Exchange SSRF Autodiscover ProxyShell - Detection

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Id	968358d6-6af8-49bb-aaa4-187b3067fb95
Rulename	Exchange SSRF Autodiscover ProxyShell - Detection
Description	This query looks for suspicious request patterns to Exchange servers that fit patterns recently blogged about by PeterJson. This exploitation chain utilises an SSRF vulnerability in Exchange which eventually allows the attacker to execute arbitrary Powershell on the server. In the example powershell can be used to write an email to disk with an encoded attachment containing a shell. Reference: https://peterjson.medium.com/reproducing-the-proxyshell-pwn2own-exploit-49743a4ea9a1
Severity	High
Tactics	InitialAccess
Techniques	T1190
Required data connectors	AzureMonitor(IIS)
Kind	Scheduled
Query frequency	12h
Query period	12h
Trigger threshold	0
Trigger operator	gt
Source Uri	https://github.com/Azure/Azure-Sentinel/blob/master/Detections/W3CIISLog/ProxyShellPwn2Own.yaml
Version	1.0.3
Arm template	968358d6-6af8-49bb-aaa4-187b3067fb95.json

KQL

let successCodes = dynamic([200, 302, 401]);
W3CIISLog
| where scStatus has_any (successCodes)
| where ipv4_is_private(cIP) == False
| where csUriStem hasprefix "/autodiscover/autodiscover.json"
| project TimeGenerated, cIP, sIP, sSiteName, csUriStem, csUriQuery, Computer, csUserName, _ResourceId, FileUri
| where (csUriQuery !has "Protocol" and isnotempty(csUriQuery))
or (csUriQuery has_any("/mapi/", "powershell"))
or (csUriQuery contains "@" and csUriQuery matches regex @"\.[a-zA-Z]{2,4}?(?:[a-zA-Z]{2,4}\/)")
or (csUriQuery contains ":" and csUriQuery matches regex @"\:[0-9]{2,4}\/")
| extend HostName = tostring(split(Computer, ".")[0]), DomainIndex = toint(indexof(Computer, '.'))
| extend HostNameDomain = iff(DomainIndex != -1, substring(Computer, DomainIndex + 1), Computer)
| extend AccountName = tostring(split(csUserName, "@")[0]), AccountUPNSuffix = tostring(split(csUserName, "@")[1])

YAML

kind: Scheduled
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Detections/W3CIISLog/ProxyShellPwn2Own.yaml
query: |
  let successCodes = dynamic([200, 302, 401]);
  W3CIISLog
  | where scStatus has_any (successCodes)
  | where ipv4_is_private(cIP) == False
  | where csUriStem hasprefix "/autodiscover/autodiscover.json"
  | project TimeGenerated, cIP, sIP, sSiteName, csUriStem, csUriQuery, Computer, csUserName, _ResourceId, FileUri
  | where (csUriQuery !has "Protocol" and isnotempty(csUriQuery))
  or (csUriQuery has_any("/mapi/", "powershell"))
  or (csUriQuery contains "@" and csUriQuery matches regex @"\.[a-zA-Z]{2,4}?(?:[a-zA-Z]{2,4}\/)")
  or (csUriQuery contains ":" and csUriQuery matches regex @"\:[0-9]{2,4}\/")
  | extend HostName = tostring(split(Computer, ".")[0]), DomainIndex = toint(indexof(Computer, '.'))
  | extend HostNameDomain = iff(DomainIndex != -1, substring(Computer, DomainIndex + 1), Computer)
  | extend AccountName = tostring(split(csUserName, "@")[0]), AccountUPNSuffix = tostring(split(csUserName, "@")[1])  
requiredDataConnectors:
- dataTypes:
  - W3CIISLog
  connectorId: AzureMonitor(IIS)
tactics:
- InitialAccess
name: Exchange SSRF Autodiscover ProxyShell - Detection
metadata:
  source:
    kind: Community
  author:
    name: Thomas McElroy
  support:
    tier: Community
  categories:
    domains:
    - Security - Others
relevantTechniques:
- T1190
severity: High
entityMappings:
- fieldMappings:
  - identifier: FullName
    columnName: csUserName
  - identifier: Name
    columnName: AccountName
  - identifier: UPNSuffix
    columnName: AccountUPNSuffix
  entityType: Account
- fieldMappings:
  - identifier: FullName
    columnName: Computer
  entityType: Host
- fieldMappings:
  - identifier: Address
    columnName: cIP
  entityType: IP
- fieldMappings:
  - identifier: ResourceId
    columnName: _ResourceId
  entityType: AzureResource
queryFrequency: 12h
description: |
  'This query looks for suspicious request patterns to Exchange servers that fit patterns recently blogged about by PeterJson. This exploitation chain utilises an SSRF vulnerability in Exchange which eventually allows the attacker to execute arbitrary Powershell on the server.
  In the example powershell can be used to write an email to disk with an encoded attachment containing a shell.
  Reference: https://peterjson.medium.com/reproducing-the-proxyshell-pwn2own-exploit-49743a4ea9a1'  
triggerThreshold: 0
triggerOperator: gt
version: 1.0.3
queryPeriod: 12h
id: 968358d6-6af8-49bb-aaa4-187b3067fb95

ARM