Azure WAF matching for Log4j vuln(CVE-2021-44228)

Status: available
Severity: high
Time window: 6h
Source: github.com/Azure/Azure-Sentinel

'This query will alert on a positive pattern match by Azure WAF for CVE-2021-44228 log4j vulnerability exploitation attempt. If possible, it then decodes the malicious command for further analysis. Reference: https://www.microsoft.com/security/blog/2021/12/11/guidance-for-preventing-detecting-and-hunting-for-cve-2021-44228-log4j-2-exploitation/'

MITRE ATT&CK coverage

Tactic	Techniques
Initial Access	`T1190` Exploit Public-Facing Application

Rule body kusto

id: 2de8abd6-a613-450e-95ed-08e503369fb3
name: Azure WAF matching for Log4j vuln(CVE-2021-44228)
description: |
  'This query will alert on a positive pattern match by Azure WAF for CVE-2021-44228 log4j vulnerability exploitation attempt. If possible, it then decodes the malicious command for further analysis.
   Reference: https://www.microsoft.com/security/blog/2021/12/11/guidance-for-preventing-detecting-and-hunting-for-cve-2021-44228-log4j-2-exploitation/'
severity: High
status: Available
requiredDataConnectors:
  - connectorId: WAF
    dataTypes:
      - AzureDiagnostics
queryFrequency: 6h
queryPeriod: 6h
triggerOperator: gt
triggerThreshold: 0
tactics:
  - InitialAccess
relevantTechniques:
  - T1190
tags:
  - CVE-2021-44228
  - log4j 
  - log4shell
query: |
  let log4jioc = dynamic(["jndi","ldap","${::"]);
  AzureDiagnostics
  | where ResourceProvider == "MICROSOFT.NETWORK" and Category in ("ApplicationGatewayFirewallLog", "FrontdoorWebApplicationFirewallLog")
  | extend details_data_s = column_ifexists("details_data_s", tostring(AdditionalFields.details_data))
  |where requestUri_s has_any (log4jioc) or details_message_s has_any (log4jioc) or details_data_s has_any (log4jioc)
  | extend Malicious = iff(isnotempty( details_data_s),details_data_s,iff(isnotempty( requestUri_s),requestUri_s,""))
  |parse Malicious with * '${' MaliciousCommand '}' * 
  | extend EncodeCmd = iff(MaliciousCommand has 'Base64/', split(split(MaliciousCommand, "Base64/",1)[0], "}", 0)[0], "")
  | extend EncodeCmd1 = iff(MaliciousCommand has 'base64/', split(split(MaliciousCommand, "base64/",1)[0], "}", 0)[0], "")
  | extend CmdLine = iff( isnotempty(EncodeCmd), EncodeCmd, EncodeCmd1)
  | extend DecodedCmdLine = base64_decode_tostring(tostring(CmdLine))
  | extend DecodedCmdLine = iff( isnotempty(DecodedCmdLine), DecodedCmdLine, "Unable to decode/Doesn't need decoding")
  | project TimeGenerated, Target=column_ifexists("hostname_s", tostring(AdditionalFields.hostname)), MaliciousHost = column_ifexists("clientIp_s", tostring(AdditionalFields.clientIp)) , MaliciousCommand, details_data_s = column_ifexists("details_data_s", tostring(AdditionalFields.details_data)), DecodedCmdLine, Message,
  ruleSetType_s = column_ifexists("ruleSetType_s", tostring(AdditionalFields.ruleSetType)), OperationName, SubscriptionId, details_message_s = column_ifexists("details_message_s", tostring(AdditionalFields.details_message)), 
  details_file_s = column_ifexists("details_message_s", tostring(AdditionalFields.details_file))
  | extend timestamp = TimeGenerated
entityMappings: 
- entityType: IP
  fieldMappings:
    - identifier: Address
      columnName: MaliciousHost
version: 1.0.4
kind: Scheduled

Stages and Predicates

Parameters

let log4jioc = dynamic(["jndi","ldap","${::"]);

Stage 1: `source`

AzureDiagnostics

Stage 2: `where`

| where ResourceProvider == "MICROSOFT.NETWORK" and Category in ("ApplicationGatewayFirewallLog", "FrontdoorWebApplicationFirewallLog")

