User agent search for log4j exploitation attempt

Status: available
Severity: high
Time window: 1d
Group by: Account, AppDisplayName, ClientAppUsed, DstIpAddr, EventName, HttpStatus, HttpUserAgent, Operation, ResourceId, ResourceType, SourceIP, Type, Url, UserAgent, csMethod, ruleName_s, sSiteName
Source: github.com/Azure/Azure-Sentinel

'This query uses various log sources having user agent data to look for log4j CVE-2021-44228 exploitation attempt based on user agent pattern. Log4j is an open-source Apache logging library that is used in many Java-based applications. The regex and the string matching look for the most common attacks. This might not be comprehensive to detect every possible user agent variation. Reference: https://msrc-blog.microsoft.com/2021/12/11/microsofts-response-to-cve-2021-44228-apache-log4j2/'

MITRE ATT&CK coverage

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

Rule body kusto

id: 29283b22-a1c0-4d16-b0a9-3460b655a46a
name: User agent search for log4j exploitation attempt
description: |
  'This query uses various log sources having user agent data to look for log4j CVE-2021-44228 exploitation attempt based on user agent pattern.
  Log4j is an open-source Apache logging library that is used in many Java-based applications. The regex and the string matching look for the most common attacks. This might not be comprehensive to detect every possible user agent variation.
   Reference: https://msrc-blog.microsoft.com/2021/12/11/microsofts-response-to-cve-2021-44228-apache-log4j2/'
severity: High
status: Available
requiredDataConnectors:
  - connectorId: SquidProxy
    dataTypes:
      - SquidProxy_CL
  - connectorId: Zscaler
    dataTypes:
      - CommonSecurityLog
  - connectorId: WAF
    dataTypes:
      - AzureDiagnostics
  - connectorId: Office365
    dataTypes:
      - OfficeActivity
  - connectorId: AzureActiveDirectory
    dataTypes:
      - SigninLogs
  - connectorId: AzureActiveDirectory
    dataTypes:
      - AADNonInteractiveUserSignInLogs
  - connectorId: AWS
    dataTypes:
      - AWSCloudTrail
  - connectorId: AzureMonitor(IIS)
    dataTypes:
      - W3CIISLog
queryFrequency: 1d
queryPeriod: 1d
triggerOperator: gt
triggerThreshold: 0
tactics:
  - InitialAccess
relevantTechniques:
  - T1190
tags:
    - log4j
    - log4shell
    - CVE2021-44228
    - Schema: ASimWebSession
    - SchemaVersion: 0.2.1
    - Schema: ASimNetworkSessions
    - SchemaVersion: 0.2.1
query: |
  let UserAgentString = dynamic (["${jndi:ldap:/", "${jndi:rmi:/", "${jndi:ldaps:/", "${jndi:dns:/", "${jndi:iiop:/","${jndi:","${jndi:nds:/","${jndi:corba/"]);
  let UARegexMinimalString=dynamic(['{','%7b', '%7B']);
  let UARegex = @'(\\$|%24)(\\{|%7B)([^jJ]*[jJ])([^nN]*[nN])([^dD]*[dD])([^iI]*[iI])(:|%3A|\\$|%24|}|%7D)';
  (union isfuzzy=true
  (OfficeActivity
  | where UserAgent has_any (UserAgentString) or UserAgent matches regex UARegex
  | summarize StartTime = min(TimeGenerated), EndTime = max(TimeGenerated) by UserAgent, SourceIP = ClientIP, Account = UserId, Type, Operation
  ),
  (AzureDiagnostics
  | where Category in ("FrontdoorWebApplicationFirewallLog", "FrontdoorAccessLog", "ApplicationGatewayFirewallLog", "ApplicationGatewayAccessLog")
  | where userAgent_s has_any (UserAgentString) or userAgent_s matches regex UARegex
  | summarize StartTime = min(TimeGenerated), EndTime = max(TimeGenerated) by UserAgent = userAgent_s, SourceIP = column_ifexists("clientIp_s",clientIP_s), Type, column_ifexists("originalHost_s",host_s), Url = requestUri_s, HttpStatus = column_ifexists("httpStatusDetails_s",httpStatus_d), column_ifexists("trackingReference_s",transactionId_g), ruleName_s, ResourceType, ResourceId
  ),
  (
  W3CIISLog
  | where csUserAgent has_any (UserAgentString) or csUserAgent matches regex UARegex
  | summarize StartTime = min(TimeGenerated), EndTime = max(TimeGenerated) by UserAgent = csUserAgent, SourceIP = cIP, Account = csUserName, Type, sSiteName, csMethod, Url = csUriStem
  ),
  (
  AWSCloudTrail
  | where UserAgent has_any (UserAgentString) or UserAgent matches regex UARegex
  | summarize StartTime = min(TimeGenerated), EndTime = max(TimeGenerated) by UserAgent, SourceIP = SourceIpAddress, Account = UserIdentityUserName, Type, EventName
  ),
  (SigninLogs
  | where UserAgent has_any (UserAgentString) or UserAgent matches regex UARegex
  | summarize StartTime = min(TimeGenerated), EndTime = max(TimeGenerated) by UserAgent, SourceIP = IPAddress, Account = UserPrincipalName, Type, Operation = OperationName, tostring(LocationDetails), tostring(DeviceDetail),    AppDisplayName, ClientAppUsed
  ),
  (AADNonInteractiveUserSignInLogs 
  | where UserAgent has_any (UserAgentString) or UserAgent matches regex UARegex
  | summarize StartTime = min(TimeGenerated), EndTime = max(TimeGenerated) by UserAgent, SourceIP = IPAddress, Account = UserPrincipalName, Type, Operation = OperationName, tostring(LocationDetails), tostring(DeviceDetail), AppDisplayName, ClientAppUsed
  ),
  (_Im_WebSession (httpuseragent_has_any=array_concat(UserAgentString,UARegexMinimalString))
  | where HttpUserAgent has_any (UserAgentString) or HttpUserAgent matches regex UARegex
  | summarize StartTime = min(TimeGenerated), EndTime = max(TimeGenerated) by HttpUserAgent, SourceIP = SrcIpAddr, DstIpAddr, Account = SrcUsername, Url, Type
  )
  )
entityMappings:
  - entityType: URL
    fieldMappings:
      - identifier: Url
        columnName: Url
  - entityType: IP
    fieldMappings:
      - identifier: Address
        columnName: SourceIP
  - entityType: Account
    fieldMappings:
      - identifier: Name
        columnName: Account
version: 1.0.9
kind: Scheduled

