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Table of Contents

Administration Guide

Configuring anomaly detection policy

How an anomaly detection model is built?

FortiWeb uses machine learning model to analyze the parameters in your domain and decide whether the value of the parameter is legitimate or not. The machine learning model is built upon vast amount of parameter value samples collected from the real requests to the domain.

When a sample is collected, the system generalized it into a pattern. For example, “abcd_123@abc.com” and “abcdefgecdf_12345678@efg.com” will both be generalized to the pattern “A_N@A.A”. The anomaly detection model is built based on the patterns, not the raw samples.

FortiWeb analyzes the characteristics of the patterns and builds an initial model when 400 samples are collected. The system runs the initial model to detect anomalies, while it keeps collecting more samples to refine it.

Once the number of samples accumulates to 1200, the system will evaluate whether the patterns vary largely since the initial model is built:

  • If there are very few patterns generalized, it indicates the patterns are stable. The system will switch the initial model to a standard model.
  • If a lot of new patterns keeps coming in, the system will continue collecting more samples to cover as much patterns as possible. It won't switch to standard model until the patterns become stable.

The standard model is much more reliable and accurate compared with the initial model. However, your domains may change as new URLs are added and existing parameters provide new functions. This means the mathematical model of the same parameter might be different from what FortiWeb originally observed. To keep the machine learning model up to date, FortiWeb continues collecting new samples to update it, where the outdated patterns are discarded and new patterns are introduced.

Creating an Anomaly Detection policy

Anomaly detection policies are part of a server policy. They are created on the Policy > Sever Policy page. All anomaly detection policies that you create will show up on the Machine Learning > Anomaly Detection page, where you can configure or edit them to your preference.

To configure an anomaly detection policy:

  1. Click Machine Learning > Anomaly Detection .
  2. Double-click the server policy that contains the desired anomaly detection policy (or highlight it and then click the Edit button on top of the page) to open it. The Edit Anomaly Detection Configuration page opens, which breaks down anomaly detection policy into several sections, each of which has various parameters you can use to configure the policy.
  3. Follow the instructions in the following subsections to configure an anomaly detection policy.
  4. Click OK when done.

Some of the machine learning configurations are available only in CLI, for example, the sample number of the initial and the standard models, how frequently the model is updated, etc. Please refer to config waf machine-learning-policy in FortiWeb CLI Reference.

Such settings are hidden in Web UI and default values for them are used. This is sufficient for most cases. We don't recommend to change the settings through CLI unless you know well the impact of the them on the machine learning model.

Sections & Parameters Function
Anomaly Detection Settings
Strictness Level for Anomaly

The value of the strictness level ranges from 1 to 10.

The system uses the following formula to calculate whether a sample is an anomaly:

The probability of the anomaly > μ + the strictness level * σ

If the probability of the sample is larger than the value of "μ + the strictness level * σ", this sample will be identified as anomaly.

μ and σ are calculated based on the probabilities of all the samples collected during the sample collection period, where μ is the average value of all the parameters' probabilities, σ is the standard deviation. They are fixed values. So, the value of "μ + the strictness level * σ" varies with the strictness level you set. The smaller the value of the strictness level is, the more strict the anomaly detection model will be.

This options set a global value for all the parameters. If you want to adjust the strictness level for a specific parameter, See Manage anomaly-detecting settings.

Threat Models

The system scans anomalies to verify whether they are attacks. It provides a method to check whether an anomaly is a real attack by the trained Support Vector Machine Model.

Click Edit to enable or disable threat models for different types of threats such as cross-site scripting, SQL injection and code injection. Currently, seven trained Support Vector Machine Model are provided for seven attack types.

Domain Settings

Create New

  • Add domains to let FortiWeb perform sample collection and intrusion detection on those domains. You can use wildcard * to represent multiple domains. Refer to Maximum number of ADOMs, policies, & server pools per appliance for the maximum domain number supported by the Machine Learning feature for your FortiWeb Model.
  • (View Domain)

  • View anomaly detection reports for that specific domain. The URLs and parameters in this domains are listed. See Viewing domain data
  • (Refresh)

    Refresh the models of the corresponding domain.

    Note:Refreshing deletes all existing learning results.

    (Export)

    Export the anomaly detection data of this domain.

    Delete

    Remove the selected domain(s).

    Note: This will remove all machine-learning results related to the domain(s) as well.

