Detect potential presence of a malicious file with a double extension ASIM Web Session
Id | 6a71687f-00cf-44d3-93fc-8cbacc7b5615 |
Rulename | Detect potential presence of a malicious file with a double extension (ASIM Web Session) |
Description | Double extension vulnerability is a significant concern in file uploads, as it can lead to various issues if an attacker successfully uploads a virus-infected file. |
Severity | Medium |
Tactics | DefenseEvasion Persistence CommandAndControl |
Techniques | T1036 T1505 T1071 |
Kind | Scheduled |
Query frequency | 1h |
Query period | 1h |
Trigger threshold | 0 |
Trigger operator | gt |
Source Uri | https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Web Session Essentials/Analytic Rules/PossibleMaliciousDoubleExtension.yaml |
Version | 1.0.0 |
Arm template | 6a71687f-00cf-44d3-93fc-8cbacc7b5615.json |
let common_file_ext_list = dynamic([".txt", ".xlsx", ".doc", ".docx", ".csv", ".pdf", ".png", ".jpg", ".jpeg"]); // Add list of common files as per your environment
_Im_WebSession (starttime=ago(1h), eventresult='Success')
| where HttpRequestMethod in~ ("POST", "PUT")
| project
Url,
SrcIpAddr,
SrcUsername,
SrcHostname,
DstIpAddr,
DstPortNumber,
DstHostname,
TimeGenerated
| extend requestedFileName=tostring(split(tostring(parse_url(Url)["Path"]), '/')[-1])
| extend FileWithdualextension = extract(@'([\w-]+\.\w+\.\w+)$', 1, requestedFileName, typeof(string))
| extend SecondExt = tostring(split(FileWithdualextension, '.')[-1])
| where strcat('.', SecondExt) in~ (common_file_ext_list) // Second extension is mostly from the common files
| summarize
EventCount=count(),
EventStartTime=min(TimeGenerated),
EventEndTime=max(TimeGenerated)
by
SrcIpAddr,
Url,
FileWithdualextension,
SrcUsername,
SrcHostname,
DstIpAddr,
DstPortNumber,
DstHostname
| extend Name = iif(SrcUsername contains "@", tostring(split(SrcUsername,'@',0)[0]),SrcUsername), UPNSuffix = iif(SrcUsername contains "@",tostring(split(SrcUsername,'@',1)[0]),"")
customDetails:
EventStartTime: EventStartTime
DstHostname: DstHostname
EventCount: EventCount
EventEndTime: EventEndTime
triggerOperator: gt
queryFrequency: 1h
description: |
'Double extension vulnerability is a significant concern in file uploads, as it can lead to various
issues if an attacker successfully uploads a virus-infected file.'
alertDetailsOverride:
alertDescriptionFormat: User posted file '{{FileWithdualextension}}' which potentially contain dual extensions. This type of activity could be malicious and performed to bypass file upload filters or security measures implemented by the application. Destination server name this request was targetted to - '{{DstHostname}}'
alertDisplayNameFormat: User '{{SrcUsername}}' with IP address '{{SrcIpAddr}}' has been observed with posting potentially risky dual extension file
status: Available
kind: Scheduled
triggerThreshold: 0
requiredDataConnectors: []
version: 1.0.0
eventGroupingSettings:
aggregationKind: AlertPerResult
queryPeriod: 1h
name: Detect potential presence of a malicious file with a double extension (ASIM Web Session)
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Web Session Essentials/Analytic Rules/PossibleMaliciousDoubleExtension.yaml
id: 6a71687f-00cf-44d3-93fc-8cbacc7b5615
tags:
- Schema: WebSession
SchemaVersion: 0.2.6
tactics:
- DefenseEvasion
- Persistence
- CommandAndControl
relevantTechniques:
- T1036
- T1505
- T1071
severity: Medium
entityMappings:
- fieldMappings:
- identifier: Name
columnName: FileWithdualextension
entityType: File
- fieldMappings:
- identifier: Url
columnName: Url
entityType: URL
- fieldMappings:
- identifier: Address
columnName: SrcIpAddr
entityType: IP
- fieldMappings:
- identifier: Name
columnName: Name
- identifier: UPNSuffix
columnName: UPNSuffix
entityType: Account
- fieldMappings:
- identifier: HostName
columnName: SrcHostname
entityType: Host
query: |
let common_file_ext_list = dynamic([".txt", ".xlsx", ".doc", ".docx", ".csv", ".pdf", ".png", ".jpg", ".jpeg"]); // Add list of common files as per your environment
_Im_WebSession (starttime=ago(1h), eventresult='Success')
| where HttpRequestMethod in~ ("POST", "PUT")
| project
Url,
SrcIpAddr,
SrcUsername,
SrcHostname,
DstIpAddr,
DstPortNumber,
DstHostname,
TimeGenerated
| extend requestedFileName=tostring(split(tostring(parse_url(Url)["Path"]), '/')[-1])
| extend FileWithdualextension = extract(@'([\w-]+\.\w+\.\w+)$', 1, requestedFileName, typeof(string))
