Manage Threat Detection Rules

Review Understanding Threat Detection Rules to get started.

Access the Rules Library

  1. Select Policies > Rules | Rules Library.

  2. The Rules Library is displayed.


  • Grouped: Rules are grouped by source and you can collapse or open the groupings as needed.

  • Search: Click the magnifying glass if the Search field is not automatically opened. Search by words in the rule name.

  • Published by: Remember that default (Falco) rules show up as Published by: Sysdig ; user-created rules show as Published by: Secure UI. See also: Edit a Rule.

  • Last Updated: Sort by the date the rule was added/updated. Note that badges highlight rules that were added or changed in the past 7 days.

  • Usage: Shows number of policies where the rule and used, and whether the policies are enabled. Click the rule to see the policy names in the Rule Detail panel.

  • Tags associated with the rule (colored boxes).

Available Filters

Use the various filters to find rules:

  • Usage Type: Choose rules that have been Enabled, Disabled, or Not Used in a policy
  • Rule Source: In addition to being grouped by source, you can also filter down to show only particular sources
  • Managed Type: Choose Managed Rule (from Sysdig) or Custom Rule

Create a Rule

There are different interfaces for creating Falco rules vs. list-matching rules.

Create a Falco Rule

  1. From the Rules Library page, click +Add Rule and select Falco from the drop-down.

    The New Rule page for the Falco rule type is displayed.

  2. Enter the parameters:

    Name and Description: create a name and a meaningful description for the rule

    Condition and Output: write the condition code and outputs required. See Supported Fields for more information.

    Priority: This is a required field to meet the Falco rule syntax.

    Source: Define if the rule is detecting events using the Kubernetes Audit data source or using the standard syscall mechanisms

    Tags: Select relevant tags from the drop-down or add your own custom tag

  3. Click Save.

Falco rules with the source k8s_audit need Kubernetes Audit logging enabled for conditions to be met.

Create a List-Matching Rule: Container Type Example

Suppose you want detect whenever someone used a specific container image that has known problems. In this case, a Container rule would be appropriate. (The other list-matching rule types have similar entry fields, as appropriate to their type.)

  1. From the Rules Library page, click +Add Rule and select Container from the drop-down.

    The New Rule page for the Container rule type is displayed.

  2. Enter the parameters:

    Name: Enter a Name, e.g. Problematic Images.

    Description: Enter a Description, e.g. Images that shouldn’t be used

    If Matching/ If Not Matching: Select If Matching. When added to a policy, if the rule conditions match, then the policy action you define (such as “send notification”) will be triggered.

    Containers: Add the container name(s) that are problematic, e.g. cassandra:3.0.23.

    Tags: Select relevant tags from the dropdown, e.g. database and container.

  3. Click Save.

Review a Rule Detail Panel

From the Rules Library list, select a rule to see its details.

From here you can:

  • Review the rule definition, including clicking embedded macros to open their details in a pop-up window
  • Check all policies in which the rule is used and see whether those policies are enabled or disabled.

Edit a Rule

Any rules published by Sysdig are default and are read-only. You can append to their lists and macros, but cannot change the core parameters. Default rules cannot be deleted.

Self-created rules can be freely edited. You can also override the behavior of default Falco rules and macros using a placeholder mechanism in the Rules Editor.

To display existing rules:

  1. Select Policies > Rules | Rules Library and select a rule.

  2. The Rule Details panel opens on the right. You can review the parameters and append to macros and lists inline if desired.

Append to Falco Macros and Lists

Default Falco rules have a variety of macros and lists embedded in them. While these cannot be deleted from a default rule, you can append additional information onto them.

For example, consider the Policy DB Program Spawned Process in the screenshot above. The embedded rule is used to check that databases have not spawned illicit processes. You can see in the rule condition the Falco list : db_server_binaries.

To append items in a default list:

  1. Click the blue list text in the rule condition, or go to Policies > Falco Lists and search for it by name.

  2. The list content is displayed. Click Append.

  3. Enter the additional items (i.e. databases) you want to include in the rule and click Save.

    The same process applies to macros.

How to Use the Rules Editor

The Rules Editor allows you can freely create custom Falco rules, lists, and macros and can override the behavior of the defaults.

Understand the Interface

To access the interface, select Policies > Rules Editor:

The Right Panel (Default)

Displays the rules_yamls provided from Sysdig.

  • Contains the default rules and macros

  • Is read-only

The Left Panel (Custom)

Displays the custom rules and overrides you want to add to the selected rules_yaml.

Note that many default Falco rules and macros have a parallel placeholder entry (commented out) in the yaml file. These have the prefix user_known. To change the behavior of a default rule, it is recommended to copy the placeholder equivalent into the custom rules panel and edit it there, rather than editing the default rule directly.

To search the rules YAML files

Click inside the Rules Editor right panel and use CNRL F to open an internal search field .

See also: Runtime Policy Tuning .

Use Cases: List-Matching Rules

It is more helpful to think of the rules as matching the activity, rather than using concepts of allowing or denying. (The Network types can be a little confusing in this regard; see the last two use cases for more detail on that type). Thus, the use cases are based on answering the question: What do I want to know?


when any process other than web server programs are run:

  • Rule Type: Process

  • If Not Matching

  • Entries: [apache, httpd, nginx]

if any of the following crypto-mining processes are run:

  • Rule Type: Process

  • If Matching

  • Entries: [minerd, ccminer]

if any program reads any file containing password-related information:

  • Rule Type: Filesystem

  • Read Operations: If Matching

  • Entries: /etc/shadow, /etc/sudoers, /etc/pam.conf, /etc/security/pwquality.conf

if any program writes anywhere below binary directories:

  • Rule Type: Filesystem

  • Read/Write Operations: If Matching

  • Entries: /usr, /usr/bin, /bin

if a program writes to anywhere other than /var/tmp:

  • Rule Type: Filesystem

  • Read/Write Operations: If Not Matching

  • Entries: /var/tmp

if any container with an image from is started:

  • Rule Type: Container

  • If Matching

  • Entries: []

if any container runs an Apache web server:

  • Rule Type: Container

  • If Matching

  • Entries: [httpd, amd64/httpd]

I want to know if any container with a non-database image is started:

  • Rule Type: Container

  • If Not Matching

  • Entries [percona/percona-server, mysql, postgres]

if any program accepts an inbound ssh connection:

  • Rule Type: Network

  • Tcp, "If Matching"

  • Entries: [22]

if any program receives a DNS datagram:

  • Rule Type: Network

  • UDP, "If Matching"

  • Entries: [53]

if any program accepts a connection on a port other than http/https

  • Rule Type: Network

  • TCP, "If Not Matching"

  • Entries: [80, 443]

if any program accepts any inbound connection:

  • Rule Type: Network

  • Inbound Connection: Deny

if any program makes any outbound connection

  • Rule Type: Network

  • Outbound Connection: Deny