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Configure and validate exclusions for Microsoft Defender for Endpoint on Linux

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Applies to:

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This article provides information on how to define exclusions that apply to on-demand scans, and real-time protection and monitoring.

Important

The exclusions described in this article don't apply to other Defender for Endpoint on Linux capabilities, including endpoint detection and response (EDR). Files that you exclude using the methods described in this article can still trigger EDR alerts and other detections.

You can exclude certain files, folders, processes, and process-opened files from Defender for Endpoint on Linux scans.

Exclusions can be useful to avoid incorrect detections on files or software that are unique or customized to your organization. They can also be useful for mitigating performance issues caused by Defender for Endpoint on Linux.

Warning

Defining exclusions lowers the protection offered by Defender for Endpoint on Linux. You should always evaluate the risks that are associated with implementing exclusions, and you should only exclude files that you are confident are not malicious.

Supported exclusion types

The follow table shows the exclusion types supported by Defender for Endpoint on Linux.

Exclusion Definition Examples
File extension All files with the extension, anywhere on the device .test
File A specific file identified by the full path /var/log/test.log
/var/log/*.log
/var/log/install.?.log
Folder All files under the specified folder (recursively) /var/log/
/var/*/
Process A specific process (specified either by the full path or file name) and all files opened by it /bin/cat
cat
c?t

Important

The paths above must be hard links, not symbolic links, in order to be successfully excluded. You can check if a path is a symbolic link by running file <path-name>.

File, folder, and process exclusions support the following wildcards:

Wildcard Description Examples
* Matches any number of any characters including none (note if this wildcard is not used at the end of the path then it will substitute only one folder) /var/*/tmp includes any file in /var/abc/tmp and its subdirectories, and /var/def/tmp and its subdirectories. It does not include /var/abc/log or /var/def/log

/var/*/ includes any file in /var and its subdirectories.
? Matches any single character file?.log includes file1.log and file2.log, but notfile123.log

Note

When using the * wildcard at the end of the path, it will match all files and subdirectories under the parent of the wildcard.

How to configure the list of exclusions

From the management console

For more information on how to configure exclusions from Puppet, Ansible, or another management console, see Set preferences for Defender for Endpoint on Linux.

From the command line

Run the following command to see the available switches for managing exclusions:

mdatp exclusion

Tip

When configuring exclusions with wildcards, enclose the parameter in double-quotes to prevent globbing.

Examples:

  • Add an exclusion for a file extension:

    mdatp exclusion extension add --name .txt

    Extension exclusion configured successfully

  • Add an exclusion for a file:

    mdatp exclusion file add --path /var/log/dummy.log

    File exclusion configured successfully

  • Add an exclusion for a folder:

    mdatp exclusion folder add --path /var/log/

    Folder exclusion configured successfully

  • Add an exclusion for a second folder:

    mdatp exclusion folder add --path /var/log/
mdatp exclusion folder add --path /other/folder

    Folder exclusion configured successfully

  • Add an exclusion for a folder with a wildcard in it:

    mdatp exclusion folder add --path "/var/*/tmp"

    Note

    This will only exclude paths below /var/*/tmp/, but not folders which are siblings of tmp; for example, /var/this-subfolder/tmp, but not /var/this-subfolder/log.

    mdatp exclusion folder add --path "/var/"

    OR

    mdatp exclusion folder add --path "/var/*/"

    Note

    This will exclude all paths whose parent is /var/; for example, /var/this-subfolder/and-this-subfolder-as-well.

    Folder exclusion configured successfully

  • Add an exclusion for a process:

    mdatp exclusion process add --name cat

    Process exclusion configured successfully

  • Add an exclusion for a second process:

    mdatp exclusion process add --name cat
mdatp exclusion process add --name dog

    Process exclusion configured successfully

Validate exclusions lists with the EICAR test file

You can validate that your exclusion lists are working by using curl to download a test file.

In the following Bash snippet, replace test.txt with a file that conforms to your exclusion rules. For example, if you have excluded the .testing extension, replace test.txt with test.testing. If you are testing a path, ensure that you run the command within that path.

curl -o test.txt https://www.eicar.org/download/eicar.com.txt

If Defender for Endpoint on Linux reports malware, then the rule is not working. If there is no report of malware, and the downloaded file exists, then the exclusion is working. You can open the file to confirm that the contents are the same as what is described on the EICAR test file website.

If you do not have Internet access, you can create your own EICAR test file. Write the EICAR string to a new text file with the following Bash command:

echo 'X5O!P%@AP[4\PZX54(P^)7CC)7}$EICAR-STANDARD-ANTIVIRUS-TEST-FILE!$H+H*' > test.txt

You can also copy the string into a blank text file and attempt to save it with the file name or in the folder you are attempting to exclude.

Allow threats

In addition to excluding certain content from being scanned, you can also configure the product not to detect some classes of threats (identified by the threat name). You should exercise caution when using this functionality, as it can leave your device unprotected.

To add a threat name to the allowed list, execute the following command:

mdatp threat allowed add --name [threat-name]

The threat name associated with a detection on your device can be obtained using the following command:

mdatp threat list

For example, to add EICAR-Test-File (not a virus) (the threat name associated with the EICAR detection) to the allowed list, execute the following command:

mdatp threat allowed add --name "EICAR-Test-File (not a virus)"