exfil

web-security/module.yml

@@ -42,6 +42,8 @@ challenges:
   name: XSS 5
 - id: xss-rf-post
   name: XSS 6
+- id: xss-exfil-cookie
+  name: XSS 7
 - id: level-11
   name: CSRF 1
   description: Exploit a cross site request forgery vulnerability

web-security/xss-exfil-cookie/DESCRIPTION.md

@@ -0,0 +1,14 @@
+Depending on the attacker's goals, what they might actually be after is the victim's entire account.
+For example, attackers might use XSS to exfiltrate victim authentication data and then use this data to take over the victim's account.
+
+Authentication data is often stored via browser cookies, such as what happened in `Authentication Bypass 2` (but, typically, much more secure).
+If an attacker can leak these cookies, the result can be disastrous for the victim.
+
+This level stores the authentication data for the logged in user in a cookie.
+You must use XSS to leak this cookie so that you can, in turn, use it in a request to impersonate the `admin` user.
+This exfiltration will happen over HTTP to a server that you run, and everything you need is available via JavaScript's `fetch()` and its ability to access (some) site cookies.
+
+----
+**HINT:**
+By "server that you run", we really mean that listening on a port with `nc` will be sufficient.
+Look at the `-l` and `-v` options to `nc`.

web-security/xss-exfil-cookie/server

@@ -0,0 +1,117 @@
+#!/opt/pwn.college/python
+
+import tempfile
+import sqlite3
+import flask
+import os
+
+app = flask.Flask(__name__)
+
+class TemporaryDB:
+    def __init__(self):
+        self.db_file = tempfile.NamedTemporaryFile("x", suffix=".db")
+
+    def execute(self, sql, parameters=()):
+        connection = sqlite3.connect(self.db_file.name)
+        connection.row_factory = sqlite3.Row
+        cursor = connection.cursor()
+        result = cursor.execute(sql, parameters)
+        connection.commit()
+        return result
+
+flag = open("/flag").read().strip() if os.geteuid() == 0 else "pwn.college{fake_flag}"
+
+db = TemporaryDB()
+# https://www.sqlite.org/lang_createtable.html
+db.execute("""CREATE TABLE IF NOT EXISTS posts AS SELECT ? AS content, "admin" AS author, FALSE AS published""", [flag])
+db.execute("""CREATE TABLE IF NOT EXISTS users AS SELECT "admin" AS username, ? as password""", [flag[-10:]])
+# https://www.sqlite.org/lang_insert.html
+db.execute("""INSERT INTO users SELECT "guest" as username, "password" as password""")
+db.execute("""INSERT INTO users SELECT "hacker" as username, "1337" as password""")
+
+@app.route("/login", methods=["POST"])
+def challenge_login():
+    username = flask.request.form.get("username")
+    password = flask.request.form.get("password")
+    if not username:
+        flask.abort(400, "Missing `username` form parameter")
+    if not password:
+        flask.abort(400, "Missing `password` form parameter")
+
+    # https://www.sqlite.org/lang_select.html
+    user = db.execute("SELECT * FROM users WHERE username = ? AND password = ?", (username, password)).fetchone()
+    if not user:
+        flask.abort(403, "Invalid username or password")
+
+    response = flask.redirect("/")
+    response.set_cookie('auth', username+"|"+password)
+    return response
+
+@app.route("/draft", methods=["POST"])
+def challenge_draft():
+    username, password = flask.request.cookies.get("auth", "|").split("|")
+    user = db.execute("SELECT * FROM users WHERE username = ? AND password = ?", (username, password)).fetchone()
+    if not user:
+        flask.abort(403, "Invalid username or password")
+
+    if username == "admin":
+        flask.abort(400, "pwnpost no longer supports admin posting due to rampant flag disclosure")
+
+    content = flask.request.form.get("content", "")
+    # https://www.sqlite.org/lang_insert.html
+    db.execute(
+        "INSERT INTO posts (content, author, published) VALUES (?, ?, ?)",
+        (content, username, bool(flask.request.form.get("publish")))
+    )
+    return flask.redirect("/")
+
+@app.route("/publish", methods=["POST"])
+def challenge_publish():
+    username, password = flask.request.cookies.get("auth", "|").split("|")
+    user = db.execute("SELECT * FROM users WHERE username = ? AND password = ?", (username, password)).fetchone()
+    if not user:
+        flask.abort(403, "Invalid username or password")
+
+    if username == "admin":
+        flask.abort(400, "pwnpost no longer supports admin posting due to rampant flag disclosure")
+
+    # https://www.sqlite.org/lang_update.html
+    db.execute("UPDATE posts SET published = TRUE WHERE author = ?", [username])
+    return flask.redirect("/")
+
+@app.route("/", methods=["GET"])
+def challenge_get():
+    page = "<html><body>\nWelcome to pwnpost, now with users!<hr>\n"
+    username, password = flask.request.cookies.get("auth", "|").split("|")
+    user = db.execute("SELECT * FROM users WHERE username = ? AND password = ?", (username, password)).fetchone()
+    if user:
+        page += """
+            <form action=draft method=post>
+              Post:<textarea name=content>Write something!</textarea>
+              <input type=checkbox name=publish>Publish
+              <input type=submit value=Save>
+            </form><br>
+            <form action=publish method=post><input type=submit value="Publish All Drafts"></form><hr>
+        """
+
+        for post in db.execute("SELECT * FROM posts").fetchall():
+            page += f"""<h2>Author: {post["author"]}</h2>"""
+            if post["published"]:
+                page += post["content"] + "<hr>\n"
+            elif post["author"] == username:
+                page += "<b>YOUR DRAFT POST:</b> " + post["content"] + "<hr>\n"
+            else:
+                page += f"""(Draft post, showing first 12 characters):<br>{post["content"][:12]}<hr>"""
+    else:
+        page += """
+            <form action=login method=post>
+              Username:<input type=text name=username>
+              Password:<input type=text name=password>
+              <input type=submit name=submit value=Login>
+            </form><hr>
+        """
+
+    return page + "</body></html>"
+
+app.secret_key = os.urandom(8)
+app.run("challenge.localhost", 8080 if os.geteuid() else 80)