    Import

    Import the anomaly detection data from your local directory to FortiWeb

    Action Settings
    Action

    All requests are scanned first by HMM and then by Threat model.

    Double click the cells in the Action Settings table to choose the action FortiWeb takes when attack is verified for each of the following situations:

    • Alert—Accepts the connection and generates an alert email and/or log message.
    • Alert & Deny—Blocks the request (or resets the connection) and generates an alert and/or log message.
    • Period Block—Blocks the request for a certain period of time.
    Block Period

    Enter the number of seconds that you want to block the requests. The valid range is 1–3,600 seconds (1 hour).

    This option only takes effect when you choose Period Block in Action.

    Severity

    Select the severity level for this anomaly type. The severity level will be displayed in the alert email and/or log message.

    Trigger Action

    Select a trigger policy that you have set in Log&Report > Log Policy > Trigger Policy. If potential or definite anomaly or HTTP Method Violation is detected, it will trigger the system to send email and/or log messages according to the trigger policy.

    IP List Type and Source IP list

    Add IP ranges in the Source IP list, then select Trust or Black to allow or disallow collecting traffic data samples from these IP addresses.

    • Trust: The system will collect samples only from the IP ranges in the Source IP list.
    • Black: The system will collect sample from any IP addresses except the ones in the Source IP list.

    Whether selecting Trust or Black, if you leave the Source IP list blank, the system will collect traffic data samples from any IP addresses. The maximum number of samples collected from each random IP address is 30. You can change the maximum value through CLI command waf machine-learning-policy.

    If you select Trust, then add IP ranges in the Source IP list, the sample collection limit will not take effect, which means FortiWeb will collect traffic data samples only from the specified IP ranges and will not limit the number of samples.

    URL Replacer Policy

    Select the name of the URL Replacer Policy that you have created in Machine Learning Templates.

    If web applications have dynamic URLs or unusual parameter styles, you must adapt URL Replacer Policy to recognize them.

    If you have not created an URL Replacer Policy yet, you can leave this option empty for now, and then edit this policy later when the URL Replacer Policy is created. For more information on URL Replacer Policy, see Configure a URL replacer rule

    Configuring anomaly detection policy

    How an anomaly detection model is built?

    FortiWeb uses machine learning model to analyze the parameters in your domain and decide whether the value of the parameter is legitimate or not. The machine learning model is built upon vast amount of parameter value samples collected from the real requests to the domain.

    When a sample is collected, the system generalized it into a pattern. For example, “abcd_123@abc.com” and “abcdefgecdf_12345678@efg.com” will both be generalized to the pattern “A_N@A.A”. The anomaly detection model is built based on the patterns, not the raw samples.

    FortiWeb analyzes the characteristics of the patterns and builds an initial model when 400 samples are collected. The system runs the initial model to detect anomalies, while it keeps collecting more samples to refine it.

    Once the number of samples accumulates to 1200, the system will evaluate whether the patterns vary largely since the initial model is built:

    • If there are very few patterns generalized, it indicates the patterns are stable. The system will switch the initial model to a standard model.
    • If a lot of new patterns keeps coming in, the system will continue collecting more samples to cover as much patterns as possible. It won't switch to standard model until the patterns become stable.

    The standard model is much more reliable and accurate compared with the initial model. However, your domains may change as new URLs are added and existing parameters provide new functions. This means the mathematical model of the same parameter might be different from what FortiWeb originally observed. To keep the machine learning model up to date, FortiWeb continues collecting new samples to update it, where the outdated patterns are discarded and new patterns are introduced.

    Creating an Anomaly Detection policy

    Anomaly detection policies are part of a server policy. They are created on the Policy > Sever Policy page. All anomaly detection policies that you create will show up on the Machine Learning > Anomaly Detection page, where you can configure or edit them to your preference.

    To configure an anomaly detection policy:

    1. Click Machine Learning > Anomaly Detection .
    2. Double-click the server policy that contains the desired anomaly detection policy (or highlight it and then click the Edit button on top of the page) to open it. The Edit Anomaly Detection Configuration page opens, which breaks down anomaly detection policy into several sections, each of which has various parameters you can use to configure the policy.
    3. Follow the instructions in the following subsections to configure an anomaly detection policy.
    4. Click OK when done.

