Discord CDN Risky File Download ASIM Web Session Schema
Id | 01e8ffff-dc0c-43fe-aa22-d459c4204553 |
Rulename | Discord CDN Risky File Download (ASIM Web Session Schema) |
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. This analytic rule uses ASIM and supports any built-in or custom source that supports the ASIM WebSession schema (ASIM WebSession Schema) |
Severity | Medium |
Tactics | CommandAndControl |
Techniques | T1071.001 |
Required data connectors | SquidProxy Zscaler |
Kind | Scheduled |
Query frequency | 1d |
Query period | 1d |
Trigger threshold | 0 |
Trigger operator | gt |
Source Uri | https://github.com/Azure/Azure-Sentinel/blob/master/Detections/ASimWebSession/DiscordCDNRiskyFileDownload_ASim.yaml |
Version | 1.1.4 |
Arm template | 01e8ffff-dc0c-43fe-aa22-d459c4204553.json |
let discord=dynamic(["cdn.discordapp.com", "media.discordapp.com"]);
_Im_WebSession(url_has_any=discord, eventresult='Success')
| where Url has "attachments"
| extend DiscordServerId = extract(@"\/attachments\/([0-9]+)\/", 1, Url)
| summarize dcount(Url), make_set(SrcUsername), make_set(SrcIpAddr), make_set(Url), min(TimeGenerated), max(TimeGenerated), make_set(EventResult) by DiscordServerId
| mv-expand set_SrcUsername to typeof(string), set_Url to typeof(string), set_EventResult to typeof(string), set_SrcIpAddr to typeof(string)
| summarize by DiscordServerId, dcount_Url, set_SrcUsername, min_TimeGenerated, max_TimeGenerated, set_EventResult, set_SrcIpAddr, set_Url
| project StartTime=min_TimeGenerated, EndTime=max_TimeGenerated, Result=set_EventResult, SourceUser=set_SrcUsername, SourceIP=set_SrcIpAddr, RequestURL=set_Url
| where RequestURL has_any (".bin",".exe",".dll",".bin",".msi")
| extend AccountName = tostring(split(SourceUser, "@")[0]), AccountUPNSuffix = tostring(split(SourceUser, "@")[1])
id: 01e8ffff-dc0c-43fe-aa22-d459c4204553
name: Discord CDN Risky File Download (ASIM Web Session Schema)
tags:
- Discord
requiredDataConnectors:
- connectorId: SquidProxy
dataTypes:
- SquidProxy_CL
- connectorId: Zscaler
dataTypes:
- CommonSecurityLog
entityMappings:
- entityType: Account
fieldMappings:
- identifier: FullName
columnName: SourceUser
- identifier: Name
columnName: AccountName
- identifier: UPNSuffix
columnName: AccountUPNSuffix
- entityType: IP
fieldMappings:
- identifier: Address
columnName: SourceIP
- entityType: URL
fieldMappings:
- identifier: Url
columnName: RequestURL
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.
This analytic rule uses [ASIM](https://aka.ms/AboutASIM) and supports any built-in or custom source that supports the ASIM WebSession schema (ASIM WebSession Schema)'
query: |
let discord=dynamic(["cdn.discordapp.com", "media.discordapp.com"]);
_Im_WebSession(url_has_any=discord, eventresult='Success')
| where Url has "attachments"
| extend DiscordServerId = extract(@"\/attachments\/([0-9]+)\/", 1, Url)
| summarize dcount(Url), make_set(SrcUsername), make_set(SrcIpAddr), make_set(Url), min(TimeGenerated), max(TimeGenerated), make_set(EventResult) by DiscordServerId
| mv-expand set_SrcUsername to typeof(string), set_Url to typeof(string), set_EventResult to typeof(string), set_SrcIpAddr to typeof(string)
| summarize by DiscordServerId, dcount_Url, set_SrcUsername, min_TimeGenerated, max_TimeGenerated, set_EventResult, set_SrcIpAddr, set_Url
| project StartTime=min_TimeGenerated, EndTime=max_TimeGenerated, Result=set_EventResult, SourceUser=set_SrcUsername, SourceIP=set_SrcIpAddr, RequestURL=set_Url
| where RequestURL has_any (".bin",".exe",".dll",".bin",".msi")
