TI map URL entity to Web Session Events (ASIM Web Session schema)

Severity: medium
Time window: 14d
Group by: Id, IndicatorId, MaliciousUrl, RequestedUrl
Source: github.com/Azure/Azure-Sentinel

This rule identifies Web Sessions where the full requested URL matches a known malicious URL from Threat Intelligence sources. The rule uses the Advanced Security Information Model (ASIM) and supports any web session source compliant with ASIM.

MITRE ATT&CK coverage

Tactic	Techniques
Command & Control	`T1071` Application Layer Protocol

Rule body kusto

id: 3b4a8c72-5a2e-4f1e-b61a-9d8b2a6d7a21
name: TI map URL entity to Web Session Events (ASIM Web Session schema)
description: |
  This rule identifies Web Sessions where the full requested URL matches a known
  malicious URL from Threat Intelligence sources. The rule uses the Advanced Security
  Information Model (ASIM) and supports any web session source compliant with ASIM.
severity: Medium
queryFrequency: 1h
queryPeriod: 14d
triggerOperator: gt
triggerThreshold: 0
kind: Scheduled
tactics:
  - CommandAndControl
  - InitialAccess
relevantTechniques:
  - T1071
requiredDataConnectors:
  - connectorId: SquidProxy
    dataTypes:
      - SquidProxy_CL
  - connectorId: Zscaler
    dataTypes:
      - CommonSecurityLog
  - connectorId: ThreatIntelligence
    dataTypes:
      - ThreatIntelIndicators
  - connectorId: ThreatIntelligenceTaxii
    dataTypes:
      - ThreatIntelIndicators
  - connectorId: MicrosoftDefenderThreatIntelligence
    dataTypes:
      - ThreatIntelIndicators
query: |
  let HAS_ANY_MAX = 10000;
  let dt_lookBack = 1h;
  let ioc_lookBack = 14d;
  // Extract URL-based Threat Intelligence indicators
  let URL_TI =
    ThreatIntelIndicators
    | extend IndicatorType = replace(@"\[|\]|\""", "", tostring(split(ObservableKey, ":", 0)))
    | where IndicatorType == "url"
    | extend MaliciousUrl = tolower(ObservableValue)
    | extend TrafficLightProtocolLevel = tostring(parse_json(AdditionalFields).TLPLevel)
    | extend IndicatorId = tostring(split(Id, "--")[2])
    | where TimeGenerated >= ago(ioc_lookBack)
    | summarize LatestIndicatorTime = arg_max(TimeGenerated, *) by Id, MaliciousUrl
    | where IsActive and (ValidUntil > now() or isempty(ValidUntil));
  // Build a dynamic list of malicious URLs
  let URL_TI_list =
    toscalar(
        URL_TI
        | summarize NIoCs = dcount(MaliciousUrl),
                    Urls = make_set(MaliciousUrl)
        | project Urls = iff(NIoCs > HAS_ANY_MAX, dynamic([]), Urls)
      );
  // Match against ASIM Web Session events
  URL_TI
  | join kind=innerunique (
      _Im_WebSession(starttime=ago(dt_lookBack), url_has_any = URL_TI_list)
      | extend RequestedUrl = tolower(Url)
      | where isnotempty(RequestedUrl)
      | extend Event_TimeGenerated = TimeGenerated
    ) on $left.MaliciousUrl == $right.RequestedUrl
  | where Event_TimeGenerated < ValidUntil
  | summarize Event_TimeGenerated = arg_max(Event_TimeGenerated, *) by IndicatorId, RequestedUrl
  | extend ParsedData = parse_json(Data)
  | extend Description = tostring(ParsedData.description)
  | extend ActivityGroupNames = extract(@"ActivityGroup:(\S+)", 1, tostring(ParsedData.labels))
  | extend ThreatType = tostring(ParsedData.indicator_types[0])
  | project
      Event_TimeGenerated,
      SrcIpAddr,
      RequestedUrl,
      IndicatorId,
      ThreatType,
      Confidence,
      ValidUntil,
      Description,
      ActivityGroupNames
entityMappings:
  - entityType: IP
    fieldMappings:
      - identifier: Address
        columnName: SrcIpAddr
  - entityType: URL
    fieldMappings:
      - identifier: Url
        columnName: RequestedUrl

customDetails:
  EventTime: Event_TimeGenerated
  IoCDescription: Description
  ActivityGroupNames: ActivityGroupNames
  IndicatorId: IndicatorId
  ThreatType: ThreatType
  IoCExpirationTime: ValidUntil
  IoCConfidenceScore: Confidence

alertDetailsOverride:
  alertDisplayNameFormat: A web request from {{SrcIpAddr}} to malicious URL matched an IoC
  alertDescriptionFormat: A client with address {{SrcIpAddr}} requested the URL {{RequestedUrl}}, which is a known malicious URL associated with {{ThreatType}}. Review threat intelligence blade for further context.
version: 1.0.0

Stages and Predicates

Parameters

let HAS_ANY_MAX = 10000;
let dt_lookBack = 1h;
let ioc_lookBack = 14d;

Let binding: `URL_TI_list`

let URL_TI_list = toscalar(
      URL_TI
      | summarize NIoCs = dcount(MaliciousUrl),
                  Urls = make_set(MaliciousUrl)
      | project Urls = iff(NIoCs > HAS_ANY_MAX, dynamic([]), Urls)
    );

Derived from HAS_ANY_MAX, URL_TI.

