Block request for multiple unsuccessful logins for

问题:

I have a web site and I want to block request from BOTs and attempt brute force login to my web site.

Now I'm using Session for storing login attempt and show captcha after 3 unsuccessful login but there is a problem.Session will be removed, if user closes the browser.

What kind of solution I should consider to prevent BOTs and brute force login? What property of user system or browser I should store to manage his/her next login?

Edit 1)

I don't use ASP.NET Membership provider. I'm using my own authentication and authorization classes

回答1:

You can't use session, as it requires the client to store a cookie for you, and an attacker is not going to help you out. You will need some global state.

You needn't bother tracking IP addresses, as a bad guy will just use an Anonymyzing Proxy.

Don't use account lock-out unless you have to (PCI requirement), as this just lets the attacker DoS your users.

You also want to avoid DoS-ing yourself by making your server do too much work.

This works:

Upon unsuccessful authentication, store username in global state, along with count. Synchronized count++ if more unsuccessful authentications with that username. I use redis for this.

If count >= threshold, then demand solved CAPTCHA value before proceeding. Show CAPTCHA on login screen.

Upon successful authentication, clear stored username in global state. Give user "trusted user agent" HMAC'd cookie, so they don't have to CAPTCHA in the future for that username on that UA.

You can do the same for passwords, but probably with a higher threshold.

If you don't like CAPTCHA then demand Proof of Work, for example by making the client calculate and submit the prime factors of a very large number.

While you're at it, make sure you are using bcrypt to hash your passwords, and that the cost factor is high enough that it takes >= 250ms to hash a password. This slows down your server but also slows down an attacker. Avoid hashing unless they pass the CAPTCHA (if required).

Encourage users to use long, complicated, memorable? passwords, so that they're harder to brute-force.

回答2:

The easiest would be to front your solution with a CDN provider such as cloudflare (https://www.cloudflare.com/features-security) that will detect bots for you. Lots of the CDNs offer this, and cloudflare have a free tariff.

Alternatively if you are attempting to do this yourself, then you can count the number of attempts per username in your database and present a captcha based on this count.

回答3:

Identify invalid login based on IpAddress(anonymous proxy).That Each invalid login ip and login count&time that will stored in Application State.

Create Class InvalidLogin

public class InvalidLogin
{
    public string IP { get; set; }
    public DateTime Attempttime { get; set; }
    public int AttemptCount { get; set; }
}

Login Event

protected void Login_Click(object sender, EventArgs e)
        {
            bool Testsuccessfullogin = false;
            if (Testsuccessfullogin)
            {
                //Your code after successfull login
            }
            else
            {
               //Invalid Login --- Capture Each login event based on IP
                string strIp;
                strIp = Request.ServerVariables["HTTP_X_FORWARDED_FOR"]; //when user is behind proxy server
                if (strIp == null)
                {
                    strIp = Request.ServerVariables["REMOTE_ADDR"];//Without proxy
                }

                List<InvalidLogin> user = null;
                if (HttpContext.Current.Application["Users"] == null) //Adding List to Application State
                {
                    user = new List<InvalidLogin>();
                }
                else
                {
                    user = (List<InvalidLogin>)HttpContext.Current.Application["Users"];
                }
                var remove = user.RemoveAll(x => x.Attempttime < DateTime.Now.AddMinutes(-15));//Remove IP Before 15 minutes(Give 15 Min Time Next Login)
                var checkLogged = user.Find(x => x.IP == strIp);
                if (checkLogged == null)
                {
                    user.Add(new InvalidLogin
                    {
                        IP = strIp,
                        Attempttime = DateTime.Now,
                        AttemptCount = 1

                    });
                     Application.Lock();
                     HttpContext.Current.Application["Users"] = user;
                      Application.UnLock();
                }
                else
                {
                    if (checkLogged.AttemptCount < 4)
                    {
                        checkLogged.Attempttime = DateTime.Now;
                        checkLogged.AttemptCount++;
                        Application.Lock();
                        HttpContext.Current.Application["Users"] = user;
                        Application.UnLock();
                    }
                }



                if (checkLogged != null)
                {
                    if (checkLogged.AttemptCount > 3)
                    {
                        captcha.Visible = true;  //Showing captcha 
                    }
                }




            }
        }

回答4:

If you are using your own authentication and authorization classes, you need to count the number of failed attempt to login for each user and it's date and time.

