Language: Python
Label: vulnerable
CWE: CWE-74 \u2014 Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')
The product constructs all or part of a command, data structure, or record using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify how it is parsed or interpreted when it is sent to a downstream component.

Code:
def login():
    user = flask.request.form["username"]
    password = flask.request.form["password"]

    api = flask.current_app.config["PYLOAD_API"]
    user_info = api.check_auth(user, password)

    if not user_info:
        log.error(f"Login failed for user '{user}'")
        return jsonify(False)

    s = set_session(user_info)
    log.info(f"User '{user}' successfully logged in")
    flask.flash("Logged in successfully")

    return jsonify(s)