Malicious web application requests linked with Microsoft Defender for Endpoint (formerly Microsoft Defender ATP) alerts

Severity: medium
Time window: 7d
Group by: AttackerIP, HostName, ShellLocation, SiteName
Author: Microsoft Security Research
Source: github.com/Azure/Azure-Sentinel

'Takes Microsoft Defender for Endpoint (formerly Microsoft Defender ATP) alerts where web scripts are present in the evidence and correlates with requests made to those scripts in the WCSIISLog to surface new alerts for potentially malicious web request activity. The lookback for alerts is set to 1h and the lookback for W3CIISLogs is set to 7d. A sample set of popular web script extensions has been provided in scriptExtensions that should be tailored to your environment.'

MITRE ATT&CK coverage

Tactic	Techniques
Persistence	`T1505` Server Software Component

Rule body kusto

id: fbfbf530-506b-49a4-81ad-4030885a195c
name: Malicious web application requests linked with Microsoft Defender for Endpoint (formerly Microsoft Defender ATP) alerts
description: |
  'Takes Microsoft Defender for Endpoint (formerly Microsoft Defender ATP) alerts where web scripts are present in the evidence and correlates with requests made to those scripts in the WCSIISLog to surface new alerts for potentially malicious web request activity.
  The lookback for alerts is set to 1h and the lookback for W3CIISLogs is set to 7d. A sample set of popular web script extensions has been provided in scriptExtensions that should be tailored to your environment.'
severity: Medium
requiredDataConnectors:
  - connectorId: MicrosoftDefenderAdvancedThreatProtection
    dataTypes:
      - SecurityAlert
  - connectorId: AzureMonitor(IIS)
    dataTypes:
      - W3CIISLog
queryFrequency: 1h
queryPeriod: 7d
triggerOperator: gt
triggerThreshold: 0
tactics:
  - Persistence
relevantTechniques:
  - T1505
query: |
  let alertTimeWindow = 1h;
  let logTimeWindow = 7d;
  // Define script extensions that suit your web application environment - a sample are provided below
  let scriptExtensions = dynamic([".php", ".jsp", ".js", ".aspx", ".asmx", ".asax", ".cfm", ".shtml"]);
  let alertData = materialize(SecurityAlert
  | where TimeGenerated > ago(alertTimeWindow)
  | where ProviderName == "MDATP"
  // Parse and expand the alert JSON
  | extend alertData = parse_json(Entities)
  | mvexpand alertData);
  let fileData = alertData
  // Extract web script files from MDATP alerts - our malicious web scripts - candidate webshells
  | where alertData.Type =~ "file"
  | where alertData.Name has_any(scriptExtensions)
  | extend FileName = tostring(alertData.Name), Directory = tostring(alertData.Directory);
  let hostData = alertData
  // Extract server details from alerts and map to alert id
  | where alertData.Type =~ "host"
  | project HostName = tostring(alertData.HostName), DnsDomain = tostring(alertData.DnsDomain), SystemAlertId
  | distinct HostName, DnsDomain, SystemAlertId;
  // Join the files on their impacted servers
  let webshellData = fileData
  | join kind=inner (hostData) on SystemAlertId
  | project TimeGenerated, FileName, Directory, HostName, DnsDomain;
  webshellData
  | join (
  // Find requests that were made to this file on the impacted server in the W3CIISLog table
  W3CIISLog
  | where TimeGenerated > ago(logTimeWindow)
  // Restrict to accesses to script extensions
  | where csUriStem has_any(scriptExtensions)
  | extend splitUriStem = split(csUriStem, "/")
  | extend FileName = splitUriStem[-1], HostName = sComputerName
  // Summarize potential attacker activity
  | summarize count(), StartTime=min(TimeGenerated), EndTime=max(TimeGenerated), RequestUserAgents=make_set(csUserAgent), ReqestMethods=make_set(csMethod), RequestStatusCodes=make_set(scStatus), RequestCookies=make_set(csCookie), RequestReferers=make_set(csReferer), RequestQueryStrings=make_set(csUriQuery) by AttackerIP=cIP, SiteName=sSiteName, ShellLocation=csUriStem, tostring(FileName), HostName
  ) on FileName, HostName
  | project StartTime, EndTime, AttackerIP, RequestUserAgents, Computer = HostName, SiteName, ShellLocation, ReqestMethods, RequestStatusCodes, RequestCookies, RequestReferers, RequestQueryStrings, RequestCount = count_
  | extend HostName = tostring(split(Computer, ".")[0]), DomainIndex = toint(indexof(Computer, '.'))
  | extend HostNameDomain = iff(DomainIndex != -1, substring(Computer, DomainIndex + 1), Computer)
entityMappings:
  - entityType: Host
    fieldMappings:
      - identifier: FullName
        columnName: Computer
      - identifier: HostName
        columnName: HostName
      - identifier: DnsDomain
        columnName: HostNameDomain
  - entityType: IP
    fieldMappings:
      - identifier: Address
        columnName: AttackerIP
version: 1.0.4
kind: Scheduled
metadata:
    source:
        kind: Scheduled
    author:
        name: Microsoft Security Research
    support:
        tier: Community
    categories:
        domains: [ "Security - Others" ]

