A host is potentially running PowerShell to send HTTP(S) requests (ASIM Web Session schema)

Severity: medium
Time window: 15m
Author: Yaron
Source: github.com/Azure/Azure-Sentinel

'This rule identifies a web request with a user agent header known to belong PowerShell. <br>You can add custom Powershell indicating User-Agent headers using a watchlist, for more information refer to the UnusualUserAgents Watchlist.<br><br> This analytic rule uses ASIM and supports any built-in or custom source that supports the ASIM WebSession schema (ASIM WebSession Schema)'

MITRE ATT&CK coverage

Tactic	Techniques
Execution	`T1059.001` Command and Scripting Interpreter: PowerShell
Stealth	`T1140` Deobfuscate/Decode Files or Information
Command & Control	`T1132` Data Encoding

Rule body kusto

id: 42436753-9944-4d70-801c-daaa4d19ddd2
name: A host is potentially running PowerShell to send HTTP(S) requests (ASIM Web Session schema)
description: |
  'This rule identifies a web request with a user agent header known to belong PowerShell. <br>You can add custom Powershell indicating User-Agent headers using a watchlist, for more information refer to the [UnusualUserAgents Watchlist](https://aka.ms/ASimUnusualUserAgentsWatchlist).<br><br>
   This analytic rule uses [ASIM](https://aka.ms/AboutASIM) and supports any built-in or custom source that supports the ASIM WebSession schema (ASIM WebSession Schema)'
severity: Medium
tags:
  - ParentAlert: https://github.com/Azure/Azure-Sentinel/blob/master/Detections/CiscoUmbrella/CiscoUmbrellaPowershellUserAgentDetected.yaml
    version: 1.0.0
  - Schema: ASimWebSession
    SchemaVersion: 0.2.1
requiredDataConnectors:
  - connectorId: SquidProxy
    dataTypes:
      - SquidProxy_CL
  - connectorId: Zscaler
    dataTypes:
      - CommonSecurityLog

queryFrequency: 15m
queryPeriod: 15m
triggerOperator: gt
triggerThreshold: 0
tactics:
  - CommandAndControl
  - DefenseEvasion
  - Execution
relevantTechniques:
  - T1132
  - T1140
  - T1059.001
query: |
    let threatCategory="Powershell";
    let knownUserAgentsIndicators = materialize(externaldata(UserAgent:string, Category:string)
        [ @"https://raw.githubusercontent.com/Azure/Azure-Sentinel/master/Sample%20Data/Feeds/UnusualUserAgents.csv"]
            with(format="csv", ignoreFirstRecord=True));
    let knownUserAgents=toscalar(knownUserAgentsIndicators | where Category==threatCategory | where isnotempty(UserAgent) | summarize make_list(UserAgent));
    let customUserAgents=toscalar(_GetWatchlist("UnusualUserAgents") | where SearchKey==threatCategory | extend UserAgent=column_ifexists("UserAgent","") | where isnotempty(UserAgent) | summarize make_list(UserAgent));
    let fullUAList = array_concat(knownUserAgents,customUserAgents);
    _Im_WebSession(httpuseragent_has_any=fullUAList)
    | project SrcIpAddr, Url, TimeGenerated, HttpUserAgent, SrcUsername
    | extend AccountName = tostring(split(SrcUsername, "@")[0]), AccountUPNSuffix = tostring(split(SrcUsername, "@")[1])
entityMappings:
  - entityType: URL
    fieldMappings:
      - identifier: Url
        columnName: Url
  - entityType: IP
    fieldMappings:
      - identifier: Address
        columnName: SrcIpAddr
  - entityType: Account
    fieldMappings:
      - identifier: FullName
        columnName: SrcUsername
      - identifier: Name
        columnName: AccountName
      - identifier: UPNSuffix
        columnName: AccountUPNSuffix

alertDetailsOverride:
  alertDisplayNameFormat: 'Host {{SrcIpAddr}} is potentially running PowerShell'
  alertDescriptionFormat: 'The host at address {{SrcIpAddr}} sent an HTTP request to the URL {{Url}} with the HTTP user agent header {{HttpUserAgent}}. This user agent is known to be used by PowerShell and indicates suspicious activity on the host.'
customDetails:
  UserAgent: HttpUserAgent

eventGroupingSettings:
  aggregationKind: AlertPerResult
version: 1.1.5
kind: Scheduled
metadata:
    source:
        kind: Community
    author:
        name: Yaron
    support:
        tier: Community
    categories:
        domains: [ "Security - Threat Protection" ]

Stages and Predicates

Parameters

let threatCategory = "Powershell";
let fullUAList = array_concat(knownUserAgents,customUserAgents);

Let binding: `knownUserAgentsIndicators`

let knownUserAgentsIndicators = materialize(externaldata(UserAgent:string, Category:string)
    [ @"https://raw.githubusercontent.com/Azure/Azure-Sentinel/master/Sample%20Data/Feeds/UnusualUserAgents.csv"]
        with(format="csv", ignoreFirstRecord=True));

Let binding: `knownUserAgents`

let knownUserAgents = toscalar(knownUserAgentsIndicators | where Category==threatCategory | where isnotempty(UserAgent) | summarize make_list(UserAgent));

Derived from threatCategory, knownUserAgentsIndicators.

Let binding: `customUserAgents`

let customUserAgents = toscalar(_GetWatchlist("UnusualUserAgents") | where SearchKey==threatCategory | extend UserAgent=column_ifexists("UserAgent","") | where isnotempty(UserAgent) | summarize make_list(UserAgent));

Derived from threatCategory.

Stage 1: `source`

_Im_WebSession(httpuseragent_has_any=fullUAList)

Stage 2: `project`

| project SrcIpAddr, Url, TimeGenerated, HttpUserAgent, SrcUsername

Stage 3: `extend`

| extend AccountName = tostring(split(SrcUsername, "@")[0]), AccountUPNSuffix = tostring(split(SrcUsername, "@")[1])

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
`HttpUserAgent`	`project`
`SrcIpAddr`	`project`
`SrcUsername`	`project`
`TimeGenerated`	`project`
`Url`	`project`
`AccountName`	`extend`
`AccountUPNSuffix`	`extend`

`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)

A host is potentially running PowerShell to send HTTP(S) requests (ASIM Web Session schema)

MITRE ATT&CK coverage

Rule body kusto

Stages and Predicates

Parameters

Let binding: `knownUserAgentsIndicators`

Let binding: `knownUserAgents`

Let binding: `customUserAgents`

Stage 1: `source`

Stage 2: `project`

Stage 3: `extend`

Output fields

Keyboard shortcuts

Search operators

A host is potentially running PowerShell to send HTTP(S) requests (ASIM Web Session schema)

MITRE ATT&CK coverage

Rule body kusto

Stages and Predicates

Parameters

Let binding: knownUserAgentsIndicators

Let binding: knownUserAgents

Let binding: customUserAgents

Stage 1: source

Stage 2: project

Stage 3: extend

Output fields

Let binding: `knownUserAgentsIndicators`

Let binding: `knownUserAgents`

Let binding: `customUserAgents`

Stage 1: `source`

Stage 2: `project`

Stage 3: `extend`