简介

该漏洞是一个CTFd的账户接管漏洞，在注册和修改密码处，存在逻辑漏洞，从而导致可以修改任意账号密码。

影响版本：v2.0.0-2.2.2

漏洞分析

首先定位到用户注册处：/CTFd/auto.py

@auth.route("/register", methods=["POST", "GET"])
@check_registration_visibility
@ratelimit(method="POST", limit=10, interval=5)
def register():
errors = get_errors()
if request.method == "POST":
name = request.form["name"]
email_address = request.form["email"]
password = request.form["password"]
​
name_len = len(name) == 0
names = Users.query.add_columns("name", "id").filter_by(name=name).first()
emails = (
Users.query.add_columns("email", "id")
.filter_by(email=email_address)
.first()
)
pass_short = len(password.strip()) == 0
pass_long = len(password) > 128
valid_email = validators.validate_email(request.form["email"])
team_name_email_check = validators.validate_email(name)
​
if not valid_email:
errors.append("Please enter a valid email address")
if email.check_email_is_whitelisted(email_address) is False:
errors.append(
"Only email addresses under {domains} may register".format(
domains=get_config("domain_whitelist")
)
)
if names:
errors.append("That user name is already taken")
if team_name_email_check is True:
errors.append("Your user name cannot be an email address")
if emails:
errors.append("That email has already been used")
if pass_short:
errors.append("Pick a longer password")
if pass_long:
errors.append("Pick a shorter password")
if name_len:
errors.append("Pick a longer user name")
​
if len(errors) > 0:
return render_template(
"register.html",
errors=errors,
name=request.form["name"],
email=request.form["email"],
password=request.form["password"],
)
else:
with app.app_context():
user = Users(
name=name.strip(),
email=email_address.lower(),
password=password.strip(),
)
db.session.add(user)
db.session.commit()
db.session.flush()
​
login_user(user)
​
if config.can_send_mail() and get_config(
"verify_emails"
):  # Confirming users is enabled and we can send email.
log(
"registrations",
format="[{date}] {ip} - {name} registered (UNCONFIRMED) with {email}",
)
email.verify_email_address(user.email)
db.session.close()
return redirect(url_for("auth.confirm"))
else:  # Don't care about confirming users
if (
config.can_send_mail()
):  # We want to notify the user that they have registered.
email.sendmail(
request.form["email"],
"You've successfully registered for {}".format(
get_config("ctf_name")
),
)
​
log("registrations", "[{date}] {ip} - {name} registered with {email}")
db.session.close()
​
if is_teams_mode():
return redirect(url_for("teams.private"))
​
return redirect(url_for("challenges.listing"))
else:
return render_template("register.html", errors=errors)

上述代码，有一大半是进行输入检测的，提取出来关键部分：

def register():
errors = get_errors()
if request.method == "POST":
name = request.form["name"]
email_address = request.form["email"]
password = request.form["password"]
​
name_len = len(name) == 0
names = Users.query.add_columns("name", "id").filter_by(name=name).first()
emails = (
Users.query.add_columns("email", "id")
.filter_by(email=email_address)
.first()
)
pass_short = len(password.strip()) == 0
pass_long = len(password) > 128
valid_email = validators.validate_email(request.form["email"])
team_name_email_check = validators.validate_email(name)

if len(errors) > 0:         #检测出错

'''注册账户密码插入数据库'''
else:                   
with app.app_context():
user = Users(
name=name.strip(),
email=email_address.lower(),
password=password.strip(),
)
db.session.add(user)
db.session.commit()
db.session.flush()
​
login_user(user)
​
if config.can_send_mail() and get_config(
"verify_emails"
):  # Confirming users is enabled and we can send email.
log(
"registrations",
format="[{date}] {ip} - {name} registered (UNCONFIRMED) with {email}",
)
email.verify_email_address(user.email)
db.session.close()
return redirect(url_for("auth.confirm"))

上方的上半部分，接受用户的输入信息：

def register():
errors = get_errors()
if request.method == "POST":
name = request.form["name"]
email_address = request.form["email"]
password = request.form["password"]
​
name_len = len(name) == 0
names = Users.query.add_columns("name", "id").filter_by(name=name).first()
emails = (
Users.query.add_columns("email", "id")
.filter_by(email=email_address)
.first()
)
pass_short = len(password.strip()) == 0
pass_long = len(password) > 128
valid_email = validators.validate_email(request.form["email"])
team_name_email_check = validators.validate_email(name)

其关键在于这里：

names = Users.query.add_columns("name", "id").filter_by(name=name).first()

在判断用户是否已经注册时，是直接用的name，也就是用户输入的账户名，并且没有任何的过滤。

在下半部分，注册成功时，将账户、密码、邮箱插入到数据库中：

with app.app_context():
user = Users(
name=name.strip(),
email=email_address.lower(),
password=password.strip(),
)
db.session.add(user)
db.session.commit()
db.session.flush()

但是这里又对用户输入的账户进行了去除空格的操作。（也就是说，如果数据库中存在m1sn0w这个账户，但是，如果我在注册时输入的账户名为：空格m1sn0w，那么，注册时不会提示账户已存在，而是将m1sn0w这个用户名插入到数据库中，也就是数据库中有了同名用户）

接下来是第二个利用点（修改密码）：提取出主要代码

@auth.route("/reset_password", methods=["POST", "GET"])
@auth.route("/reset_password/<data>", methods=["POST", "GET"])
@ratelimit(method="POST", limit=10, interval=60)
def reset_password(data=None):
if data is not None:
try:
name = unserialize(data, max_age=1800)
except (BadTimeSignature, SignatureExpired):
return render_template(
"reset_password.html", errors=["Your link has expired"]
)
except (BadSignature, TypeError, base64.binascii.Error):
return render_template(
"reset_password.html", errors=["Your reset token is invalid"]
)
​
if request.method == "GET":
return render_template("reset_password.html", mode="set")
if request.method == "POST":
user = Users.query.filter_by(name=name).first_or_404()
user.password = request.form["password"].strip()
db.session.commit()
log(
"logins",
format="[{date}] {ip} -  successful password reset for {name}",
name=name,
)
db.session.close()
return redirect(url_for("auth.login"))

我们知道，在修改密码时，会向相应的邮箱发送一封邮件，点击之后，才能修改密码。（上面的data值，也就是发送给指定邮箱的URL后面的一串值）

接下来，看看data值是什么：/CTFd/utils/email/__init__.py

def forgot_password(email, team_name):
token = serialize(team_name)
text = """Did you initiate a password reset? Click the following link to reset your password:
​
{0}/{1}
​
""".format(
url_for("auth.reset_password", _external=True), token
)
​
return sendmail(email, text)

可以看到，它是将用户名序列化之后，拼接到相应URL后面，发送给邮箱。（通过前面的分析，我们知道数据库中的账号有两个是同名，那么进行修改密码操作时，就会修改第一个用户的密码）

（有些文章说需要修改当前用户为其他的用户名，但感觉好像不需要）

if request.method == "POST":
user = Users.query.filter_by(name=name).first_or_404()
user.password = request.form["password"].strip()
db.session.commit()

它这里取出来的用户就是第一个用户（也就是先前注册的那个用户）

所以，大致的利用方法如下：

1、注册一个账号，和想要修改的那个用户名同名，但在注册时加上空格

2、点击修改密码，在邮箱确认，即可修改指定用户密码