Stages and Predicates

Parameters

let UserAgentString = dynamic (["${jndi:ldap:/", "${jndi:rmi:/", "${jndi:ldaps:/", "${jndi:dns:/", "${jndi:iiop:/","${jndi:","${jndi:nds:/","${jndi:corba/"]);
let UARegexMinimalString = dynamic(['{','%7b', '%7B']);

Let binding: `UARegex`

let UARegex = @'(\\$|%24)(\\{|%7B)([^jJ]*[jJ])([^nN]*[nN])([^dD]*[dD])([^iI]*[iI])(:|%3A|\\$|%24|}|%7D)';

union `isfuzzy=true` (7 sources)

Each leg below queries one source; the rule matches if any leg does. Sources: OfficeActivity, AzureDiagnostics, W3CIISLog, AWSCloudTrail, SigninLogs, AADNonInteractiveUserSignInLogs, _Im_WebSession

Leg 1: `OfficeActivity`

OfficeActivity
| where UserAgent has_any (UserAgentString) or UserAgent matches regex UARegex
| summarize StartTime = min(TimeGenerated), EndTime = max(TimeGenerated) by UserAgent, SourceIP = ClientIP, Account = UserId, Type, Operation

Leg 2: `AzureDiagnostics`

AzureDiagnostics
| where Category in ("FrontdoorWebApplicationFirewallLog", "FrontdoorAccessLog", "ApplicationGatewayFirewallLog", "ApplicationGatewayAccessLog")
| where userAgent_s has_any (UserAgentString) or userAgent_s matches regex UARegex
| summarize StartTime = min(TimeGenerated), EndTime = max(TimeGenerated) by UserAgent = userAgent_s, SourceIP = column_ifexists("clientIp_s",clientIP_s), Type, column_ifexists("originalHost_s",host_s), Url = requestUri_s, HttpStatus = column_ifexists("httpStatusDetails_s",httpStatus_d), column_ifexists("trackingReference_s",transactionId_g), ruleName_s, ResourceType, ResourceId

Leg 3: `W3CIISLog`

W3CIISLog
| where csUserAgent has_any (UserAgentString) or csUserAgent matches regex UARegex
| summarize StartTime = min(TimeGenerated), EndTime = max(TimeGenerated) by UserAgent = csUserAgent, SourceIP = cIP, Account = csUserName, Type, sSiteName, csMethod, Url = csUriStem

Leg 4: `AWSCloudTrail`

AWSCloudTrail
| where UserAgent has_any (UserAgentString) or UserAgent matches regex UARegex
| summarize StartTime = min(TimeGenerated), EndTime = max(TimeGenerated) by UserAgent, SourceIP = SourceIpAddress, Account = UserIdentityUserName, Type, EventName

Leg 5: `SigninLogs`

SigninLogs
| where UserAgent has_any (UserAgentString) or UserAgent matches regex UARegex
| summarize StartTime = min(TimeGenerated), EndTime = max(TimeGenerated) by UserAgent, SourceIP = IPAddress, Account = UserPrincipalName, Type, Operation = OperationName, tostring(LocationDetails), tostring(DeviceDetail),    AppDisplayName, ClientAppUsed

