GSA - Detect Abnormal Deny Rate for Source to Destination IP

Status: available
Severity: medium
Time window: 7d
Group by: DestinationIp, SourceIp
Source: github.com/Azure/Azure-Sentinel

Identifies abnormal deny rate for specific source IP to destination IP based on the normal average and standard deviation learned during a configured period. This can indicate potential exfiltration, initial access, or C2, where an attacker tries to exploit the same vulnerability on machines in the organization but is being blocked by firewall rules. Configurable Parameters: - minimumOfStdsThreshold: The number of stds to use in the threshold calculation. Default is set to 3. - learningPeriodTime: Learning period for threshold calculation in days. Default is set to 5. - binTime: Learning buckets time in hours. Default is set to 1 hour. - minimumThreshold: Minimum threshold for alert. Default is set to 5. - minimumBucketThreshold: Minimum learning buckets threshold for alert. Default is set to 5.

MITRE ATT&CK coverage

Tactic	Techniques
Command & Control	`T1571` Non-Standard Port

Rule body kusto

id: e3b6a9e7-4c3a-45e6-8baf-1d3bfa8e0c2b
name: GSA - Detect Abnormal Deny Rate for Source to Destination IP
description: |
  Identifies abnormal deny rate for specific source IP to destination IP based on the normal average and standard deviation learned during a configured period. This can indicate potential exfiltration, initial access, or C2, where an attacker tries to exploit the same vulnerability on machines in the organization but is being blocked by firewall rules.
  
  Configurable Parameters:
      - minimumOfStdsThreshold: The number of stds to use in the threshold calculation. Default is set to 3.
      - learningPeriodTime: Learning period for threshold calculation in days. Default is set to 5.
      - binTime: Learning buckets time in hours. Default is set to 1 hour.
      - minimumThreshold: Minimum threshold for alert. Default is set to 5.
      - minimumBucketThreshold: Minimum learning buckets threshold for alert. Default is set to 5.
severity: Medium
status: Available
requiredDataConnectors:
  - connectorId: AzureActiveDirectory
    dataTypes:
      - NetworkAccessTrafficLogs
queryFrequency: 1h
queryPeriod: 7d
triggerOperator: gt
triggerThreshold: 1
tactics:
  - InitialAccess
  - Exfiltration
  - CommandAndControl
relevantTechniques:
  - T1571
query: |
  let NumOfStdsThreshold = 3;
  let LearningPeriod = 5d;
  let BinTime = 1h;
  let MinThreshold = 5.0;
  let MinLearningBuckets = 5;
  let TrafficLogs = NetworkAccessTraffic
    | where Action == "Denied"
    | where isnotempty(DestinationIp) and isnotempty(SourceIp);
  let LearningSrcIpDenyRate = TrafficLogs
    | where TimeGenerated between (ago(LearningPeriod + 1d) .. ago(1d))
    | summarize count_ = count() by SourceIp, bin(TimeGenerated, BinTime), DestinationIp
    | summarize LearningTimeSrcIpDenyRateAvg = avg(count_), LearningTimeSrcIpDenyRateStd = stdev(count_), LearningTimeBuckets = count() by SourceIp, DestinationIp
    | where LearningTimeBuckets > MinLearningBuckets;
  let AlertTimeSrcIpDenyRate = TrafficLogs
    | where TimeGenerated between (ago(1h) .. now())
    | summarize AlertTimeSrcIpDenyRateCount = count() by SourceIp, DestinationIp;
  AlertTimeSrcIpDenyRate
    | join kind=leftouter (LearningSrcIpDenyRate) on SourceIp, DestinationIp
    | extend LearningThreshold = max_of(LearningTimeSrcIpDenyRateAvg + NumOfStdsThreshold * LearningTimeSrcIpDenyRateStd, MinThreshold)
    | where AlertTimeSrcIpDenyRateCount > LearningThreshold
    | project SourceIp, DestinationIp, AlertTimeSrcIpDenyRateCount, LearningThreshold
entityMappings:
  - entityType: IP
    fieldMappings:
      - identifier: Address
        columnName: SourceIp
  - entityType: URL
    fieldMappings:
      - identifier: Url
        columnName: DestinationIp
version: 1.0.4
kind: Scheduled

