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[RFC] Stage 0: Introducing new fields in file/dll/process fields (ela…
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…stic#2387)


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Co-authored-by: Michael Wolf <[email protected]>
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AsuNa-jp and mjwolf authored Oct 15, 2024
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# 0048: File Origin Fields
<!-- Leave this ID at 0000. The ECS team will assign a unique, contiguous RFC number upon merging the initial stage of this RFC. -->

- Stage: **0 (strawperson)** <!-- Update to reflect target stage. See https://elastic.github.io/ecs/stages.html -->
- Date: **2024-10-15** <!-- The ECS team sets this date at merge time. This is the date of the latest stage advancement. -->

<!--
As you work on your RFC, use the "Stage N" comments to guide you in what you should focus on, for the stage you're targeting.
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<!--
Stage 0: Provide a high level summary of the premise of these changes. Briefly describe the nature, purpose, and impact of the changes. ~2-5 sentences.
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It is known that when downloading files from the internet using a web browser (eg. Chrome, Edge, etc), information about the file's source is added to the file.
In Windows, it is known as the Mark of the Web and stored in file's Alternate Data Stream (ADS). In MacOS, it is stored in file's extended file attributes (metadata).

For example, in Windows, when you download an image file (`image17.webp`) from [this webpage](https://www.elastic.co/security-labs/pikabot-i-choose-you) using a web browser, the download source URL is automatically added to the file's Alternate Data Stream (ADS) as following.

<img width="578" alt="image" src="https://github.com/user-attachments/assets/b3dba571-1155-4226-88a0-fb9d67424d64">

* Inside `image17.webp:Zone.Identifier:$DATA`
<img width="804" alt="image" src="https://github.com/user-attachments/assets/f6058d40-d060-4dcb-9bdc-760e76389b45">

In ensuring endpoint security, the origin information of a file is crucial for determining whether a downloaded file or executable from the internet comes from a safe source and if it is safe to execute.

Thus, this PR adds new fields to store the URL of the file's origin information for `file`, `process`, and `dll`.
The ReferrerUrl is intended to be stored in the `origin_referrer_url` field, and the `HostUrl` is inteded to be stored in the `origin_url` field. The ZoneId is intended to be stored in the `zone_identifier` field.

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## Fields

<!--
Stage 1: Describe at a high level how this change affects fields. Include new or updated yml field definitions for all of the essential fields in this draft. While not exhaustive, the fields documented here should be comprehensive enough to deeply evaluate the technical considerations of this change. The goal here is to validate the technical details for all essential fields and to provide a basis for adding experimental field definitions to the schema. Use GitHub code blocks with yml syntax formatting, and add them to the corresponding RFC folder.
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The new fields proposed are:

Field | Type | Description /Usage
-- | -- | --
file.origin_referrer_url | keyword | The URL of the webpage that linked to the file.
file.origin_url | keyword | The URL where the file is hosted.
file.zone_identifier | short | Numerical identifier that indicates the security zone of a file's origin.
process.origin_referrer_url | keyword | The URL of the webpage that linked to the file.
process.origin_url | keyword | The URL where the file is hosted.
process.zone_identifier | short | Numerical identifier that indicates the security zone of a file's origin.
dll.origin_referrer_url | keyword | The URL of the webpage that linked to the file.
dll.origin_url | keyword | The URL where the file is hosted.
dll.zone_identifier | short | Numerical identifier that indicates the security zone of a file's origin.

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## Usage

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Stage 1: Describe at a high-level how these field changes will be used in practice. Real world examples are encouraged. The goal here is to understand how people would leverage these fields to gain insights or solve problems. ~1-3 paragraphs.
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## Source data

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## Scope of impact

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## Concerns

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## People

The following are the people that consulted on the contents of this RFC.

* @AsuNa-jp | author
* @joe-desimone
* @trisch-me
* @mjwolf

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## References

<!-- Insert any links appropriate to this RFC in this section. -->


### RFC Pull Requests

<!-- An RFC should link to the PRs for each of it stage advancements. -->

* Stage 0: https://github.com/elastic/ecs/pull/2387

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