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

Stage 1: `source`

ThreatIntelIndicators

Stage 2: `extend`

| extend IndicatorType = replace(@"\[|\]|\""", "", tostring(split(ObservableKey, ":", 0)))

Stage 3: `where`

| where IndicatorType == "url"

Stage 4: `extend` (3 consecutive steps)

| extend MaliciousUrl = tolower(ObservableValue)
| extend TrafficLightProtocolLevel = tostring(parse_json(AdditionalFields).TLPLevel)
| extend IndicatorId = tostring(split(Id, "--")[2])

Stage 5: `where`

| where TimeGenerated >= ago(ioc_lookBack)

Stage 6: `summarize`

| summarize LatestIndicatorTime = arg_max(TimeGenerated, *) by Id, MaliciousUrl

Stage 7: `where`

| where IsActive and (ValidUntil > now() or isempty(ValidUntil))

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

Stage 8: `join`

URL_TI
| join kind=innerunique (
    _Im_WebSession(starttime=ago(dt_lookBack), url_has_any = URL_TI_list)
    | extend RequestedUrl = tolower(Url)
    | where isnotempty(RequestedUrl)
    | extend Event_TimeGenerated = TimeGenerated
  ) on $left.MaliciousUrl == $right.RequestedUrl

Stage 9: `where`

| where Event_TimeGenerated < ValidUntil

Stage 10: `summarize`

| summarize Event_TimeGenerated = arg_max(Event_TimeGenerated, *) by IndicatorId, RequestedUrl

Stage 11: `extend` (4 consecutive steps)

| extend ParsedData = parse_json(Data)
| extend Description = tostring(ParsedData.description)
| extend ActivityGroupNames = extract(@"ActivityGroup:(\S+)", 1, tostring(ParsedData.labels))
| extend ThreatType = tostring(ParsedData.indicator_types[0])

Stage 12: `project`

| project
    Event_TimeGenerated,
    SrcIpAddr,
    RequestedUrl,
    IndicatorId,
    ThreatType,
    Confidence,
    ValidUntil,
    Description,
    ActivityGroupNames

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
`Event_TimeGenerated`	lt	`ValidUntil` transforms: `cased`
`IndicatorType`	eq	`url` transforms: `cased`
`RequestedUrl`	is_not_null	(no value, null check)
`ValidUntil`	is_null	(no value, null check)

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
`ActivityGroupNames`	`project`
`Confidence`	`project`
`Description`	`project`
`Event_TimeGenerated`	`project`
`IndicatorId`	`project`
`RequestedUrl`	`project`
`SrcIpAddr`	`project`
`ThreatType`	`project`
`ValidUntil`	`project`

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`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)

TI map URL entity to Web Session Events (ASIM Web Session schema)

MITRE ATT&CK coverage

Rule body kusto

Stages and Predicates

Parameters

Let binding: `URL_TI_list`

Stage 1: `source`

Stage 2: `extend`

Stage 3: `where`

Stage 4: `extend` (3 consecutive steps)

Stage 5: `where`

Stage 6: `summarize`

Stage 7: `where`

Stage 8: `join`

Stage 9: `where`

Stage 10: `summarize`

Stage 11: `extend` (4 consecutive steps)

Stage 12: `project`

Indicators

Output fields

Keyboard shortcuts

Search operators

TI map URL entity to Web Session Events (ASIM Web Session schema)

MITRE ATT&CK coverage

Rule body kusto

Stages and Predicates

Parameters

Let binding: URL_TI_list

Stage 1: source

Stage 2: extend

Stage 3: where

Stage 4: extend (3 consecutive steps)

Stage 5: where

Stage 6: summarize

Stage 7: where

Stage 8: join

Stage 9: where

Stage 10: summarize

Stage 11: extend (4 consecutive steps)

Stage 12: project

Indicators

Output fields

Let binding: `URL_TI_list`

Stage 1: `source`

Stage 2: `extend`

Stage 3: `where`

Stage 4: `extend` (3 consecutive steps)

Stage 5: `where`

Stage 6: `summarize`

Stage 7: `where`

Stage 8: `join`

Stage 9: `where`

Stage 10: `summarize`

Stage 11: `extend` (4 consecutive steps)

Stage 12: `project`