Leg 6: `AADNonInteractiveUserSignInLogs`

AADNonInteractiveUserSignInLogs 
| where UserAgent has_any (UserAgentString) or UserAgent matches regex UARegex
| summarize StartTime = min(TimeGenerated), EndTime = max(TimeGenerated) by UserAgent, SourceIP = IPAddress, Account = UserPrincipalName, Type, Operation = OperationName, tostring(LocationDetails), tostring(DeviceDetail), AppDisplayName, ClientAppUsed

Leg 7: `_Im_WebSession`

_Im_WebSession (httpuseragent_has_any=array_concat(UserAgentString,UARegexMinimalString))
| where HttpUserAgent has_any (UserAgentString) or HttpUserAgent matches regex UARegex
| summarize StartTime = min(TimeGenerated), EndTime = max(TimeGenerated) by HttpUserAgent, SourceIP = SrcIpAddr, DstIpAddr, Account = SrcUsername, Url, Type

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	`ApplicationGatewayAccessLog` transforms: `cased` `ApplicationGatewayFirewallLog` transforms: `cased` `FrontdoorAccessLog` transforms: `cased` `FrontdoorWebApplicationFirewallLog` transforms: `cased`
`HttpUserAgent`	match	`${jndi:` `${jndi:corba/` `${jndi:dns:/` `${jndi:iiop:/` `${jndi:ldap:/` `${jndi:ldaps:/` `${jndi:nds:/` `${jndi:rmi:/`
`HttpUserAgent`	regex_match	`(\$\|%24)(\{\|%7B)([^jJ][jJ])([^nN][nN])([^dD][dD])([^iI][iI])(:\|%3A\|\$\|%24\|}\|%7D)`
`UserAgent`	match	`${jndi:` `${jndi:corba/` `${jndi:dns:/` `${jndi:iiop:/` `${jndi:ldap:/` `${jndi:ldaps:/` `${jndi:nds:/` `${jndi:rmi:/`
`UserAgent`	regex_match	`(\$\|%24)(\{\|%7B)([^jJ][jJ])([^nN][nN])([^dD][dD])([^iI][iI])(:\|%3A\|\$\|%24\|}\|%7D)`
`csUserAgent`	match	`${jndi:` `${jndi:corba/` `${jndi:dns:/` `${jndi:iiop:/` `${jndi:ldap:/` `${jndi:ldaps:/` `${jndi:nds:/` `${jndi:rmi:/`
`csUserAgent`	regex_match	`(\$\|%24)(\{\|%7B)([^jJ][jJ])([^nN][nN])([^dD][dD])([^iI][iI])(:\|%3A\|\$\|%24\|}\|%7D)`
`userAgent_s`	match	`${jndi:` `${jndi:corba/` `${jndi:dns:/` `${jndi:iiop:/` `${jndi:ldap:/` `${jndi:ldaps:/` `${jndi:nds:/` `${jndi:rmi:/`
`userAgent_s`	regex_match	`(\$\|%24)(\{\|%7B)([^jJ][jJ])([^nN][nN])([^dD][dD])([^iI][iI])(:\|%3A\|\$\|%24\|}\|%7D)`

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
`Account`	`summarize`
`DstIpAddr`	`summarize`
`EndTime`	`summarize`
`HttpUserAgent`	`summarize`
`SourceIP`	`summarize`
`StartTime`	`summarize`
`Type`	`summarize`
`Url`	`summarize`

`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)

User agent search for log4j exploitation attempt

MITRE ATT&CK coverage

Rule body kusto

Stages and Predicates

Parameters

Let binding: `UARegex`

union `isfuzzy=true` (7 sources)

Leg 1: `OfficeActivity`

Leg 2: `AzureDiagnostics`

Leg 3: `W3CIISLog`

Leg 4: `AWSCloudTrail`

Leg 5: `SigninLogs`

Leg 6: `AADNonInteractiveUserSignInLogs`

Leg 7: `_Im_WebSession`

Indicators

Output fields

Keyboard shortcuts

Search operators

User agent search for log4j exploitation attempt

MITRE ATT&CK coverage

Rule body kusto

Stages and Predicates

Parameters

Let binding: UARegex

union isfuzzy=true (7 sources)

Leg 1: OfficeActivity

Leg 2: AzureDiagnostics

Leg 3: W3CIISLog

Leg 4: AWSCloudTrail

Leg 5: SigninLogs

Leg 6: AADNonInteractiveUserSignInLogs

Leg 7: _Im_WebSession

Indicators

Output fields

Let binding: `UARegex`

union `isfuzzy=true` (7 sources)

Leg 1: `OfficeActivity`

Leg 2: `AzureDiagnostics`

Leg 3: `W3CIISLog`

Leg 4: `AWSCloudTrail`

Leg 5: `SigninLogs`

Leg 6: `AADNonInteractiveUserSignInLogs`

Leg 7: `_Im_WebSession`