Stages and Predicates

Parameters

let NumOfStdsThreshold = 3;
let LearningPeriod = 5d;
let BinTime = 1h;
let MinThreshold = 5.0;
let MinLearningBuckets = 5;

Let binding: `LearningSrcIpDenyRate`

let LearningSrcIpDenyRate = TrafficLogs
  | where TimeGenerated between (ago(LearningPeriod + 1d) .. ago(1d))
  | summarize count_ = count() by SourceIp, bin(TimeGenerated, BinTime), DestinationIp
  | summarize LearningTimeSrcIpDenyRateAvg = avg(count_), LearningTimeSrcIpDenyRateStd = stdev(count_), LearningTimeBuckets = count() by SourceIp, DestinationIp
  | where LearningTimeBuckets > MinLearningBuckets;

Derived from LearningPeriod, BinTime, MinLearningBuckets, TrafficLogs.

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

Stage 1: `source`

NetworkAccessTraffic

Stage 2: `where`

| where Action == "Denied"

Stage 3: `where`

| where isnotempty(DestinationIp) and isnotempty(SourceIp)

Stage 4: `where`

| where TimeGenerated between (ago(1h) .. now())

Stage 5: `summarize`

| summarize AlertTimeSrcIpDenyRateCount = count() by SourceIp, DestinationIp

Threshold: gt LearningThreshold

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

Stage 6: `join`

AlertTimeSrcIpDenyRate
| join kind=leftouter (LearningSrcIpDenyRate) on SourceIp, DestinationIp

Stage 7: `extend`

| extend LearningThreshold = max_of(LearningTimeSrcIpDenyRateAvg + NumOfStdsThreshold * LearningTimeSrcIpDenyRateStd, MinThreshold)

Stage 8: `where`

| where AlertTimeSrcIpDenyRateCount > LearningThreshold

Stage 9: `project`

| project SourceIp, DestinationIp, AlertTimeSrcIpDenyRateCount, LearningThreshold

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
`Action`	eq	`Denied` transforms: `cased`
`AlertTimeSrcIpDenyRateCount`	gt	`LearningThreshold` transforms: `cased`
`DestinationIp`	is_not_null	(no value, null check)
`LearningTimeBuckets`	gt	`5` transforms: `cased`
`SourceIp`	is_not_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
`AlertTimeSrcIpDenyRateCount`	`project`
`DestinationIp`	`project`
`LearningThreshold`	`project`
`SourceIp`	`project`

`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)

GSA - Detect Abnormal Deny Rate for Source to Destination IP

MITRE ATT&CK coverage

Rule body kusto

Stages and Predicates

Parameters

Let binding: `LearningSrcIpDenyRate`

Stage 1: `source`

Stage 2: `where`

Stage 3: `where`

Stage 4: `where`

Stage 5: `summarize`

Stage 6: `join`

Stage 7: `extend`

Stage 8: `where`

Stage 9: `project`

Indicators

Output fields

Keyboard shortcuts

Search operators

GSA - Detect Abnormal Deny Rate for Source to Destination IP

MITRE ATT&CK coverage

Rule body kusto

Stages and Predicates

Parameters

Let binding: LearningSrcIpDenyRate

Stage 1: source

Stage 2: where

Stage 3: where

Stage 4: where

Stage 5: summarize

Stage 6: join

Stage 7: extend

Stage 8: where

Stage 9: project

Indicators

Output fields

Let binding: `LearningSrcIpDenyRate`

Stage 1: `source`

Stage 2: `where`

Stage 3: `where`

Stage 4: `where`

Stage 5: `summarize`

Stage 6: `join`

Stage 7: `extend`

Stage 8: `where`

Stage 9: `project`