| extend AccountName = tostring(split(SourceUser, "@")[0]), AccountUPNSuffix = tostring(split(SourceUser, "@")[1])
severity: Medium
triggerThreshold: 0
queryPeriod: 1d
queryFrequency: 1d
triggerOperator: gt
kind: Scheduled
tactics:
- CommandAndControl
relevantTechniques:
- T1071.001
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Detections/ASimWebSession/DiscordCDNRiskyFileDownload_ASim.yaml
version: 1.1.4
metadata:
author:
name: Microsoft Security Research
source:
kind: Community
categories:
domains:
- Security - Threat Protection
support:
tier: Community
{
"$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
"contentVersion": "1.0.0.0",
"parameters": {
"workspace": {
"type": "String"
}
},
"resources": [
{
"apiVersion": "2023-02-01-preview",
"id": "[concat(resourceId('Microsoft.OperationalInsights/workspaces/providers', parameters('workspace'), 'Microsoft.SecurityInsights'),'/alertRules/01e8ffff-dc0c-43fe-aa22-d459c4204553')]",
"kind": "Scheduled",
"name": "[concat(parameters('workspace'),'/Microsoft.SecurityInsights/01e8ffff-dc0c-43fe-aa22-d459c4204553')]",
"properties": {
"alertRuleTemplateName": "01e8ffff-dc0c-43fe-aa22-d459c4204553",
"customDetails": null,
"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. \n 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.\n This analytic rule uses [ASIM](https://aka.ms/AboutASIM) and supports any built-in or custom source that supports the ASIM WebSession schema (ASIM WebSession Schema)'\n",
"displayName": "Discord CDN Risky File Download (ASIM Web Session Schema)",
"enabled": true,
"entityMappings": [
{
"entityType": "Account",
"fieldMappings": [
{
"columnName": "SourceUser",
"identifier": "FullName"
},
{
"columnName": "AccountName",
"identifier": "Name"
},
{
"columnName": "AccountUPNSuffix",
"identifier": "UPNSuffix"
}
]
},
{
"entityType": "IP",
"fieldMappings": [
{
"columnName": "SourceIP",
"identifier": "Address"
}
]
},
{
"entityType": "URL",
"fieldMappings": [
{
"columnName": "RequestURL",
"identifier": "Url"
}
]
}
],
"OriginalUri": "https://github.com/Azure/Azure-Sentinel/blob/master/Detections/ASimWebSession/DiscordCDNRiskyFileDownload_ASim.yaml",
"query": "let discord=dynamic([\"cdn.discordapp.com\", \"media.discordapp.com\"]);\n _Im_WebSession(url_has_any=discord, eventresult='Success')\n | where Url has \"attachments\"\n | extend DiscordServerId = extract(@\"\\/attachments\\/([0-9]+)\\/\", 1, Url)\n | summarize dcount(Url), make_set(SrcUsername), make_set(SrcIpAddr), make_set(Url), min(TimeGenerated), max(TimeGenerated), make_set(EventResult) by DiscordServerId\n | mv-expand set_SrcUsername to typeof(string), set_Url to typeof(string), set_EventResult to typeof(string), set_SrcIpAddr to typeof(string)\n | summarize by DiscordServerId, dcount_Url, set_SrcUsername, min_TimeGenerated, max_TimeGenerated, set_EventResult, set_SrcIpAddr, set_Url\n | project StartTime=min_TimeGenerated, EndTime=max_TimeGenerated, Result=set_EventResult, SourceUser=set_SrcUsername, SourceIP=set_SrcIpAddr, RequestURL=set_Url\n | where RequestURL has_any (\".bin\",\".exe\",\".dll\",\".bin\",\".msi\")\n | extend AccountName = tostring(split(SourceUser, \"@\")[0]), AccountUPNSuffix = tostring(split(SourceUser, \"@\")[1])\n",
"queryFrequency": "P1D",
"queryPeriod": "P1D",
"severity": "Medium",
"suppressionDuration": "PT1H",
"suppressionEnabled": false,
"tactics": [
"CommandAndControl"
],
"tags": [
"Discord"
],
"techniques": [
"T1071"
],
"templateVersion": "1.1.4",
"triggerOperator": "GreaterThan",
"triggerThreshold": 0
},
"type": "Microsoft.OperationalInsights/workspaces/providers/alertRules"
}
]
}