web-security/xss-exfil-cookie/victim

@@ -0,0 +1,77 @@
+#!/opt/pwn.college/python
+
+import contextlib
+import urllib
+import time
+import sys
+import os
+
+from selenium import webdriver
+from selenium.webdriver.firefox.options import Options as FirefoxOptions
+from selenium.webdriver.firefox.service import Service as FirefoxService
+from selenium.webdriver.common.by import By   
+from selenium.webdriver.support.wait import WebDriverWait
+from selenium.webdriver.support import expected_conditions as EC
+from selenium.common.exceptions import TimeoutException, WebDriverException
+
+os.setuid(os.geteuid())
+os.environ.clear()
+os.environ["PATH"] = "/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
+
+@contextlib.contextmanager
+def run_browser():
+    options = FirefoxOptions()
+    options.add_argument("--headless")
+
+    # workaround for ubuntu
+    if os.path.exists("/snap/bin/geckodriver"):
+        service = FirefoxService(executable_path="/snap/bin/geckodriver", log_path="/dev/null")
+    else:
+        service = FirefoxService(log_path="/dev/null")
+    driver = webdriver.Firefox(service=service, options=options)
+
+    try:
+        yield driver
+    finally:
+        driver.quit()
+
+if len(sys.argv) <= 1:
+    print(f"Usage: {sys.argv[0]} URL")
+    sys.exit(1)
+
+url = sys.argv[1]
+url_parsed = urllib.parse.urlparse(url)
+try:
+    assert url_parsed.hostname == "challenge.localhost", "hostname should be 'challenge.localhost'"
+    assert url_parsed.port in {None, 80, 8080}, "port should be 80 or 8080"
+except AssertionError as e:
+    print(f"Invalid URL: {e}")
+    sys.exit(2)
+
+
+print("Visiting the URL!")
+with run_browser() as browser:
+    try:
+        browser.get(url)
+        print("URL loaded...")
+
+        print("Logging in as admin...")
+        login = {
+            "username": "admin",
+            "password": (open("/flag").read().strip() if url_parsed.port != 8080 else "pwn.college{fake_flag}")[-10:]
+        }
+        for name, value in login.items():
+            field = browser.find_element(By.NAME, name)
+            field.send_keys(value)
+        submit_field = browser.find_element(By.NAME, "submit")
+        submit_field.submit()
+
+        WebDriverWait(browser, 10).until(EC.staleness_of(submit_field))
+        time.sleep(3)
+        print("Visited! Go check if the attack worked!")
+    except WebDriverException as e:
+        if "can%E2%80%99t%20establish%20a%20connection" in str(e):
+            print("Connection error! Is the service running?")
+        else:
+            print(f"Failure: {e}...")
+        sys.exit(4)