Path Interception by Search Order Hijacking

let SystemBinaryNames = dynamic([
  "net.exe", "cmd.exe", "powershell.exe", "ping.exe",
  "ipconfig.exe", "whoami.exe", "hostname.exe", "nltest.exe",
  "tasklist.exe", "sc.exe", "reg.exe", "certutil.exe"
]);
DeviceProcessEvents
| where Timestamp > ago(24h)
| where FileName in~ (SystemBinaryNames)
| where not(FolderPath startswith "C:\\Windows\\system32")
| where not(FolderPath startswith "C:\\Windows\\SysWOW64")
| where not(FolderPath startswith "C:\\Windows\\WinSxS")
| project Timestamp, DeviceName, AccountName, FileName, FolderPath,
         ProcessCommandLine, InitiatingProcessFileName, InitiatingProcessFolderPath
| sort by Timestamp desc

index=wineventlog sourcetype="XmlWinEventLog:Microsoft-Windows-Sysmon/Operational" EventCode=1
| eval BinaryName=lower(mvindex(split(Image, "\\"), -1))
| eval IsSystemBinary=if(
    BinaryName in ("net.exe", "cmd.exe", "powershell.exe", "ping.exe", "ipconfig.exe",
                   "whoami.exe", "hostname.exe", "nltest.exe", "tasklist.exe",
                   "sc.exe", "reg.exe", "certutil.exe", "net1.exe"),
    1, 0)
| eval IsSystemPath=if(
    match(lower(Image), "(c:\\\\windows\\\\system32|c:\\\\windows\\\\syswow64|c:\\\\windows\\\\winsxs)"),
    1, 0)
| where IsSystemBinary=1 AND IsSystemPath=0
| table _time, host, User, Image, CommandLine, ParentImage, ParentCommandLine, CurrentDirectory
| sort - _time

process where event.type == "start"
  and process.name : ("net.exe", "cmd.exe", "powershell.exe", "whoami.exe", "ipconfig.exe", "tasklist.exe")
  and not process.executable : ("C:\\Windows\\*", "C:\\Windows\\SysWOW64\\*")

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_008_hijack_execution {
  meta:
    author = "Detection Engineering"
    description = "Detects execution flow hijacking via installer or DLL path manipulation"
    severity = "high"
    confidence = "high"
    mitre_attack = "T1574.008"
    reference = "https://attack.mitre.org/techniques/T1574/008/"

  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)