Excessive number of HTTP authentication failures from a source (ASIM Web Session schema)

Severity: low
Time window: 1d
Group by: SrcIpAddr, UrlHost
Author: Yaron
Source: github.com/Azure/Azure-Sentinel

This rule identifies a source that repeatedly fails to authenticate to a web service (HTTP response code 403). This may indicate a brute force or credential stuffing attack. This rule uses the Advanced Security Information Model (ASIM) and supports any web session source that complies with ASIM.

MITRE ATT&CK coverage

Tactic	Techniques
Persistence	`T1556` Modify Authentication Process
Credential Access	`T1110` Brute Force, `T1556` Modify Authentication Process

Rule body kusto

id: a1bddaf8-982b-4089-ba9e-6590dfcf80ea
name: Excessive number of HTTP authentication failures from a source (ASIM Web Session schema)
description: |
    This rule identifies a source that repeatedly fails to authenticate to a web service (HTTP response code 403). This may indicate a [brute force](https://en.wikipedia.org/wiki/Brute-force_attack) or [credential stuffing](https://en.wikipedia.org/wiki/Credential_stuffing) attack.
    This rule uses the [Advanced Security Information Model (ASIM)](https://aka.ms/AboutASIM) and supports any web session source that complies with ASIM.
severity: Low
requiredDataConnectors:
  - connectorId: SquidProxy
    dataTypes:
      - SquidProxy_CL
  - connectorId: Zscaler
    dataTypes:
      - CommonSecurityLog
queryFrequency: 1d
queryPeriod: 1d
triggerOperator: gt
triggerThreshold: 0
tactics:
    - Persistence
    - CredentialAccess
relevantTechniques:
    - T1110
    - T1556
tags:
    - ParentAlert: https://github.com/Azure/Azure-Sentinel/blob/master/Detections/CommonSecurityLog/Wazuh-Large%20Number%20of%20Web%20errors%20from%20an%20IP.yaml
      ParentVersion: 1.1.0
    - Schema: ASIMWebSession
      SchemaVersion: 0.2.1
query: |
    let error403_count_threshold=200;
    _Im_WebSession(eventresultdetails_in=dynamic(["403"]))
    | extend ParsedUrl=parse_url(Url)
    | extend UrlHost=tostring(ParsedUrl["Host"]), UrlSchema=tostring(ParsedUrl["Schema"])
    | summarize StartTime = min(TimeGenerated), EndTime = max(TimeGenerated), NumberOfErrors = count(), Urls=makeset(Url) by UrlHost, SrcIpAddr
    | where NumberOfErrors > error403_count_threshold
    | sort by NumberOfErrors desc
    | extend Url=tostring(Urls[0])
entityMappings:
    - entityType: URL
      fieldMappings:
          - identifier: Url
            columnName: Url
    - entityType: IP
      fieldMappings:
          - identifier: Address
            columnName: SrcIpAddr
customDetails:
  NumberOfErrors: NumberOfErrors
alertDetailsOverride:
    alertDisplayNameFormat: Excessive number of HTTP authentication failures from {{SrcIpAddr}
    alertDescriptionFormat: A client with address {{SrcIpAddr}} generated a large number of failed authentication HTTP requests. This may indicate a [brute force](https://en.wikipedia.org/wiki/Brute-force_attack) or [credential stuffing](https://en.wikipedia.org/wiki/Credential_stuffing) attack.
version: 1.0.6
kind: Scheduled
metadata:
    source:
        kind: Community
    author:
        name: Yaron
    support:
        tier: Community
    categories:
        domains: [ "Security - Others" ]

Stages and Predicates

Parameters

let error403_count_threshold = 200;

Stage 1: `source`

_Im_WebSession(eventresultdetails_in=dynamic(["403"]))

Stage 2: `extend`

| extend ParsedUrl=parse_url(Url)

Stage 3: `extend`

| extend UrlHost=tostring(ParsedUrl["Host"]), UrlSchema=tostring(ParsedUrl["Schema"])

Stage 4: `summarize`

| summarize StartTime = min(TimeGenerated), EndTime = max(TimeGenerated), NumberOfErrors = count(), Urls=makeset(Url) by UrlHost, SrcIpAddr

Threshold: gt 200

Stage 5: `where`

| where NumberOfErrors > error403_count_threshold

Stage 6: `sort`

| sort by NumberOfErrors desc

Stage 7: `extend`

| extend Url=tostring(Urls[0])

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
`NumberOfErrors`	gt	`200` transforms: `cased`

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
`EndTime`	`summarize`
`NumberOfErrors`	`summarize`
`SrcIpAddr`	`summarize`
`StartTime`	`summarize`
`UrlHost`	`summarize`
`Urls`	`summarize`
`Url`	`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)

Excessive number of HTTP authentication failures from a source (ASIM Web Session schema)

MITRE ATT&CK coverage

Rule body kusto

Stages and Predicates

Parameters

Stage 1: `source`

Stage 2: `extend`

Stage 3: `extend`

Stage 4: `summarize`

Stage 5: `where`

Stage 6: `sort`

Stage 7: `extend`

Indicators

Output fields

Keyboard shortcuts

Search operators

Excessive number of HTTP authentication failures from a source (ASIM Web Session schema)

MITRE ATT&CK coverage

Rule body kusto

Stages and Predicates

Parameters

Stage 1: source

Stage 2: extend

Stage 3: extend

Stage 4: summarize

Stage 5: where

Stage 6: sort

Stage 7: extend

Indicators

Output fields

Stage 1: `source`

Stage 2: `extend`

Stage 3: `extend`

Stage 4: `summarize`

Stage 5: `where`

Stage 6: `sort`

Stage 7: `extend`