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varonis: add pre-processor option to allow ingestion of non-conformant CEF messages (elastic#13822)
Add a config option to add "pre-processors" which will run before the "decode_cef" processor on the agent. CEF messages from some sources may be malformed by not following the CEF spec exactly, which can then cause problems in the "decode_cef" processor. Having a pre-processor will allow running scripts that can correct the malformed CEF messages, and allow decode_cef to process them correctly. New test sample provided in issue from user.
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‎packages/varonis/_dev/build/docs/README.md‎

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This integration expects to use `External system default template (CEF)` for alert forwarding in Varonis DatAlert tool. In case any custom template is used, all the fields in `External system default template (CEF)` should also be present in custom template along with the other additional fields. Additional fields will be part of `varonis.logs` object and such fields will be indexed only if dynamic mapping is enabled in Elasticsearch.
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## Pre-Processors
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There are cases where incoming CEF messages do not follow the CEF specification exactly, and this can cause errors with
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message decoding. To work around this, there is an option for pre-processors, which are run before the CEF message is decoded.
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These can be used modify the message to follow the CEF specification correctly, which will allow proper decoding.
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The pre-processors will modify the `message` field before CEF decoding is done on the agent, but the original, non-preprocessed,
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message will still be preserved in the `event.original` field when the agent sends the event.
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## Logs reference
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### varonis.logs

‎packages/varonis/_dev/deploy/docker/docker-compose.yml‎

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volumes:
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- ./sample_logs:/sample_logs:ro
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command: log --start-signal=SIGHUP --delay=6s --addr elastic-agent:9031 -p=tcp /sample_logs/varonis.log
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varonis-udp-invalid-cef:
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image: docker.elastic.co/observability/stream:v0.15.0
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volumes:
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- ./sample_logs:/sample_logs:ro
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command: log --start-signal=SIGHUP --delay=6s --addr elastic-agent:9032 -p=udp /sample_logs/varonis_invalid_cef.log
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varonis-tcp-invalid-cef:
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image: docker.elastic.co/observability/stream:v0.15.0
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volumes:
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- ./sample_logs:/sample_logs:ro
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command: log --start-signal=SIGHUP --delay=6s --addr elastic-agent:9033 -p=tcp /sample_logs/varonis_invalid_cef.log

‎packages/varonis/_dev/deploy/docker/sample_logs/varonis_invalid_cef.log‎

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<14>Apr 28 15:59:01 VARONISSRVR1 CEF:0|Varonis Inc.|DatAdvantage|8.7.1|5015|DS object permission added|3|rt=Apr 28 2025 15:01:42 cat=Alert cs2=Permission changes on OU cs2Label=RuleName cn1=142 cn1Label=RuleID end=Apr 28 2025 14:53:02 duser=contosofoo.com\Bourne Jr., Jason dhost=AD-contosofoo.com filePath=contosofoo.com\Home Office Site\Computers\Containered fname=Containered act=DS object permission added dvchost=Compute outcome=Success msg=Permissions were added to "Containered" for group "contosofoo.com\Group Admins-Region_200" cs3= cs3Label=AttachmentName cs4= cs4Label=ClientAccessType deviceCustomDate1= fileType= cs1= cs1Label=MailRecipient suser= cs5= cs5Label=MailboxAccessType cnt= cs6= cs6Label=ChangedPermissions oldFilePermission= filePermission=Write dpriv=contosofoo.com\Group Admins-Region_200 start=Apr 28 2025 14:53:02
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<14>Apr 28 15:59:02 VARONISSRVR1 CEF:0|Varonis Inc.|DatAdvantage|8.7.1|5015|DS object permission added|3|rt=Apr 28 2025 15:01:42 cat=Alert cs2=Permission changes on OU cs2Label=RuleName cn1=142 cn1Label=RuleID end=Apr 28 2025 14:53:04 duser=contosofoo.com\Bourne Jr., Jason dhost=AD-contosofoo.com filePath=contosofoo.com\Home Office Site\Computers\Containered fname=Containered act=DS object permission added dvchost=Compute outcome=Success msg=Permissions were added to "Containered" for group "contosofoo.com\Group Admins-Region_200" cs3= cs3Label=AttachmentName cs4= cs4Label=ClientAccessType deviceCustomDate1= fileType= cs1= cs1Label=MailRecipient suser= cs5= cs5Label=MailboxAccessType cnt= cs6= cs6Label=ChangedPermissions oldFilePermission= filePermission=Write dpriv=contosofoo.com\Group Admins-Region_200 start=Apr 28 2025 14:53:03

‎packages/varonis/changelog.yml‎

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- version: "0.2.0"
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changes:
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- description: Add preprocessors config option, to allow running processors before CEF messages are decoded.
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type: enhancement
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link: https://github.com/elastic/integrations/pull/13822
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- version: "0.1.0"
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changes:
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- description: Initial release.

