Custom compliance checks
Custom image checks give you a way to write and run your own compliance checks to assess, measure, and enforce security baselines in your environment.
Prisma Cloud lets you implement your own custom image checks with simple scripts. Custom compliance checks are supported for Linux containers and hosts and Windows containers.
A custom image check consists of a single script. The script’s exit code determines the result of the check, where 0 is pass and 1 is fail.
Scripts are executed in the default shell. The most common default shell for Linux is bash, but that’s not always the case. For Windows container images, the default shell is cmd.exe.
If you want to use a specific shell, or if your default shell is in a non-standard location, use the shebang interpreter directive at the top of your compliance check to specify the path to the executable. For example, the following directive specifies that the Linux Bourne-again (bash) shell should parse and interpret the compliance check.
For containers, Defender runs the compliance checks inside a restricted sandboxed container instantiated from the image being scanned, thus avoiding the unnecessary risk associated with running arbitrary code.
For hosts, Defender runs the compliance checks on the host itself with unrestricted privileges to allow execution of any script. In order to limit exposure, this feature is disabled by default.
Every compliance check in the system has a unique ID. Custom checks are automatically assigned an ID, starting with the number 9000. As new custom checks are added, they are automatically assigned the next available ID (9001, 9002, and so on).
If a new rule with custom compliance checks is added, or an existing rule is updated with a new custom compliance check, Prisma Cloud drops the cached scan results for registries, and rescans registry images. In a scaled-out environment with large registries, repeated changes to custom compliance checks could have a negative impact on Prisma Cloud’s performance.
Enabling custom compliance checks for hosts
By default, custom compliance checks for hosts is disabled.
If you enable the feature, and then later disable it, the disabled state is effective immediately. You don’t need to redeploy Defenders when you switch to the disabled state. You only need to redeploy Defenders when switching to the enabled state.
- Go toManage > Defenders > Advanced Settings.
- SetCustom Compliance Checks for hoststo enabled.
- Deploy Defenders to your environment. Or if already deployed, redeploy your Defenders.
Creating a new custom check
The flow for writing and operationalizing a custom check is:
- Write a custom check.
- Create a new compliance rule that includes your custom check, and specifies the action to take when the check fails (ignore, alert, block).
- Open Console
- Write a new custom check.
- Go toDefend > Compliance > Custom.
- ClickAdd check.
- Enter a name and description.
- Specify the severity of the compliance issue.
- Enter a script.
- Update the compliance policy to run your check.
- Go toDefend > Compliance > Containers and Imagesfor containers orDefend > Compliance > Hostsfor hosts.
- ClickAdd rule.
- Enter a rule name.
- UnderCompliance actions, narrow the compliance checks displayed.For containers, on theAll typesdrop-down list, selectCustom > Image.For hosts, on theAll typesdrop-down list, selectCustom > Custom.You should see a list of custom checks you’ve implemented, starting with ID 9000.
- Select an action for your custom check (Ignore,Alert, orBlock).
- Validate your setup by reviewing the compliance reports underMonitor > Compliance.
The following example scripts show how to run some basic checks, such as checking file permissions. Use them as starting point for your own scripts. Any special utilities or programs required by your script must be installed in the image being evaluated.
File permissions (Linux)
The following script checks the permissions for the /bin/busybox file. Assuming busybox is installed in your image, this check should pass.
if [ $(stat -c %a /bin/busybox) -eq 755 ]; then echo 'test permission failure' && exit 1; fi
File exists (Linux)
The following script checks if /tmp/foo.txt exists in the container file system. If it doesn’t exist, the check fails.
if [ ! -f /tmp/foo.txt ]; then echo "File not found!" exit 1 fi
User exists (Linux)
The following script checks if the user John exists. If the user exists, the check passes. Otherwise, it fails.
if grep -Fxq "John" /etc/passwd then echo yes else echo "user not found!" exit 1 fi
File exists (Windows)
The following script checks if C:\Users exists. If it does, the check passes.
IF EXIST C:\Users Echo test permission failure && exit 1
File does not exist (Windows)
This check is the inverse of the previous check. The script checks if C:\Users doesn’t exist. If it doesn’t exist, the check passes.
IF NOT EXIST C:\Users Echo test permission failure && exit 1
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