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id: e1f2a3b4-c5d6-4e7f-8a9b-0c1d2e3f4a5b
name: "SigninLogs — Conditional Access Policy Blocked then Successful Bypass"
version: 1.0.0
kind: Scheduled
description: |
  Detects a user blocked by Conditional Access (ResultType 53003) who then achieves a successful sign-in within 4 hours — possibly via a legacy auth client that bypasses CA, an unmanaged device, or a CA policy gap. MITRE ATT&CK: T1078 (Valid Accounts), T1562.001 (Disable or Modify Tools).
severity: High
requiredDataConnectors:
  - connectorId: AzureActiveDirectory
    dataTypes:
      - SigninLogs
queryFrequency: PT4H
queryPeriod: PT4H
triggerOperator: gt
triggerThreshold: 0
tactics:
  - DefenseEvasion
  - InitialAccess
relevantTechniques:
  - T1078
  - T1562
query: |

    // ---- Network Allowlist (exclude trusted IPs / CIDR / ranges) --------------
    let _allow = materialize(union isfuzzy=true (print R="" | take 0), (_GetWatchlist('NetworkAllowlist') | project R = tostring(IPOrRange)) | where isnotempty(R));
    let _allowCIDR  = toscalar(_allow | where not(R matches regex @'^\d+\.\d+\.\d+\.\d+-\d+\.\d+\.\d+\.\d+$') | extend R = iff(R has '/', R, strcat(R, '/32')) | summarize make_list(R));
    let _allowRange = toscalar(_allow | where R matches regex @'^\d+\.\d+\.\d+\.\d+-\d+\.\d+\.\d+\.\d+$' | summarize make_list(R));
    let _ExcludeAllowlistedIPs = (T:(IPAddress:string)) {
        T
        | extend IPAddress = tostring(IPAddress)
        | where array_length(_allowCIDR) == 0 or isnull(ipv4_is_in_any_range(IPAddress, _allowCIDR)) or not(ipv4_is_in_any_range(IPAddress, _allowCIDR))
        | mv-apply _r = _allowRange to typeof(string) on (
            extend _lo = tostring(split(_r,'-')[0]), _hi = tostring(split(_r,'-')[1])
            | extend _inRange = ipv4_compare(IPAddress, _lo) >= 0 and ipv4_compare(IPAddress, _hi) <= 0
            | summarize _anyInRange = max(toint(_inRange)))
        | where isnull(_anyInRange) or _anyInRange == 0
        | project-away _anyInRange
    };
    // ---------------------------------------------------------------------------
    let lookback     = 4h;
    let bypassWindow = 4h;
    let CABlockedUsers =
        SigninLogs
        | invoke _ExcludeAllowlistedIPs()
        | where TimeGenerated > ago(lookback)
        | where ResultType == "53003"
        | summarize
            BlockedCount = count(),
            LastBlocked  = max(TimeGenerated),
            BlockedIPs   = make_set(IPAddress, 5),
            BlockedApps  = make_set(AppDisplayName, 5)
          by UserPrincipalName;
    SigninLogs
    | invoke _ExcludeAllowlistedIPs()
    | where TimeGenerated > ago(lookback)
    | where ResultType == "0"
    | join kind=inner CABlockedUsers on UserPrincipalName
    | where TimeGenerated > LastBlocked
    | where TimeGenerated - LastBlocked <= bypassWindow
    | extend MinutesAfterBlock = datetime_diff("minute", TimeGenerated, LastBlocked)
    | project
        TimeGenerated, UserPrincipalName,
        IPAddress, Location, AppDisplayName,
        ClientAppUsed, ConditionalAccessStatus,
        RiskLevelDuringSignIn, BlockedCount,
        BlockedIPs, LastBlocked, MinutesAfterBlock
entityMappings:
  - entityType: Account
    fieldMappings:
      - identifier: FullName
        columnName: UserPrincipalName
  - entityType: IP
    fieldMappings:
      - identifier: Address
        columnName: IPAddress
customDetails:
  BlockedCount: BlockedCount
  MinutesAfterBlock: MinutesAfterBlock
alertDetailsOverride:
  alertDisplayNameFormat: "CA Policy Bypass — {{UserPrincipalName}} succeeded {{MinutesAfterBlock}}m after {{BlockedCount}} CA blocks"
  alertDescriptionFormat: "User {{UserPrincipalName}} was CA-blocked {{BlockedCount}} times then authenticated successfully {{MinutesAfterBlock}} minutes later — possible legacy auth or unmanaged device bypass."
incidentConfiguration:
  createIncident: true
  groupingConfiguration:
    enabled: true
    reopenClosedIncident: false
    lookbackDuration: PT4H
    matchingMethod: AllEntities
    groupByEntities:
  - Account
  - IP