    Some of the machine learning configurations are available only in CLI, for example, the sample number of the initial and the standard models, how frequently the model is updated, etc. Please refer to config waf machine-learning-policy in FortiWeb CLI Reference.

    Such settings are hidden in Web UI and default values for them are used. This is sufficient for most cases. We don't recommend to change the settings through CLI unless you know well the impact of the them on the machine learning model.

    Sections & Parameters Function
    Anomaly Detection Settings
    Strictness Level for Anomaly

    The value of the strictness level ranges from 1 to 10.

    The system uses the following formula to calculate whether a sample is an anomaly:

    The probability of the anomaly > μ + the strictness level * σ

    If the probability of the sample is larger than the value of "μ + the strictness level * σ", this sample will be identified as anomaly.

    μ and σ are calculated based on the probabilities of all the samples collected during the sample collection period, where μ is the average value of all the parameters' probabilities, σ is the standard deviation. They are fixed values. So, the value of "μ + the strictness level * σ" varies with the strictness level you set. The smaller the value of the strictness level is, the more strict the anomaly detection model will be.

    This options set a global value for all the parameters. If you want to adjust the strictness level for a specific parameter, See Manage anomaly-detecting settings.

    Threat Models

    The system scans anomalies to verify whether they are attacks. It provides a method to check whether an anomaly is a real attack by the trained Support Vector Machine Model.

    Click Edit to enable or disable threat models for different types of threats such as cross-site scripting, SQL injection and code injection. Currently, seven trained Support Vector Machine Model are provided for seven attack types.

    Domain Settings

    Create New

  • Add domains to let FortiWeb perform sample collection and intrusion detection on those domains. You can use wildcard * to represent multiple domains. Refer to Maximum number of ADOMs, policies, & server pools per appliance for the maximum domain number supported by the Machine Learning feature for your FortiWeb Model.
  • (View Domain)

  • View anomaly detection reports for that specific domain. The URLs and parameters in this domains are listed. See Viewing domain data
  • (Refresh)

    Refresh the models of the corresponding domain.

    Note:Refreshing deletes all existing learning results.

    (Export)

    Export the anomaly detection data of this domain.

    Delete

    Remove the selected domain(s).

    Note: This will remove all machine-learning results related to the domain(s) as well.

    Import

    Import the anomaly detection data from your local directory to FortiWeb

    Action Settings
    Action

    All requests are scanned first by HMM and then by Threat model.

    Double click the cells in the Action Settings table to choose the action FortiWeb takes when attack is verified for each of the following situations:

    • Alert—Accepts the connection and generates an alert email and/or log message.
    • Alert & Deny—Blocks the request (or resets the connection) and generates an alert and/or log message.
    • Period Block—Blocks the request for a certain period of time.
    Block Period

    Enter the number of seconds that you want to block the requests. The valid range is 1–3,600 seconds (1 hour).

    This option only takes effect when you choose Period Block in Action.

    Severity

    Select the severity level for this anomaly type. The severity level will be displayed in the alert email and/or log message.

    Trigger Action

    Select a trigger policy that you have set in Log&Report > Log Policy > Trigger Policy. If potential or definite anomaly or HTTP Method Violation is detected, it will trigger the system to send email and/or log messages according to the trigger policy.

    IP List Type and Source IP list

    Add IP ranges in the Source IP list, then select Trust or Black to allow or disallow collecting traffic data samples from these IP addresses.

    • Trust: The system will collect samples only from the IP ranges in the Source IP list.
    • Black: The system will collect sample from any IP addresses except the ones in the Source IP list.

    Whether selecting Trust or Black, if you leave the Source IP list blank, the system will collect traffic data samples from any IP addresses. The maximum number of samples collected from each random IP address is 30. You can change the maximum value through CLI command waf machine-learning-policy.

    If you select Trust, then add IP ranges in the Source IP list, the sample collection limit will not take effect, which means FortiWeb will collect traffic data samples only from the specified IP ranges and will not limit the number of samples.

    URL Replacer Policy

    Select the name of the URL Replacer Policy that you have created in Machine Learning Templates.

    If web applications have dynamic URLs or unusual parameter styles, you must adapt URL Replacer Policy to recognize them.

    If you have not created an URL Replacer Policy yet, you can leave this option empty for now, and then edit this policy later when the URL Replacer Policy is created. For more information on URL Replacer Policy, see Configure a URL replacer rule