Discord CDN Risky File Download

Back


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

queryPeriod: 1d
kind: Scheduled
entityMappings:
- entityType: Account
  fieldMappings:
  - identifier: FullName
    columnName: SourceUser
- entityType: IP
  fieldMappings:
  - identifier: Address
    columnName: SourceIP
- entityType: URL
  fieldMappings:
  - identifier: Url
    columnName: RequestURL
requiredDataConnectors:
- connectorId: CefAma
  dataTypes:
  - CommonSecurityLog
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'
queryFrequency: 1d
triggerOperator: gt
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)  
name: Discord CDN Risky File Download
id: 010bd98c-a6be-498c-bdcd-502308c0fdae
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Zscaler Internet Access/Analytic Rules/DiscordCDNRiskyDownload.yaml
severity: Medium
version: 1.0.4
status: Available
relevantTechniques:
- T1071.001
tags:
- Discord
triggerThreshold: 0
tactics:
- CommandAndControl

ARM