Stages and Predicates

Parameters

let alertTimeWindow = 1h;
let logTimeWindow = 7d;
let scriptExtensions = dynamic([".php", ".jsp", ".js", ".aspx", ".asmx", ".asax", ".cfm", ".shtml"]);

Let binding: `hostData`

let hostData = alertData
| where alertData.Type =~ "host"
| project HostName = tostring(alertData.HostName), DnsDomain = tostring(alertData.DnsDomain), SystemAlertId
| distinct HostName, DnsDomain, SystemAlertId;

Derived from alertData.

The stages below define let webshellData (the rule's main pipeline source).

Stage 1: `source`

SecurityAlert

Stage 2: `where`

| where TimeGenerated > ago(alertTimeWindow)

Stage 3: `where`

| where ProviderName == "MDATP"

Stage 4: `extend`

| extend alertData = parse_json(Entities)

Stage 5: `mv-expand`

| mvexpand alertData

Stage 6: `where`

| where alertData.Type =~ "file"

Stage 7: `where`

| where alertData.Name has_any(scriptExtensions)

Stage 8: `extend`

| extend FileName = tostring(alertData.Name), Directory = tostring(alertData.Directory)

Stage 9: `join`

| join kind=inner (hostData) on SystemAlertId

Stage 10: `project`

| project TimeGenerated, FileName, Directory, HostName, DnsDomain

The stages below run on webshellData (the outer pipeline).

Stage 11: `join`

webshellData
| join (
W3CIISLog
| where TimeGenerated > ago(logTimeWindow)
| where csUriStem has_any(scriptExtensions)
| extend splitUriStem = split(csUriStem, "/")
| extend FileName = splitUriStem[-1], HostName = sComputerName
| summarize count(), StartTime=min(TimeGenerated), EndTime=max(TimeGenerated), RequestUserAgents=make_set(csUserAgent), ReqestMethods=make_set(csMethod), RequestStatusCodes=make_set(scStatus), RequestCookies=make_set(csCookie), RequestReferers=make_set(csReferer), RequestQueryStrings=make_set(csUriQuery) by AttackerIP=cIP, SiteName=sSiteName, ShellLocation=csUriStem, tostring(FileName), HostName
) on FileName, HostName

Stage 12: `project`

| project StartTime, EndTime, AttackerIP, RequestUserAgents, Computer = HostName, SiteName, ShellLocation, ReqestMethods, RequestStatusCodes, RequestCookies, RequestReferers, RequestQueryStrings, RequestCount = count_

Stage 13: `extend`

| extend HostName = tostring(split(Computer, ".")[0]), DomainIndex = toint(indexof(Computer, '.'))

Stage 14: `extend`

| extend HostNameDomain = iff(DomainIndex != -1, substring(Computer, DomainIndex + 1), Computer)

HostNameDomain =

ifDomainIndex != -1substring(Computer, (DomainIndex + 1))

elseComputer

Stage 15: `summarize`

summarize by AttackerIP, SiteName, ShellLocation, HostName

Indicators

Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.

Field	Kind	Values
`Name`	match	`.asax` `.asmx` `.aspx` `.cfm` `.js` `.jsp` `.php` `.shtml`
`ProviderName`	eq	`MDATP` transforms: `cased` corpus 13 (kusto 13)
`Type`	eq	`file` corpus 2 (kusto 2) `host` corpus 2 (kusto 2)
`csUriStem`	match	`.asax` `.asmx` `.aspx` `.cfm` `.js` `.jsp` `.php` `.shtml`

Output fields

Fields the rule emits when it matches. Chronicle authors list these in the outcome block; they appear on the detection and $risk_score drives alerting. Sentinel / Defender XDR rules build them up through project / summarize / extend stages. Sentinel maps these into alert fields via entityMappings and customDetails; Defender XDR custom detections surface them as alert fields directly.

