Exchange Server Suspicious File Downloads
| Id | 8955c0fb-3408-47b0-a3b9-a1faec41e427 |
| Rulename | Exchange Server Suspicious File Downloads. |
| Description | This query looks for messages related to file downloads of suspicious file types on an Exchange Server. This could indicate attempted deployment of webshells. This query uses the Exchange HttpProxy AOBGeneratorLog, you will need to onboard this log as a custom log under the table http_proxy_oab_CL before using this query. This log is commonly found at C:\Program Files\Microsoft\Exchange Server\V15\Logging\OABGeneratorLog on the Exchange server. Details on collecting custom logs into Sentinel can be found here: https://learn.microsoft.com/azure/sentinel/connect-custom-logs |
| Severity | Medium |
| Tactics | InitialAccess |
| Techniques | T1190 |
| 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/http_proxy_oab_CL/ExchagngeSuspiciousFileDownloads.yaml |
| Version | 1.0.1 |
| Arm template | 8955c0fb-3408-47b0-a3b9-a1faec41e427.json |
let scriptExtensions = dynamic([".php", ".jsp", ".js", ".aspx", ".asmx", ".asax", ".cfm", ".shtml"]);
http_proxy_oab_CL
| where RawData contains "Download failed and temporary file"
| extend File = extract("([^\\\\]*)(\\\\[^']*)",2,RawData)
| extend Extension = strcat(".",split(File, ".")[-1])
| extend InteractiveFile = iif(Extension in (scriptExtensions), "Yes", "No")
// Uncomment the following line to alert only on interactive file download type
//| where InteractiveFile =~ "Yes"
| extend timestamp = TimeGenerated, HostCustomEntity = Computer
query: |
let scriptExtensions = dynamic([".php", ".jsp", ".js", ".aspx", ".asmx", ".asax", ".cfm", ".shtml"]);
http_proxy_oab_CL
| where RawData contains "Download failed and temporary file"
| extend File = extract("([^\\\\]*)(\\\\[^']*)",2,RawData)
| extend Extension = strcat(".",split(File, ".")[-1])
| extend InteractiveFile = iif(Extension in (scriptExtensions), "Yes", "No")
// Uncomment the following line to alert only on interactive file download type
//| where InteractiveFile =~ "Yes"
| extend timestamp = TimeGenerated, HostCustomEntity = Computer
name: Exchange Server Suspicious File Downloads.
requiredDataConnectors: []
entityMappings:
- entityType: Host
fieldMappings:
- identifier: FullName
columnName: HostCustomEntity
description: |
'This query looks for messages related to file downloads of suspicious file types on an Exchange Server. This could indicate attempted deployment of webshells.
This query uses the Exchange HttpProxy AOBGeneratorLog, you will need to onboard this log as a custom log under the table http_proxy_oab_CL before using this query.
This log is commonly found at C:\Program Files\Microsoft\Exchange Server\V15\Logging\OABGeneratorLog on the Exchange server. Details on collecting custom logs into Sentinel
can be found here: https://learn.microsoft.com/azure/sentinel/connect-custom-logs
kind: Scheduled
severity: Medium
triggerThreshold: 0
queryPeriod: 1d
queryFrequency: 1d
triggerOperator: gt
metadata:
author:
name: petebryan
source:
kind: Community
categories:
domains:
- Application
support:
tier: Community
tactics:
- InitialAccess
relevantTechniques:
- T1190
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Detections/http_proxy_oab_CL/ExchagngeSuspiciousFileDownloads.yaml
id: 8955c0fb-3408-47b0-a3b9-a1faec41e427
version: 1.0.1
{
"$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/8955c0fb-3408-47b0-a3b9-a1faec41e427')]",
"kind": "Scheduled",
"name": "[concat(parameters('workspace'),'/Microsoft.SecurityInsights/8955c0fb-3408-47b0-a3b9-a1faec41e427')]",
"properties": {
"alertRuleTemplateName": "8955c0fb-3408-47b0-a3b9-a1faec41e427",
"customDetails": null,
"description": "'This query looks for messages related to file downloads of suspicious file types on an Exchange Server. This could indicate attempted deployment of webshells. \nThis query uses the Exchange HttpProxy AOBGeneratorLog, you will need to onboard this log as a custom log under the table http_proxy_oab_CL before using this query. \nThis log is commonly found at C:\\Program Files\\Microsoft\\Exchange Server\\V15\\Logging\\OABGeneratorLog on the Exchange server. Details on collecting custom logs into Sentinel\ncan be found here: https://learn.microsoft.com/azure/sentinel/connect-custom-logs\n",
"displayName": "Exchange Server Suspicious File Downloads.",
"enabled": true,
"entityMappings": [
{
"entityType": "Host",
"fieldMappings": [
{
"columnName": "HostCustomEntity",
"identifier": "FullName"
}
]
}
],
"OriginalUri": "https://github.com/Azure/Azure-Sentinel/blob/master/Detections/http_proxy_oab_CL/ExchagngeSuspiciousFileDownloads.yaml",
"query": "let scriptExtensions = dynamic([\".php\", \".jsp\", \".js\", \".aspx\", \".asmx\", \".asax\", \".cfm\", \".shtml\"]);\nhttp_proxy_oab_CL\n| where RawData contains \"Download failed and temporary file\"\n| extend File = extract(\"([^\\\\\\\\]*)(\\\\\\\\[^']*)\",2,RawData)\n| extend Extension = strcat(\".\",split(File, \".\")[-1])\n| extend InteractiveFile = iif(Extension in (scriptExtensions), \"Yes\", \"No\")\n// Uncomment the following line to alert only on interactive file download type\n//| where InteractiveFile =~ \"Yes\"\n| extend timestamp = TimeGenerated, HostCustomEntity = Computer\n",
"queryFrequency": "P1D",
"queryPeriod": "P1D",
"severity": "Medium",
"suppressionDuration": "PT1H",
"suppressionEnabled": false,
"tactics": [
"InitialAccess"
],
"techniques": [
"T1190"
],
"templateVersion": "1.0.1",
"triggerOperator": "GreaterThan",
"triggerThreshold": 0
},
"type": "Microsoft.OperationalInsights/workspaces/providers/alertRules"
}
]
}