Stage 3: `extend`

| extend details_data_s = column_ifexists("details_data_s", tostring(AdditionalFields.details_data))

Stage 4: `where`

| where requestUri_s has_any (log4jioc) or details_message_s has_any (log4jioc) or details_data_s has_any (log4jioc)

Stage 5: `extend`

| extend Malicious = iff(isnotempty( details_data_s),details_data_s,iff(isnotempty( requestUri_s),requestUri_s,""))

Malicious =

ifisnotempty(details_data_s)details_data_s

elseiff(isnotempty(requestUri_s), requestUri_s, "")

Stage 6: `parse`

| parse Malicious with * '${' MaliciousCommand '}' *

Stage 7: `extend` (5 consecutive steps)

| extend EncodeCmd = iff(MaliciousCommand has 'Base64/', split(split(MaliciousCommand, "Base64/",1)[0], "}", 0)[0], "")
| extend EncodeCmd1 = iff(MaliciousCommand has 'base64/', split(split(MaliciousCommand, "base64/",1)[0], "}", 0)[0], "")
| extend CmdLine = iff( isnotempty(EncodeCmd), EncodeCmd, EncodeCmd1)
| extend DecodedCmdLine = base64_decode_tostring(tostring(CmdLine))
| extend DecodedCmdLine = iff( isnotempty(DecodedCmdLine), DecodedCmdLine, "Unable to decode/Doesn't need decoding")

EncodeCmd =

ifMaliciousCommand has "Base64/"split(split(MaliciousCommand, "Base64/", 1)[0], "}", 0)[0]

else""

Stage 8: `project`

| project TimeGenerated, Target=column_ifexists("hostname_s", tostring(AdditionalFields.hostname)), MaliciousHost = column_ifexists("clientIp_s", tostring(AdditionalFields.clientIp)) , MaliciousCommand, details_data_s = column_ifexists("details_data_s", tostring(AdditionalFields.details_data)), DecodedCmdLine, Message,
ruleSetType_s = column_ifexists("ruleSetType_s", tostring(AdditionalFields.ruleSetType)), OperationName, SubscriptionId, details_message_s = column_ifexists("details_message_s", tostring(AdditionalFields.details_message)), 
details_file_s = column_ifexists("details_message_s", tostring(AdditionalFields.details_file))

Stage 9: `extend`

| extend timestamp = TimeGenerated

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
`Category`	in	`ApplicationGatewayFirewallLog` transforms: `cased` `FrontdoorWebApplicationFirewallLog` transforms: `cased`
`ResourceProvider`	eq	`MICROSOFT.NETWORK` transforms: `cased`
`details_data_s`	match	`${::` `jndi` `ldap`
`details_message_s`	match	`${::` `jndi` `ldap`
`requestUri_s`	match	`${::` `jndi` `ldap`

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
`DecodedCmdLine`	`project`
`MaliciousCommand`	`project`
`MaliciousHost`	`project`
`Message`	`project`
`OperationName`	`project`
`SubscriptionId`	`project`
`Target`	`project`
`TimeGenerated`	`project`
`details_data_s`	`project`
`details_file_s`	`project`
`details_message_s`	`project`
`ruleSetType_s`	`project`
`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)

Azure WAF matching for Log4j vuln(CVE-2021-44228)

MITRE ATT&CK coverage

Rule body kusto

Stages and Predicates

Parameters

Stage 1: `source`

Stage 2: `where`

Stage 3: `extend`

Stage 4: `where`

Stage 5: `extend`

Stage 6: `parse`

Stage 7: `extend` (5 consecutive steps)

Stage 8: `project`

Stage 9: `extend`

Indicators

Output fields

Keyboard shortcuts

Search operators

Azure WAF matching for Log4j vuln(CVE-2021-44228)

MITRE ATT&CK coverage

Rule body kusto

Stages and Predicates

Parameters

Stage 1: source

Stage 2: where

Stage 3: extend

Stage 4: where

Stage 5: extend

Stage 6: parse

Stage 7: extend (5 consecutive steps)

Stage 8: project

Stage 9: extend

Indicators

Output fields

Stage 1: `source`

Stage 2: `where`

Stage 3: `extend`

Stage 4: `where`

Stage 5: `extend`

Stage 6: `parse`

Stage 7: `extend` (5 consecutive steps)

Stage 8: `project`

Stage 9: `extend`