Field	Source
`AttackerIP`	`summarize`
`HostName`	`summarize`
`ShellLocation`	`summarize`
`SiteName`	`summarize`

`j` / `k`	Scroll down / up
`d` / `u`	Half-page down / up
`gg` / `G`	Top / bottom
`h` / `l`	History back / forward
`f`	Follow link (`Shift` = new tab)
`/`	Focus search
`?`	Toggle this help
`↑` / `↓`	Navigate search results
`Enter`	Open highlighted result
`Esc`	Close results / dialog

`type:`	`events` / `rules` / `providers`
`vendor:`	`sigma` / `elastic` / `splunk` / `kusto` / `chronicle` (vendor name alone also works: `sigma:`, `kql:`, `secops:`…)
`tactic:`	TA-id, slug, or name: `credential_access`, `TA0006`
`technique:`	technique or sub-technique ID: `T1003`, `T1003.001` (alias `tech:`)
`severity:`	`critical` / `high` / `medium` / `low` / `informational` (alias `sev:`)
`risk_score`	Numeric comparison on the Elastic risk score (0 to 100): `risk_score>50`, `risk_score<=20`, `risk_score=99` (alias `risk`; Elastic rules only)
`stages:`	Rules with exactly N pipeline stages
`correlation:`	`single_event` / `sequence` / `alternatives` / `alternatives_cross_log` / `all_required` / `correlated`
`with:`	Co-occurrence event-id; stacks (`with:4624 with:4769`) to require all, while a comma list in one occurrence (`with:4624,4769`) is an either-or group. Implies multi-event
`like:`	Structural neighbors of a rule slug (equivalents + subsumption stricter / broader): `like:comsvcs_lsass_memory_dump-splunk-sysmon`
`groupby:`	Entity-grouping substring match against `group_by_keys`: `groupby:user`, `groupby:host`
`uses:`	Rules whose predicate tree touches the field (any kind, any value): `uses:CommandLine`
`excludes:`	Rules with top-level `not()` clauses on the field (FP whitelists): `excludes:ParentImage`
`field:` / `value:`	Predicate search; narrows rule cards to those with a matching leaf and drives the indicator tier. Unquoted = substring, wildcards allowed (`value:mimikatz`)
`indicator:`	Shorthand for `field:F value:V`: `indicator:Image=*\powershell.exe`
`kind:`	Filter by predicate kind. Narrows rule cards to those carrying a matching predicate leaf (`vendor:elastic kind:cidr_match`) and drives the indicator tier: `contains` / `starts_with` / `ends_with` / `regex` / `cidr` / `eq` / `in` … (operator aliases `op:`/`match:`)
`has:` / `no:`	`sample`, `field`, `notes`, `refs`, `trace`, `thirdparty`, `rule`, `pattern`, `timewindow`, `threshold`, `newterms`, `sigma`/`elastic`/`splunk`/`kusto`/`chronicle`
`-op:val`	Exclude matches; works on most operators but not `type:`/`like:`/`has:`/`no:` (use `no:<flag>` to exclude a rule flag): `tactic:execution -vendor:splunk`. Standalone `-kind:`/`-field:`/`-value:` drop every rule carrying a matching predicate leaf (`type:rules -kind:is_null`)
`field:"…"` / `value:"…"`	Quoted value = anchored exact match (also allows spaces): `value:"net user"`
`a,b`	Comma = OR inside one operator (`vendor:sigma,elastic`, `severity:high,critical`); repeating a facet merges the same way. `field:`/`value:` never split (literal commas)
`vendors:` / `stage:`	Singular and plural spellings fold to the canonical operator and value: `tactics:` = `tactic:`, `type:event` = `type:events`, `correlation:sequences` = `correlation:sequence`, `has:thresholds` = `has:threshold`
`"quoted phrase"`	Exact-match a multi-word phrase (free text)

Malicious web application requests linked with Microsoft Defender for Endpoint (formerly Microsoft Defender ATP) alerts

MITRE ATT&CK coverage

Rule body kusto

Stages and Predicates

Parameters

Let binding: `hostData`

Stage 1: `source`

Stage 2: `where`

Stage 3: `where`

Stage 4: `extend`

Stage 5: `mv-expand`

Stage 6: `where`

Stage 7: `where`

Stage 8: `extend`

Stage 9: `join`

Stage 10: `project`

Stage 11: `join`

Stage 12: `project`

Stage 13: `extend`

Stage 14: `extend`

Stage 15: `summarize`

Indicators

Output fields

Keyboard shortcuts

Search operators

Malicious web application requests linked with Microsoft Defender for Endpoint (formerly Microsoft Defender ATP) alerts

MITRE ATT&CK coverage

Rule body kusto

Stages and Predicates

Parameters

Let binding: hostData

Stage 1: source

Stage 2: where

Stage 3: where

Stage 4: extend

Stage 5: mv-expand

Stage 6: where

Stage 7: where

Stage 8: extend

Stage 9: join

Stage 10: project

Stage 11: join

Stage 12: project

Stage 13: extend

Stage 14: extend

Stage 15: summarize

Indicators

Output fields

Let binding: `hostData`

Stage 1: `source`

Stage 2: `where`

Stage 3: `where`

Stage 4: `extend`

Stage 5: `mv-expand`

Stage 6: `where`

Stage 7: `where`

Stage 8: `extend`

Stage 9: `join`

Stage 10: `project`

Stage 11: `join`

Stage 12: `project`

Stage 13: `extend`

Stage 14: `extend`

Stage 15: `summarize`