
[[password-guess-brute-force-attacks]]
=== Brute force attacks

A brute force attack attempts to guess a user's password by trying to log in multiple times. {project_name} has brute force detection capabilities and can permanently or temporarily disable a user account if the number of login failures exceeds a specified threshold.

[NOTE]
====
When a user is locked and attempts to log in, {project_name} displays the default `Invalid username or password` error message. This message is the same error message as the message displayed for an invalid username or invalid password to ensure the attacker is unaware the account is disabled.
====

[WARNING]
====
Brute force detection is disabled by default. Enable this feature to protect against brute force attacks.
====

To enable this protection:

. Click *Realm Settings* in the menu
. Click the *Security Defenses* tab.
. Click the *Brute Force Detection* tab.
. Choose the *Brute Force Mode* which best fit to your requirements. 
+
.Brute force detection
image:images/brute-force.png[]

==== Lockout permanently
{project_name} disables a user account (blocking log in attempts) until an administrator re-enables it.

.Lockout permanently
image:images/brute-force-permanently.png[]

*Permanent Lockout Parameters*

|===
|Name |Description |Default

|Max Login Failures
|The maximum number of login failures.
|30 failures

|Quick Login Check Milliseconds
|The minimum time between login attempts.
|1000 milliseconds

|Minimum Quick Login Wait
|The minimum time the user is disabled when login attempts are quicker than _Quick Login Check Milliseconds_.
|1 minute

|===

*Permanent Lockout Flow*

====
. On successful login
.. Reset `count`
. On failed login
.. Increment `count`
.. If `count` is greater than or equals to `Max login failures`
... locks the user
.. Else if the time between this failure and the last failure is less than _Quick Login Check Milliseconds_
... Locks the user for the time specified at _Minimum Quick Login Wait_
====

[NOTE]
====
Enabling an user account resets the `count`.
====

==== Lockout temporarily
{project_name} disables a user account for a specific period of time. The time period that the account is disabled increases as the attack continues.

.Lockout temporarily
image:images/brute-force-temporarily.png[]

*Temporary Lockout Parameters*

|===
|Name |Description |Default

|Max Login Failures
|The maximum number of login failures.
|30 failures

|Strategy to increase wait time
|Strategy to increase the time a user will be temporarily disabled when the user's login attempts exceed _Max Login Failures_
|Multiple

|Wait Increment
|The time added to the time a user is temporarily disabled when the user's login attempts exceed _Max Login Failures_.
|1 minute

|Max Wait
|The maximum time a user is temporarily disabled.
|15 minutes

|Failure Reset Time
|The time when the failure count resets. The timer runs from the last failed login. Make sure this number is always greater than `Max wait`; otherwise the effective
wait time will never reach the value you have set to `Max wait`.
|12 hours

|Quick Login Check Milliseconds
|The minimum time between login attempts.
|1000 milliseconds

|Minimum Quick Login Wait
|The minimum time the user is disabled when login attempts are quicker than _Quick Login Check Milliseconds_.
|1 minute

|===

*Temporary Lockout Algorithm*
====
. On successful login
.. Reset `count`
. On failed login
.. If the time between this failure and the last failure is greater than _Failure Reset Time_
... Reset `count`
.. Increment `count`
.. Calculate `wait` according the brute force strategy defined (see below Strategies to set Wait Time).
.. If `wait` is less than or equals to 0 and the time between this failure and the last failure is less than _Quick Login Check Milliseconds_
... set `wait` to _Minimum Quick Login Wait_
.. if `wait` is greater than 0
... Temporarily disable the user for the smallest of `wait` and _Max Wait_ seconds

====

[NOTE]
====
`count` does not increment when a temporarily disabled account commits a login failure.
====

*Strategies to set Wait Time*

{project_name} provides two strategies to calculate wait time: By multiples or Linear. By multiples is the first strategy introduced by {project_name}, so that is the default one. 

By multiples strategy, wait time is incremented when the number (or count) of failures are multiples of `Max Login Failure`. For instance, if you set `Max Login Failures` to `5` and a `Wait Increment` to `30` seconds, the effective time that an account is disabled after several failed authentication attempts will be:

[cols="1,1,1,1"]
|===
|`Number of Failures` | `Wait Increment`  | `Max Login Failures` | `Effective Wait Time`
|1 |30 | 5 | 0
|2 |30 | 5 | 0
|3 |30 | 5 | 0
|4 |30 | 5 | 0
|**5** |**30** | 5 | **30**
|6 |30 | 5 | 30
|7 |30 | 5 | 30
|8 |30 | 5 | 30
|9 |30 | 5 | 30
|**10** |**30** | 5 | **60**
|===

At the fifth failed attempt, the account is disabled for `30` seconds. After reaching the next multiple of `Max Login Failures`, in this case `10`, the time increases from `30` to `60` seconds. 