‎packages/varonis/data_stream/logs/_dev/test/system/test-tcp-invalid-cef-config.yml‎

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service: varonis-tcp-invalid-cef
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service_notify_signal: SIGHUP
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input: tcp
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data_stream:
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vars:
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tcp_host: 0.0.0.0
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tcp_port: 9033
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preserve_original_event: true
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tags:
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- forwarded
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preprocessors: |
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- script:
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lang: javascript
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description: Escape backslash characters.
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source: >
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function process(event) {
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var m = event.Get("message");
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event.Put("message", m.replace(/\\/g, "\\\\"));
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return event;
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}
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function test() {
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if ("\\".replace(/\\/g, "\\\\") !== "\\\\") {
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throw "expected replace \\ to \\\\ failed";
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}
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}
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assert:
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- hit_count: 2

‎packages/varonis/data_stream/logs/_dev/test/system/test-udp-invalid-cef-config.yml‎

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service: varonis-udp-invalid-cef
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service_notify_signal: SIGHUP
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input: udp
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data_stream:
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vars:
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udp_host: 0.0.0.0
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udp_port: 9032
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preserve_original_event: true
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tags:
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- forwarded
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preprocessors: |
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- script:
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lang: javascript
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description: Escape backslash characters.
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source: >
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function process(event) {
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var m = event.Get("message");
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event.Put("message", m.replace(/\\/g, "\\\\"));
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return event;
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}
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function test() {
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if ("\\".replace(/\\/g, "\\\\") !== "\\\\") {
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throw "expected replace \\ to \\\\ failed";
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}
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}
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assert:
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- hit_count: 2

‎packages/varonis/data_stream/logs/agent/stream/tcp.yml.hbs‎

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{{/contains}}
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processors:
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{{#if preprocessors}}
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- copy_fields:
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fields:
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- from: "message"
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to: "@metadata.event_original"
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{{preprocessors}}
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{{/if}}
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- rename:
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fields:
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- {from: "message", to: "event.original"}
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- decode_cef:
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field: event.original
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{{#if preprocessors}}
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- convert:
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mode: rename
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fields:
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- from: "@metadata.event_original"
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to: "event.original"
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{{/if}}
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{{#if processors}}
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{{processors}}
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{{/if}}

‎packages/varonis/data_stream/logs/agent/stream/udp.yml.hbs‎

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{{/contains}}
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processors:
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{{#if preprocessors}}
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- copy_fields:
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fields:
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- from: "message"
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to: "@metadata.event_original"
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{{preprocessors}}
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{{/if}}
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- rename:
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fields:
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- {from: "message", to: "event.original"}
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- decode_cef:
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field: event.original
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{{#if preprocessors}}
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- convert:
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mode: rename
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fields:
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- from: "@metadata.event_original"
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to: "event.original"
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{{/if}}
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{{#if processors}}
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{{processors}}
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{{/if}}

‎packages/varonis/data_stream/logs/fields/fields.yml‎

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- name: device_event_category
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type: keyword
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description: The category of the device event.
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- name: device_host_name
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type: keyword
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description: The host name of the device.
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- name: device_receipt_time
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description: The time the device received the event.
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- name: base_event_count

‎packages/varonis/data_stream/logs/manifest.yml‎

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default:
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- cef
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- forwarded
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- name: preprocessors
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title: Pre-Processors
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type: yaml
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description: >
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Pre-processors are run before the CEF message is decoded. They can be used to correct CEF formatting inconsistencies that may exist from some sources.
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See [Processors](https://www.elastic.co/guide/en/beats/filebeat/current/filtering-and-enhancing-data.html) for details.
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required: false
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show_user: false
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multi: false
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- name: processors
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type: yaml
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title: Processors
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default:
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- cef
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- forwarded
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- name: preprocessors
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title: Pre-Processors
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type: yaml
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description: >
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Pre-processors are run before the CEF message is decoded. They can be used to correct CEF formatting inconsistencies that may exist from some sources.
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See [Processors](https://www.elastic.co/guide/en/beats/filebeat/current/filtering-and-enhancing-data.html) for details.
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required: false
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show_user: false
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multi: false
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- name: processors
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type: yaml
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title: Processors

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