Excessive number of failed connections from a single source (ASIM Network Session schema)

Status: available
Severity: medium
Time window: 5m
Group by: SrcIpAddr
Source: github.com/Azure/Azure-Sentinel

This rule identifies a single source that generates an excessive amount of failed connections. Modify the threshold to change the sensitivity of the rule: the higher the threshold, the less sensitive is the rule and less incidents will be generated. This analytic rule uses ASIM and supports any built-in or custom source that supports the ASIM NetworkSession schema

MITRE ATT&CK coverage

Tactic	Techniques
Impact	`T1499` Endpoint Denial of Service

Event coverage

Provider	Event	Title
Sysmon	Event ID 3	Network connection
Security-Auditing	Event ID 5152	The Windows Filtering Platform blocked a packet.
Security-Auditing	Event ID 5154	The Windows Filtering Platform has permitted an application or service to listen on a port for incoming connections.
Security-Auditing	Event ID 5155	The Windows Filtering Platform has blocked an application or service from listening on a port for incoming connections.
Security-Auditing	Event ID 5156	The Windows Filtering Platform has permitted a connection.
Security-Auditing	Event ID 5157	The Windows Filtering Platform has blocked a connection.
Security-Auditing	Event ID 5158	The Windows Filtering Platform has permitted a bind to a local port.
Security-Auditing	Event ID 5159	The Windows Filtering Platform has blocked a bind to a local port.

Rule body kusto

id: 4902eddb-34f7-44a8-ac94-8486366e9494
name: Excessive number of failed connections from a single source (ASIM Network Session schema)
description: |
  'This rule identifies a single source that generates an excessive amount of failed connections. Modify the threshold to change the sensitivity of the rule: the higher the threshold, the less sensitive is the rule and less incidents will be generated.
   This analytic rule uses [ASIM](https://aka.ms/AboutASIM) and supports any built-in or custom source that supports the ASIM NetworkSession schema'
severity: Medium
status: Available
tags:
  - ParentAlert: https://github.com/Azure/Azure-Sentinel/tree/master/Solutions/Sophos%20XG%20Firewall/Analytic%20Rules/ExcessiveAmountofDeniedConnectionsfromASingleSource.yaml
    version: 1.0.0
  - Schema: ASimNetworkSessions
    SchemaVersion: 0.2.4
requiredDataConnectors:
  - connectorId: AWSS3
    dataTypes:
      - AWSVPCFlow
  - connectorId: MicrosoftThreatProtection
    dataTypes:
      - DeviceNetworkEvents
  - connectorId: SecurityEvents
    dataTypes:
      - SecurityEvent
  - connectorId: WindowsSecurityEvents
    dataTypes:
      - SecurityEvent
  - connectorId: WindowsForwardedEvents
    dataTypes:
      - WindowsEvent
  - connectorId: Zscaler
    dataTypes:
      - CommonSecurityLog
  - connectorId: MicrosoftSysmonForLinux
    dataTypes:
      - Syslog
  - connectorId: PaloAltoNetworks
    dataTypes:
      - CommonSecurityLog
  - connectorId: AzureMonitor(VMInsights)
    dataTypes:
      - VMConnection
  - connectorId: AzureFirewall
    dataTypes:
      - AzureDiagnostics
  - connectorId: AzureNSG
    dataTypes:
      - AzureDiagnostics
  - connectorId: CiscoASA
    dataTypes:
      - CommonSecurityLog
  - connectorId: CiscoAsaAma
    dataTypes:
      - CommonSecurityLog
  - connectorId: Corelight
    dataTypes:
      - Corelight_CL
  - connectorId: AIVectraStream
    dataTypes:
      - VectraStream
  - connectorId: CheckPoint
    dataTypes:
      - CommonSecurityLog
  - connectorId: Fortinet
    dataTypes:
      - CommonSecurityLog
  - connectorId: CiscoMeraki
    dataTypes:
      - Syslog
      - CiscoMerakiNativePoller

queryFrequency: 1h
queryPeriod: 1h
triggerOperator: gt
triggerThreshold: 0
tactics:
  - Impact
relevantTechniques:
  - T1499
query: |
  let threshold = 5000;
  _Im_NetworkSession(eventresult='Failure')
  | summarize Count=count() by SrcIpAddr, bin(TimeGenerated,5m)
  | where Count > threshold
  | extend timestamp = TimeGenerated, threshold
entityMappings:
  - entityType: IP
    fieldMappings:
      - identifier: Address
        columnName: SrcIpAddr
customDetails:
  NumberOfDenies: Count

alertDetailsOverride:
  alertDisplayNameFormat: Excessive number of failed connections from {{SrcIpAddr}}
  alertDescriptionFormat: 'The client at address {{SrcIpAddr}} generated more than {{threshold}} failures over a 5 minutes time window, which may indicate malicious activity.'
version: 1.2.7
kind: Scheduled

Stages and Predicates

Parameters

let threshold = 5000;

Stage 1: `source`

_Im_NetworkSession(eventresult='Failure')

Stage 2: `summarize`

| summarize Count=count() by SrcIpAddr, bin(TimeGenerated,5m)

Threshold: gt 5000

Stage 3: `where`

| where Count > threshold

Stage 4: `extend`

| extend timestamp = TimeGenerated, threshold

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
`Count`	gt	`5000` transforms: `cased` corpus 3 (kusto 3)

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
`Count`	`summarize`
`SrcIpAddr`	`summarize`
`threshold`	`extend`
`timestamp`	`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 failed connections from a single source (ASIM Network Session schema)

MITRE ATT&CK coverage

Event coverage

Rule body kusto

Stages and Predicates

Parameters

Stage 1: `source`

Stage 2: `summarize`

Stage 3: `where`

Stage 4: `extend`

Indicators

Output fields

Keyboard shortcuts

Search operators

Excessive number of failed connections from a single source (ASIM Network Session schema)

MITRE ATT&CK coverage

Event coverage

Rule body kusto

Stages and Predicates

Parameters

Stage 1: source

Stage 2: summarize

Stage 3: where

Stage 4: extend

Indicators

Output fields

Stage 1: `source`

Stage 2: `summarize`

Stage 3: `where`

Stage 4: `extend`