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LDAP query built from user-controlled sources

ID: py/ldap-injection
Kind: path-problem
Security severity: 9.8
Severity: error
Precision: high
Tags:
   - security
   - external/cwe/cwe-090
Query suites:
   - python-code-scanning.qls
   - python-security-extended.qls
   - python-security-and-quality.qls

Click to see the query in the CodeQL repository

If an LDAP query or DN is built using string concatenation or string formatting, and the components of the concatenation include user input without any proper sanitization, a user is likely to be able to run malicious LDAP queries.

Recommendation

If user input must be included in an LDAP query or DN, it should be escaped to avoid a malicious user providing special characters that change the meaning of the query. In Python2, user input should be escaped with ldap.dn.escape_dn_chars or ldap.filter.escape_filter_chars, while in Python3, user input should be escaped with ldap3.utils.dn.escape_rdn or ldap3.utils.conv.escape_filter_chars depending on the component tainted by the user. A good practice is to escape filter characters that could change the meaning of the query (https://tools.ietf.org/search/rfc4515#section-3).

Example

In the following examples, the code accepts both username and dc from the user, which it then uses to build a LDAP query and DN.

The first and the second example uses the unsanitized user input directly in the search filter and DN for the LDAP query. A malicious user could provide special characters to change the meaning of these components, and search for a completely different set of values.

from flask import request, Flask
import ldap


@app.route("/normal")
def normal():
    unsafe_dc = request.args['dc']
    unsafe_filter = request.args['username']

    dn = "dc={}".format(unsafe_dc)
    search_filter = "(user={})".format(unsafe_filter)

    ldap_connection = ldap.initialize("ldap://127.0.0.1")
    user = ldap_connection.search_s(
        dn, ldap.SCOPE_SUBTREE, search_filter)

from flask import request, Flask
import ldap3


@app.route("/normal")
def normal():
    unsafe_dc = request.args['dc']
    unsafe_filter = request.args['username']

    dn = "dc={}".format(unsafe_dc)
    search_filter = "(user={})".format(unsafe_filter)

    srv = ldap3.Server('ldap://127.0.0.1')
    conn = ldap3.Connection(srv, user=dn, auto_bind=True)
    conn.search(dn, search_filter)

In the third and fourth example, the input provided by the user is sanitized before it is included in the search filter or DN. This ensures the meaning of the query cannot be changed by a malicious user.

from flask import request, Flask
import ldap
import ldap.filter
import ldap.dn


@app.route("/normal")
def normal():
    unsafe_dc = request.args['dc']
    unsafe_filter = request.args['username']

    safe_dc = ldap.dn.escape_dn_chars(unsafe_dc)
    safe_filter = ldap.filter.escape_filter_chars(unsafe_filter)

    dn = "dc={}".format(safe_dc)
    search_filter = "(user={})".format(safe_filter)

    ldap_connection = ldap.initialize("ldap://127.0.0.1")
    user = ldap_connection.search_s(
        dn, ldap.SCOPE_SUBTREE, search_filter)

from flask import request, Flask
import ldap3
from ldap3.utils.dn import escape_rdn
from ldap3.utils.conv import escape_filter_chars


@app.route("/normal")
def normal():
    unsafe_dc = request.args['dc']
    unsafe_filter = request.args['username']

    safe_dc = escape_rdn(unsafe_dc)
    safe_filter = escape_filter_chars(unsafe_filter)

    dn = "dc={}".format(safe_dc)
    search_filter = "(user={})".format(safe_filter)

    srv = ldap3.Server('ldap://127.0.0.1')
    conn = ldap3.Connection(srv, user=dn, auto_bind=True)
    conn.search(dn, search_filter)

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