Ldap Injection in Flask with Cockroachdb

Ldap Injection occurs when untrusted input is concatenated into LDAP query strings without validation or escaping. In a Flask application using Cockroachdb as the primary data store, an LDAP endpoint (for authentication or group lookup) can become an attack surface if user-controlled values are passed directly to an LDAP filter. The database choice (Cockroachdb) does not inherently protect against LDAP Injection; it affects how credentials or session data are stored, while the LDAP interaction remains a separate operation. If Flask builds an LDAP filter like (&(uid=USER_INPUT)) by string interpolation, an attacker can supply )(uid=admin) to change the filter semantics, potentially bypassing authentication or enumerating users.

Consider a Flask route that takes a username and builds an LDAP search filter to validate credentials against an LDAP server:

import ldap
from flask import request

@app.route('/login', methods=['POST'])
def login():
    username = request.form.get('username', '')
    password = request.form.get('password', '')
    # Unsafe: direct string interpolation into LDAP filter
    ldap_filter = f'(&(objectClass=inetOrgPerson)(uid={username}))'
    conn = ldap.initialize('ldap://ldap.example.com')
    try:
        conn.simple_bind_s(ldap_filter, password)
        # If bind succeeds, proceed with Cockroachdb session creation
    except ldap.INVALID_CREDENTIALS:
        return 'Invalid credentials', 401

Here, the LDAP filter is constructed via Python f-string concatenation. An attacker could provide admin)(uid=admin) as the username, resulting in the filter (&(objectClass=inetOrgPerson)(uid=admin)(uid=admin)), which may bypass intended matching rules. Even though Cockroachdb stores user records, the vulnerability exists in the LDAP interaction layer. The scan checks for such unsafe consumption patterns and flags them under the Unsafe Consumption and Input Validation checks.

middleBrick’s LLM/AI Security checks do not apply to this vector, but the scanner’s Input Validation and Unsafe Consumption checks will detect unescaped LDAP filter construction. Findings include severity, references to the OWASP API Top 10 (e.g., A01:2019 – Broken Authentication), and remediation guidance. A compliant approach is to use parameterized filters or strict allowlists, and to avoid direct concatenation of user input into LDAP queries.

Remediation focuses on preventing LDAP Injection by avoiding string interpolation and using parameterized or library-supported filters. Since Cockroachdb is used for application data, ensure that any user identity lookups prior to LDAP binding are validated against a strict allowlist stored in Cockroachdb. Below is a safe pattern using the ldap-filter library to build filters safely:

import ldap
from ldap.filter import escape_filter_chars
from flask import request

@app.route('/login', methods=['POST'])
def login():
    username = request.form.get('username', '')
    password = request.form.get('password', '')
    # Safe: escape special LDAP characters in the input
    safe_username = escape_filter_chars(username)
    ldap_filter = f'(&(objectClass=inetOrgPerson)(uid={safe_username}))'
    conn = ldap.initialize('ldap://ldap.example.com')
    try:
        conn.simple_bind_s(ldap_filter, password)
    except ldap.INVALID_CREDENTIALS:
        return 'Invalid credentials', 401

escape_filter_chars escapes characters such as *, (, ), \\, and \\00, preventing attackers from injecting structural filter components. For additional safety, validate the username against a Cockroachdb-stored allowlist before constructing the LDAP filter:

import psycopg2
from ldap.filter import escape_filter_chars

# Assume a Cockroachdb connection via psycopg2
conn_db = psycopg2.connect(
    host='secure-host.cockroachdb.net',
    port=26257,
    user='app_user',
    password='strong-pass',
    database='app_db'
)

def is_registered_user(username: str) -> bool:
    with conn_db.cursor() as cur:
        # Use parameterized query to avoid SQL Injection
        cur.execute('SELECT 1 FROM users WHERE username = %s', (username,))
        return cur.fetchone() is not None

@app.route('/login', methods=['POST'])
def login():
    username = request.form.get('username', '')
    password = request.form.get('password', '')
    if not is_registered_user(username):
        return 'User not found', 403
    safe_username = escape_filter_chars(username)
    ldap_filter = f'(&(objectClass=inetOrgPerson)(uid={safe_username}))'
    conn = ldap.initialize('ldap://ldap.example.com')
    try:
        conn.simple_bind_s(ldap_filter, password)
    except ldap.INVALID_CREDENTIALS:
        return 'Invalid credentials', 401

This approach combines Cockroachdb-backed identity verification with proper LDAP filter escaping. The scanner’s BFLA/Privilege Escalation and Property Authorization checks can further validate that authorization logic does not rely solely on LDAP group membership without verifying application-level permissions stored in Cockroachdb. middleBrick’s GitHub Action can integrate these checks into CI/CD pipelines to fail builds if insecure patterns are detected, while the CLI allows on-demand scanning from the terminal using middlebrick scan <url>.