Zip Slip in Flask with Cockroachdb

Zip Slip is a path traversal vulnerability that occurs when an application constructs file paths from user-supplied input without proper validation. In a Flask application using Cockroachdb, the risk emerges not from Cockroachdb itself, but from how file paths are handled before data is written to or read from the database via the application layer. For example, if a Flask route accepts a filename or archive upload and uses user input to determine extraction or storage paths, an attacker can provide paths like ../../../etc/passwd to escape intended directories. When the application writes files to disk—such as temporary extracts for processing user data or backup scripts that later interact with Cockroachdb—the unchecked traversal can overwrite critical system files or expose configuration files that may contain database connection strings.

Consider a Flask endpoint that receives a ZIP file, extracts it, and then imports CSV data into Cockroachdb. If the extraction logic does not sanitize path entries, an archive containing ../../malicious.sql can write outside the target directory. A compromised file at a system level may not directly alter Cockroachdb, but it can inject malicious SQL scripts or configuration changes that the Flask app later uses when connecting to Cockroachdb. This chain illustrates how insecure file handling in Flask combined with Cockroachdb usage can lead to unauthorized data access or execution, even though Cockroachdb does not perform the file operations. The vulnerability is in the Flask component, but the impact can extend to data integrity when database credentials or schema files are exposed.

Moreover, if the Flask application dynamically generates SQL statements using file-derived metadata and passes them to Cockroachdb without validation, an attacker who manipulates file paths may inject crafted data that influences query logic. Although Cockroachdb is resilient against direct path traversal, the surrounding Flask application logic must enforce strict input validation and path normalization to prevent the exploit chain from reaching the database layer. Regular security scans using tools that test unauthenticated attack surfaces can detect these weaknesses by identifying path traversal indicators in API endpoints that handle files and database interactions.

To mitigate Zip Slip in Flask when interacting with Cockroachdb, validate and sanitize all file paths before any filesystem operation. Use Python’s os.path.normpath and ensure the resolved path remains within the intended directory. Below is a secure example of a Flask route that extracts a ZIP file and imports data into Cockroachdb without risking path traversal.

import os
import zipfile
from flask import Flask, request
import psycopg2

app = Flask(__name__)

def get_db_connection():
    return psycopg2.connect(
        host=os.getenv("COCKROACH_HOST"),
        database=os.getenv("COCKROACH_DB"),
        user=os.getenv("COCKROACH_USER"),
        password=os.getenv("COCKROACH_PASSWORD"),
        port=os.getenv("COCKROACH_PORT", 26257)
    )

@app.route('/import', methods=['POST'])
def import_zip():
    if 'file' not in request.files:
        return 'No file uploaded', 400
    file = request.files['file']
    if file.filename == '':
        return 'Empty filename', 400

    # Secure extraction: prevent Zip Slip
    base_dir = os.path.abspath('uploads')
    with zipfile.ZipFile(file.stream, 'r') as zf:
        for member in zf.namelist():
            member_path = os.path.normpath(member)
            abs_path = os.path.abspath(os.path.join(base_dir, member_path))
            if not abs_path.startswith(base_dir):
                return f'Invalid path: {member}', 400
            zf.extract(member, base_dir)

    # After safe extraction, read CSV and insert into Cockroachdb
    import csv
    conn = get_db_connection()
    cursor = conn.cursor()
    csv_path = os.path.join(base_dir, 'data.csv')
    with open(csv_path, 'r') as f:
        reader = csv.reader(f)
        for row in reader:
            cursor.execute(
                'INSERT INTO records (col1, col2) VALUES (%s, %s)',
                (row[0], row[1])
            )
    conn.commit()
    cursor.close()
    conn.close()
    return 'Import successful', 200

Key remediation steps include checking each extracted member’s resolved path against the base directory, avoiding dynamic SQL composition from file content, and using parameterized queries when inserting into Cockroachdb. These practices ensure that even if a malicious archive reaches the Flask layer, it cannot escape the intended directory or inject harmful data into database operations. For ongoing protection, integrate the middleBrick CLI (middlebrick scan <url>) into your development workflow to detect path traversal patterns in unauthenticated scans, or use the GitHub Action to fail builds if security scores drop below your defined threshold.