Discord CDN Risky File Download

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Id	010bd98c-a6be-498c-bdcd-502308c0fdae
Rulename	Discord CDN Risky File Download
Description	Identifies callouts to Discord CDN addresses for risky file extensions. This detection will trigger when a callout for a risky file is made to a discord server that has only been seen once in your environment. Unique discord servers are identified using the server ID that is included in the request URL (DiscordServerId in query). Discord CDN has been used in multiple campaigns to download additional payloads
Severity	Medium
Tactics	CommandAndControl
Techniques	T1071.001
Required data connectors	CefAma
Kind	Scheduled
Query frequency	1d
Query period	1d
Trigger threshold	0
Trigger operator	gt
Source Uri	https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Zscaler Internet Access/Analytic Rules/DiscordCDNRiskyDownload.yaml
Version	1.0.4
Arm template	010bd98c-a6be-498c-bdcd-502308c0fdae.json

KQL

let connectionThreshold = 1;
let riskyExtensions = dynamic([".bin",".exe",".dll",".bin",".msi"]);
CommonSecurityLog
| where DeviceVendor =~ "ZScaler"
| where RequestURL has_any("media.discordapp.net", "cdn.discordapp.com")
| where RequestURL has "attachments"
| where DeviceAction !~ "blocked"
| extend DiscordServerId = extract(@"\/attachments\/([0-9]+)\/", 1, RequestURL)
| summarize dcount(RequestURL), make_set(SourceUserName), make_set(SourceIP), make_set(RequestURL), min(TimeGenerated), max(TimeGenerated), make_set(DeviceAction) by DiscordServerId, DeviceProduct
| where dcount_RequestURL <= connectionThreshold
| mv-expand set_SourceUserName to typeof(string), set_RequestURL to typeof(string), set_DeviceAction to typeof(string), set_SourceIP to typeof(string)
| summarize by DiscordServerId, DeviceProduct, dcount_RequestURL, set_SourceUserName, min_TimeGenerated, max_TimeGenerated, set_DeviceAction, set_SourceIP, set_RequestURL
| project StartTime=min_TimeGenerated, EndTime=max_TimeGenerated, DeviceActionTaken=set_DeviceAction, DeviceProduct, SourceUser=set_SourceUserName, SourceIP=set_SourceIP, RequestURL=set_RequestURL
| where RequestURL has_any (riskyExtensions)

YAML

kind: Scheduled
queryFrequency: 1d
queryPeriod: 1d
status: Available
tactics:
- CommandAndControl
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Zscaler Internet Access/Analytic Rules/DiscordCDNRiskyDownload.yaml
version: 1.0.4
triggerThreshold: 0
description: |
    'Identifies callouts to Discord CDN addresses for risky file extensions. This detection will trigger when a callout for a risky file is made to a discord server that has only been seen once in your environment. Unique discord servers are identified using the server ID that is included in the request URL (DiscordServerId in query). Discord CDN has been used in multiple campaigns to download additional payloads'
severity: Medium
relevantTechniques:
- T1071.001
id: 010bd98c-a6be-498c-bdcd-502308c0fdae
name: Discord CDN Risky File Download
query: |
  let connectionThreshold = 1;
  let riskyExtensions = dynamic([".bin",".exe",".dll",".bin",".msi"]);
  CommonSecurityLog
  | where DeviceVendor =~ "ZScaler"
  | where RequestURL has_any("media.discordapp.net", "cdn.discordapp.com")
  | where RequestURL has "attachments"
  | where DeviceAction !~ "blocked"
  | extend DiscordServerId = extract(@"\/attachments\/([0-9]+)\/", 1, RequestURL)
  | summarize dcount(RequestURL), make_set(SourceUserName), make_set(SourceIP), make_set(RequestURL), min(TimeGenerated), max(TimeGenerated), make_set(DeviceAction) by DiscordServerId, DeviceProduct
  | where dcount_RequestURL <= connectionThreshold
  | mv-expand set_SourceUserName to typeof(string), set_RequestURL to typeof(string), set_DeviceAction to typeof(string), set_SourceIP to typeof(string)
  | summarize by DiscordServerId, DeviceProduct, dcount_RequestURL, set_SourceUserName, min_TimeGenerated, max_TimeGenerated, set_DeviceAction, set_SourceIP, set_RequestURL
  | project StartTime=min_TimeGenerated, EndTime=max_TimeGenerated, DeviceActionTaken=set_DeviceAction, DeviceProduct, SourceUser=set_SourceUserName, SourceIP=set_SourceIP, RequestURL=set_RequestURL
  | where RequestURL has_any (riskyExtensions)  
requiredDataConnectors:
- dataTypes:
  - CommonSecurityLog
  connectorId: CefAma
tags:
- Discord
entityMappings:
- fieldMappings:
  - identifier: FullName
    columnName: SourceUser
  entityType: Account
- fieldMappings:
  - identifier: Address
    columnName: SourceIP
  entityType: IP
- fieldMappings:
  - identifier: Url
    columnName: RequestURL
  entityType: URL
triggerOperator: gt

ARM