| extend SecondExt = tostring(split(FileWithdualextension, '.')[-1])
| where strcat('.', SecondExt) in~ (common_file_ext_list) // Second extension is mostly from the common files
| summarize
EventCount=count(),
EventStartTime=min(TimeGenerated),
EventEndTime=max(TimeGenerated)
by
SrcIpAddr,
Url,
FileWithdualextension,
SrcUsername,
SrcHostname,
DstIpAddr,
DstPortNumber,
DstHostname
| extend Name = iif(SrcUsername contains "@", tostring(split(SrcUsername,'@',0)[0]),SrcUsername), UPNSuffix = iif(SrcUsername contains "@",tostring(split(SrcUsername,'@',1)[0]),"")
{
"$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/6a71687f-00cf-44d3-93fc-8cbacc7b5615')]",
"kind": "Scheduled",
"name": "[concat(parameters('workspace'),'/Microsoft.SecurityInsights/6a71687f-00cf-44d3-93fc-8cbacc7b5615')]",
"properties": {
"alertDetailsOverride": {
"alertDescriptionFormat": "User posted file '{{FileWithdualextension}}' which potentially contain dual extensions. This type of activity could be malicious and performed to bypass file upload filters or security measures implemented by the application. Destination server name this request was targetted to - '{{DstHostname}}'",
"alertDisplayNameFormat": "User '{{SrcUsername}}' with IP address '{{SrcIpAddr}}' has been observed with posting potentially risky dual extension file"
},
"alertRuleTemplateName": "6a71687f-00cf-44d3-93fc-8cbacc7b5615",
"customDetails": {
"DstHostname": "DstHostname",
"EventCount": "EventCount",
"EventEndTime": "EventEndTime",
"EventStartTime": "EventStartTime"
},
"description": "'Double extension vulnerability is a significant concern in file uploads, as it can lead to various \n issues if an attacker successfully uploads a virus-infected file.'\n",
"displayName": "Detect potential presence of a malicious file with a double extension (ASIM Web Session)",
"enabled": true,
"entityMappings": [
{
"entityType": "File",
"fieldMappings": [
{
"columnName": "FileWithdualextension",
"identifier": "Name"
}
]
},
{
"entityType": "URL",
"fieldMappings": [
{
"columnName": "Url",
"identifier": "Url"
}
]
},
{
"entityType": "IP",
"fieldMappings": [
{
"columnName": "SrcIpAddr",
"identifier": "Address"
}
]
},
{
"entityType": "Account",
"fieldMappings": [
{
"columnName": "Name",
"identifier": "Name"
},
{
"columnName": "UPNSuffix",
"identifier": "UPNSuffix"
}
]
},
{
"entityType": "Host",
"fieldMappings": [
{
"columnName": "SrcHostname",
"identifier": "HostName"
}
]
}
],
"eventGroupingSettings": {
"aggregationKind": "AlertPerResult"
},
"OriginalUri": "https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Web Session Essentials/Analytic Rules/PossibleMaliciousDoubleExtension.yaml",
"query": "let common_file_ext_list = dynamic([\".txt\", \".xlsx\", \".doc\", \".docx\", \".csv\", \".pdf\", \".png\", \".jpg\", \".jpeg\"]); // Add list of common files as per your environment\n_Im_WebSession (starttime=ago(1h), eventresult='Success')\n| where HttpRequestMethod in~ (\"POST\", \"PUT\") \n| project\n Url,\n SrcIpAddr,\n SrcUsername,\n SrcHostname,\n DstIpAddr,\n DstPortNumber,\n DstHostname,\n TimeGenerated\n| extend requestedFileName=tostring(split(tostring(parse_url(Url)[\"Path\"]), '/')[-1])\n| extend FileWithdualextension = extract(@'([\\w-]+\\.\\w+\\.\\w+)$', 1, requestedFileName, typeof(string))\n| extend SecondExt = tostring(split(FileWithdualextension, '.')[-1])\n| where strcat('.', SecondExt) in~ (common_file_ext_list) // Second extension is mostly from the common files\n| summarize\n EventCount=count(),\n EventStartTime=min(TimeGenerated),\n EventEndTime=max(TimeGenerated)\n by\n SrcIpAddr,\n Url,\n FileWithdualextension,\n SrcUsername,\n SrcHostname,\n DstIpAddr,\n DstPortNumber,\n DstHostname\n| extend Name = iif(SrcUsername contains \"@\", tostring(split(SrcUsername,'@',0)[0]),SrcUsername), UPNSuffix = iif(SrcUsername contains \"@\",tostring(split(SrcUsername,'@',1)[0]),\"\")\n",
"queryFrequency": "PT1H",
"queryPeriod": "PT1H",
"severity": "Medium",
"status": "Available",
"suppressionDuration": "PT1H",
"suppressionEnabled": false,
"tactics": [
"CommandAndControl",
"DefenseEvasion",
"Persistence"
],
"tags": [
{
"Schema": "WebSession",
"SchemaVersion": "0.2.6"
}
],
"techniques": [
"T1036",
"T1071",
"T1505"
],
"templateVersion": "1.0.0",
"triggerOperator": "GreaterThan",
"triggerThreshold": 0
},
"type": "Microsoft.OperationalInsights/workspaces/providers/alertRules"
}
]
}