']
    webhook:
      url: https://validator.example.com/zip-slip
      timeoutSeconds: 5
      failurePolicy: Fail

For Digitalocean Spaces, implement server-side validation before processing archives:

import re

def validate_archive_contents(file_like_object):
    # Read first 100KB to check for suspicious patterns
    sample = file_like_object.read(102400)
    file_like_object.seek(0)
    
    # Check for path traversal patterns
    if b'../' in sample or b'..' + os.sep.encode() in sample:
        return False, 'Path traversal detected'
        
    # Check for absolute paths
    if b'/' in sample[:100]:
        return False, 'Absolute paths detected'
        
    return True, 'Valid'

Digitalocean App Platform users should configure deployment pipelines to scan for Zip Slip vulnerabilities using middleBrick's GitHub Action before deployment:

name: Security Scan
on: [push, pull_request]

jobs:
  security-scan:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
      - name: Run middleBrick Scan
        uses: middlebrick/middlebrick-action@v1
        with:
          target_url: ${{ secrets.APP_URL }}
          fail_below_score: C
        env:
          MIDDLEBRICK_API_KEY: ${{ secrets.MIDDLEBRICK_API_KEY }}

Implement runtime monitoring on Digitalocean Droplets to detect Zip Slip exploitation attempts:

#!/bin/bash
inotifywait -m /var/www/uploads -e create -e modify | while read path action file; do
    if [[ $file == *.zip ]]; then
        echo "ZIP file detected: $file"
        # Trigger validation before extraction
        python3 validate_zip.py "$path/$file"
    fi
done