Path Interception by PATH Environment Variable

let SuspiciousPathChanges = DeviceRegistryEvents
| where Timestamp > ago(24h)
| where RegistryKey has "Environment"
| where RegistryValueName in~ ("PATH", "Path", "windir", "SystemRoot", "TEMP", "TMP")
| where not(InitiatingProcessFileName in~ ("msiexec.exe", "setup.exe", "svchost.exe", "services.exe"))
| project Timestamp, DeviceName, AccountName, RegistryKey, RegistryValueName, RegistryValueData, InitiatingProcessFileName;
SuspiciousPathChanges
| join kind=leftouter (
    DeviceProcessEvents
    | where Timestamp > ago(24h)
    | where FolderPath !has "C:\\Windows\\"
    | where FolderPath !has "C:\\Program Files"
    | project DeviceId, ProcessId, FileName, FolderPath, AccountName
) on DeviceId
| project Timestamp, DeviceName, AccountName, RegistryKey, RegistryValueName, RegistryValueData, InitiatingProcessFileName
| sort by Timestamp desc

index=wineventlog sourcetype="XmlWinEventLog:Microsoft-Windows-Sysmon/Operational" EventCode=13
| where TargetObject like "%\\Environment\\Path" OR TargetObject like "%\\Environment\\windir" OR TargetObject like "%\\Environment\\SystemRoot"
| where NOT (Image like "%msiexec.exe" OR Image like "%setup.exe" OR Image like "%services.exe" OR Image like "%svchost.exe")
| eval SuspiciousValue=if(
    match(lower(Details), "(temp|appdata|public|users\\\\|programdata)"),
    1, 0)
| table _time, host, User, TargetObject, Details, Image, SuspiciousValue
| sort - _time

registry where event.type in ("creation", "change")
  and registry.path : ("*\\Environment\\PATH", "*\\Environment\\windir", "*\\Environment\\SystemRoot")
  and not process.name : ("msiexec.exe", "setup.exe", "svchost.exe")

SELECT
  DATEFORMAT(devicetime,'yyyy-MM-dd HH:mm:ss') AS EventTime,
  sourceip AS HostIP, username,
  "CommandLine", "Image" AS ProcessImage,
  "TargetFilename" AS ModifiedFile,
  CASE
    WHEN "TargetFilename" ILIKE '%\\temp\\%.exe' AND eventid = 11 THEN 90
    WHEN "TargetFilename" ILIKE '%\\temp\\%.dll' AND eventid = 11 THEN 80
    ELSE 50
  END AS RiskScore,
  CASE
    WHEN eventid = 11 AND "TargetFilename" ILIKE '%\\temp\\%.exe' THEN 'EXE Created in Temp'
    WHEN eventid = 1 AND "Image" ILIKE '%\\temp\\%' THEN 'Elevated Execution from Temp'
    ELSE 'Suspicious File Activity'
  END AS AlertType
FROM events
WHERE eventid IN (1, 11)
  AND ("Image" ILIKE '%\\temp\\%' OR "TargetFilename" ILIKE '%\\temp\\%')
  AND ("Image" ILIKE '%.exe%' OR "TargetFilename" ILIKE '%.exe' OR "TargetFilename" ILIKE '%.dll')
  AND username NOT ILIKE '%SYSTEM%'
  AND username NOT ILIKE '%TrustedInstaller%'
  AND LOGSOURCETYPENAME(devicetype) ILIKE '%sysmon%'
ORDER BY RiskScore DESC
LAST 24 HOURS

_sourceCategory=*sysmon*
| json auto
| where EventCode in ("1","11")
| eval FilePath = if(EventCode = "1", Image, TargetFilename)
| where matches(lower(FilePath), "\\temp\\")
| where matches(lower(FilePath), "(\.exe|\.dll)$")
| eval IsInstaller = if(EventCode = "1" and matches(lower(Image), "(setup|install|msiexec|update)"), "true", "false")
| eval IsBinaryCreate = if(EventCode = "11", "true", "false")
| where User != "NT AUTHORITY\SYSTEM" and !isNull(User)
| eval RiskScore = if(IsInstaller = "true" or IsBinaryCreate = "true", 75, 40)
| stats values(EventCode) AS EventTypes, values(FilePath) AS Files, count AS EventCount by _sourceHost, User, _timeslice 10m
| where EventCount > 1
| sort by EventCount desc

rule T1574_007_hijack_execution {
  meta:
    author = "Detection Engineering"
    description = "Detects execution flow hijacking via installer or DLL path manipulation"
    severity = "high"
    confidence = "medium"
    mitre_attack = "T1574.007"
    reference = "https://attack.mitre.org/techniques/T1574/007/"

  events:
    $e.metadata.event_type = "PROCESS_LAUNCH"
    (
      re.regex($e.target.process.file.full_path, `(?i)\\temp\\.*\.exe`) or
      re.regex($e.target.process.file.full_path, `(?i)\\appdata\\.*\.exe`)
    )
    not re.regex($e.principal.process.file.full_path, `(?i)(msiexec|trustedinstaller|wusa|dpinst)`)
    not $e.principal.user.user_display_name = "SYSTEM"

  condition:
    $e
}

#event_simpleName in ("ProcessRollup2", "SyntheticProcessRollup2")
| ImageFileName = /(?i)\\temp\\.*\.exe/
| ParentBaseFileName != /(?i)(msiexec|trustedinstaller|wusa|dpinst|svchost)/
| UserName != "SYSTEM"
| UserName != ""
| groupBy([aid, ComputerName, ImageFileName, ParentBaseFileName, UserName, CommandLine], function=[count(as=EventCount), min(timestamp, as=FirstSeen)])
| case {
    ImageFileName = /(?i)\\temp\\/i AND ParentBaseFileName = /(?i)(setup|install|update)/ => RiskScore := "High";
    ImageFileName = /(?i)\\temp\\/i => RiskScore := "Medium";
    * => RiskScore := "Low";
  }
| where RiskScore in ("High", "Medium")
| table([ComputerName, UserName, ImageFileName, ParentBaseFileName, CommandLine, EventCount, RiskScore, FirstSeen])
| sort(RiskScore)