The By multiple strategy uses the following formula to calculate wait time: _Wait Increment in Seconds_ * (`count` / _Max Login Failures_). The division is an integer division rounded down to a whole number.

For linear strategy, wait time is incremented when the `count` (or number) of failures is greater than or equals to `Max Login Failure`. For instance, if you have set `Max Login Failures` to `5` and a `Wait Increment` to`30` seconds, the effective time that an account is disabled after several failed authentication attempts will be:

[cols="1,1,1,1"]
|===
|`Number of Failures` | `Wait Increment`  | `Max Login Failures` | `Effective Wait Time`
|1 |30 | 5 | 0
|2 |30 | 5 | 0
|3 |30 | 5 | 0
|4 |30 | 5 | 0
|**5** |**30** | 5 | **30**
|**6** |**30** | 5 | **60**
|**7** |**30** | 5 | **90**
|**8** |**30** | 5 | **120**
|**9** |**30** | 5 | **150**
|**10** |**30** | 5 | **180**
|===

At the fifth failed attempt, the account is disabled for `30` seconds. Each new failure increases wait time according value specified at `wait increment`.

The linear strategy uses the following formula to calculate wait time: _Wait Increment in Seconds_ * (1 + `count` - _Max Login Failures_).

==== Lockout permanently after temporary lockout
Mixed mode. Locks user temporarily for specified number of times and then locks user permanently. 

.Lockout permanently after temporary lockout
image:images/brute-force-mixed.png[]

*Permanent lockout after temporary lockouts Parameters*

|===
|Name |Description |Default

|Max Login Failures
|The maximum number of login failures.
|30 failures

|Maximum temporary Lockouts
|The maximum number of temporary lockouts permitted before permanent lockout occurs.
|1

|Strategy to increase wait time
|Strategy to increase the time a user will be temporarily disabled when the user's login attempts exceed _Max Login Failures_
|Multiple

|Wait Increment
|The time added to the time a user is temporarily disabled when the user's login attempts exceed _Max Login Failures_.
|1 minute

|Max Wait
|The maximum time a user is temporarily disabled.
|15 minutes

|Failure Reset Time
|The time when the failure count resets. The timer runs from the last failed login. Make sure this number is always greater than `Max wait`; otherwise the effective
wait time will never reach the value you have set to `Max wait`.
|12 hours

|Quick Login Check Milliseconds
|The minimum time between login attempts.
|1000 milliseconds

|Minimum Quick Login Wait
|The minimum time the user is disabled when login attempts are quicker than _Quick Login Check Milliseconds_.
|1 minute

|===

*Permanent lockout after temporary lockouts Algorithm*
====
. On successful login
.. Reset `count`
.. Reset `temporary lockout` counter
. On failed login
.. If the time between this failure and the last failure is greater than _Failure Reset Time_
... Reset `count`
... Reset `temporary lockout` counter
.. Increment `count`
.. Calculate `wait` according the brute force strategy defined (see below Strategies to set Wait Time).
.. If `wait` is less than or equals to 0 and the time between this failure and the last failure is less than _Quick Login Check Milliseconds_
... set `wait` to _Minimum Quick Login Wait_
... set `quick login failure` to `true``
.. if `wait` and `Maximum temporary Lockouts` is greater than 0
... set `wait` to the smallest of `wait` and _Max Wait_ seconds
.. if `quick login failure` is `false`
... Increment `temporary lockout` counter
.. If `temporary lockout` counter exceeds `Maximum temporary lockouts`
... Permanently locks the user
.. Else
... Temporarily blocks the user according `wait` value

====

[NOTE]
====
`count` does not increment when a temporarily disabled account commits a login failure.
====

==== Downside of {project_name} brute force detection

The downside of {project_name} brute force detection is that the server becomes vulnerable to denial of service attacks. When implementing a denial of service attack, an attacker can attempt to log in by guessing passwords for any accounts it knows and eventually causing {project_name} to disable the accounts.

Consider using intrusion prevention software (IPS). {project_name} logs every login failure and client IP address failure. You can point the IPS to the {project_name} server's log file, and the IPS can modify firewalls to block connections from these IP addresses.
