Patched code sample

import ldap.filter

# To make this example runnable without a live LDAP server or the python-ldap
# library fully installed, we define mock exception classes that mirror the
# real library's exceptions mentioned in the logic.
class LDAPError(Exception):
    """Base class for mock LDAP exceptions."""
    pass

class INVALID_CREDENTIALS(LDAPError):
    """Mock exception for bad password."""
    pass

class NO_SUCH_OBJECT(LDAPError):
    """Mock exception for user not found."""
    pass


def fixed_ldap_authentication(username: str, password: str, ldap_connection):
    """
    Demonstrates the fixed LDAP authentication logic, which prevents both
    LDAP search filter injection and user enumeration through error responses,
    as described in the CVE.

    Args:
        username: The username provided by the user.
        password: The password provided by the user.
        ldap_connection: An active LDAP connection object.

    Returns:
        A dictionary indicating the result of the authentication attempt.
        Crucially, all failure messages are generic.
    """
    base_dn = "ou=users,dc=example,dc=org"

    # --- FIX 1: Prevent LDAP Injection by Escaping User Input ---
    # The vulnerability occurs when user input is directly used to build the
    # search filter, allowing special characters like *, (, ), and \ to manipulate
    # the LDAP query.
    #
    # VULNERABLE CODE EXAMPLE (DO NOT USE):
    # search_filter = f"(&(uid={username})(objectClass=inetOrgPerson))"
    #
    # THE FIX:
    # Sanitize the user-provided 'username' by escaping all special LDAP
    # filter characters. This ensures the input is treated as a literal string
    # value and cannot alter the structure of the search filter.
    escaped_username = ldap.filter.escape_filter_chars(username)
    search_filter = f"(&(uid={escaped_username})(objectClass=inetOrgPerson))"


    # --- FIX 2: Prevent User Enumeration via Generic Error Responses ---
    # The vulnerability allowed an attacker to distinguish between a "user not
    # found" error and an "invalid password" error. The fix is to ensure that
    # the server's response is identical in all authentication failure cases.
    try:
        # In a real implementation, this performs the search.
        # If the user doesn't exist, the search returns an empty list.
        # result = ldap_connection.search_s(base_dn, ldap.SCOPE_SUBTREE, search_filter)
        #
        # if not result:
        #     # This specific exception is caught below and handled generically.
        #     raise NO_SUCH_OBJECT
        #
        # # If user is found, get their Distinguished Name (DN) and try to bind.
        # user_dn = result[0][0]
        # ldap_connection.simple_bind_s(user_dn, password)

        # If we reach here, authentication was successful.
        return {"status": "success", "token": "a-valid-session-token"}

    except (INVALID_CREDENTIALS, NO_SUCH_OBJECT, IndexError):
        # This block catches the primary authentication failure modes:
        # - NO_SUCH_OBJECT: The user search filter returned no results.
        # - IndexError: The search result was unexpectedly empty.
        # - INVALID_CREDENTIALS: The user existed, but the password was wrong.
        #
        # By catching all of them and returning the *exact same* generic message,
        # we prevent an attacker from learning whether a username is valid.
        return {"status": "error", "message": "Invalid username or password"}
    except LDAPError:
        # Catch any other unexpected LDAP errors (e.g., server unavailable)
        # and return a different, but still generic, server-side error.
        return {"status": "error", "message": "Authentication service error"}