If the number of attempts is reached the limit that you will break the next login process with error message like "Your account was blocked for a 15 minutes, please try again later."

For example. Table of logins is named [Logins].

You need to add new colums:
1. [LastLoginAttemptAt] DATETIME NULL
2. [LoginFailedAttemptsCount] INT NOT NULL DEFAULT 0

So, your class Login will have these new fields:

public class Login {
    public DateTime? LastLoginAttemptAt {get;set;}
    public int LoginFailedAttemptsCount {get;set;}
}

Also you need to store somewere configuration variable - the value of max number of failed attempts to login and block period.

const int MaxNumberOfFailedAttemptsToLogin = 10;
const int BlockMinutesAfterLimitFailedAttemptsToLogin = 15; // 15 min

On a signIn method you will do the following (primitive example of code, not a prod-version):

public void SignIn(string username, string password)
{    
    var login = _userService.TryGetLogin(username);
    if (login == null){
        // Login by username not found.
        // Return error message "Invalid username or password"
        return;
    }

    if (login.LoginFailedAttemptsCount > MaxNumberOfFailedAttemptsToLogin
    && login.LastLoginAttemptAt.HasValue
    && DateTime.Now < login.LastLoginAttemptAt.Value.AddMinutes(BlockMinutesAfterLimitFailedAttemptsToLogin))
    {
        // Login is blocked, need to break the process.
        // Return error message "Your account was blocked 
        // for a 15 minutes, please try again later."
        return;
    } else {
        login.LoginFailedAttemptsCount = 0;
        login.LastLoginAttemptAt = DateTime.Now;
    }

    var success = login.ValidatePassword(password);
    if (!success)
    {
        // Invalid password, need to update the number of attempts.
        login.LastLoginAttemptAt = DateTime.Now; //or UTC
        login.LoginFailedAttemptsCount++;
        // Update(login);
        // Return error message "Invalid username or password"
        return;
    } else {
        login.LoginFailedAttemptsCount = 0;
        login.LastLoginAttemptAt = DateTime.Now;
        // Update(login);
        // Success!
    }
}

回答5:

You can suspend the account after few failed attempts and have user answer security questions to re-enable it. Also do not allow the reuse of a last few passwords and you should be safe.

Now that being said if you want to do it via coding then save the third login attempt time [MaxAttemptTime] (DateTime.Now) and time to release the account [ReleaseTime] (say after 20 minutes DateTime.Now.AddMinutes(20)).

Now every time there is an attempt from the same user to login it should be declined based on the [ReleaseTime]. Reset these counters on the successful login for a genuine user.

回答6:

only thing that I'd like to add that others haven't is that where possible, you don't want to alert bots to the fact that they've been detected. if you block them with some message, then they will just make note of what they did to be detected and adjust. if you're "noticing" them by ip for example, just don't allow the password that they're entering to ever succeed. they will be fooled into thinking that you have some complicated passwords etc, and go elsewhere, without ever knowing for sure that you noticed them.

I would also suggest storing the "attempts" in a database with ip. you can then easily go back and review attempts that have been made against your site. you could query the web logs, but that's more painful. I also log successful logins so I can notice when bots do get in to go back and apply further research.

回答7:

If i were doing this i would use a column in a database to store the login attempt number and a date time stamp for the first attempt. Then have some logic around the login

 if(loginAttempt>5 && DateTime.Now<loginDate.AddMinute(5))
{
    //Locked out
}