Microsoft Sentinel high experimental kql

User agent search for log4j exploitation attempt

'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/'

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Detection Logic

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
)
)

Field Validations

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