T1534 — Internal Spearphishing

# T1534 - Internal Spearphishing

## SOC Recommendation
Investigate Internal Spearphishing activity in the context of Lateral Movement: confirm scope, affected host/identity, and whether it matches expected administrative behaviour before deciding this is benign.

## D3FEND Mappings
| D3FEND Technique | Relationship | Practical SOC Action |
|---|---|---|
| File Analysis | Detect | Monitor for File Analysis indicators relevant to this technique. |
| File Encryption | Harden | Apply File Encryption to reduce this technique's viability before an incident occurs. |
| File Eviction | Evict | Use File Eviction to remove the adversary's foothold once this technique is confirmed. |
| Content Filtering | Isolate | Apply Content Filtering to contain the blast radius once this technique is observed. |

## Investigation Steps
1. Review Defender for Endpoint / Defender XDR alerts and timeline for the affected host or identity.
2. Check Sentinel analytics rules and incidents correlated with this technique.
3. Review Entra ID sign-in and audit logs if the technique involves an identity or cloud resource.

## Evidence to Collect
- Host or resource affected
- Account or identity involved
- Timestamp of the activity
- Related process, file, or network artifact
- Any preceding or follow-on alerts

## Response Actions
| Action | Risk | Automation Safe | Approval Required |
|---|---|---|---|
| Contain the affected host or account | Medium | No | Yes |
| Collect and preserve evidence | Low | Yes | No |

## KQL
```kql
MimecastCG
| where Type == "email_iep"
| extend  SenderEnvelope = ['Sender Envelope']  , MessageId = ['Message ID']
```
```kql
MimecastSIEM_CL| where mimecastEventId_s=="mail_ttp_iep"
```
```kql
////////////
// threshold = If the number of unique accounts that a power app is shared with is greater than
// threshold than it'll trigger an alert. A threshold of 5 is good to start with.
// However, if this is giving too many false positives, please adjust the threshold.
////////////
let threshold = 5;
////////////
// Please replace the allowed_domains with a list of domains of your partners/sibling orgs
// with whom you generally share power apps with. This will allow us to filter
// legitimate bulk sharing attempts. Avoid using domains such as gmail, outlook, etc.
///////////
let allowed_domains = pack_array("contoso.com");
let query_frequency = 1h;
let query_lookback = 14d;
PowerPlatformAdminActivity
| where TimeGenerated >= ago(query_frequency)
| where EventOriginalType == "PowerAppPermissionEdited"
| extend Properties = tostring(PropertyCollection)
| extend AppId = extract(@'"powerplatform.analytics.resource.power_app.id","Value":"([^"]+)"', 1, Properties)
| extend AppId = tolower(replace_string(AppId, '/providers/Microsoft.PowerApps/apps/', ''))
| extend TargetPrincipalId = extract(@'"targetuser.id","Value":"([^"]+)"', 1, Properties)
| join kind=leftouter (
    AuditLogs
    | where ActivityDateTime >= ago(query_lookback)
    | where SourceSystem =~ "Azure AD" and OperationName == "Invite external user"
    | where Result =~ "success"
    | extend InvitedOrgEmail = tostring(parse_json(AdditionalDetails[5])['value'])
    | extend InvitedOrgDomain = tostring(split(InvitedOrgEmail, "@")[1])
    | where not(InvitedOrgDomain has_any(allowed_domains))
    | extend
        InvitedById = tostring(parse_json(InitiatedBy)['user']['id']),
        InvitedByUPN = tostring(parse_json(InitiatedBy)['user']['userPrincipalName']),
        InvitedEmail = tostring(parse_json(TargetResources[0])['userPrincipalName']),
        InvitedId = tostring(parse_json(TargetResources[0])['id'])
    | summarize by InvitedById, InvitedByUPN, InvitedEmail, InvitedId, InvitedOrgDomain)
    on $left.TargetPrincipalId == $right.InvitedId
| where isnotempty(InvitedId)
| summarize
    StartTime = min(TimeGenerated),
    EndTime = max(TimeGenerated),
    TargetedUsersCount=dcount(TargetPrincipalId),
    TargetedObjectIds = make_set(TargetPrincipalId, 1000),
    InvitedDomains = make_set(InvitedOrgDomain, 1000),
    InvitedEmailAddresses = make_set(InvitedEmail, 1000)
    by AppId, InvitedById, InvitedByUPN
| extend
    PowerAppsEntityId = 27593,
    AccountName = tostring(split(InvitedByUPN, '@')[0]),
    UPNSuffix = tostring(split(InvitedByUPN, '@')[1])
| project
    StartTime,
    EndTime,
    InvitedByUPN,
    InvitedById,
    InvitedDomains,
    InvitedEmailAddresses,
    TargetedUsersCount,
    TargetedObjectIds,
    AppId,
    PowerAppsEntityId,
    AccountName,
    UPNSuffix
```

## Escalation Criteria
- Internal Spearphishing activity observed on a privileged account or critical system.
- Activity follows or precedes other suspicious behaviour in the same investigation.
- Automated triage cannot confidently rule out malicious intent.

## False Positive Considerations
- Legitimate administrative or maintenance activity matching this pattern.
- Approved security testing or red team exercise.
- Known benign software producing similar telemetry.

Generated by SOC Response Atlas by Basyrix.

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• /api/techniques/T1534.json
• /api/recommendations/T1534.json
• /api/d3fend/T1534.json
• /api/mappings/T1534.json
• /api/confluence/T1534.md

Example curl:

curl https://atlas.basyrix.com/api/recommendations/T1534.json

Response:

{
  "technique_id": "T1534",
  "name": "Internal Spearphishing",
  "priority": "high",
  "status": "draft",
  "version": "0.1.0",
  "last_reviewed": "2026-07-23",
  "generated_by": "SOC Response Atlas by Basyrix",
  "tactics": [
    "Lateral Movement"
  ],
  "platforms": [
    "Linux",
    "macOS",
    "Office Suite",
    "SaaS",
    "Windows"
  ],
  "summary": "After they already have access to accounts or systems within the environment, adversaries may use internal spearphishing to gain access to additional information or compromise other users within the same organization. Internal spearphishing is multi-staged campaign where a legitimate account is initially compromised either by controlling the user's device or by compromising the account credentials of the user...",
  "soc_recommendation": "Investigate Internal Spearphishing activity in the context of Lateral Movement: confirm scope, affected host/identity, and whether it matches expected administrative behaviour before deciding this is benign.",
  "d3fend_mappings": [
    {
      "id": "D3-FA",
      "name": "File Analysis",
      "relationship": "detect",
      "practical_action": "Monitor for File Analysis indicators relevant to this technique.",
      "tooling": [
        "Defender for Endpoint"
      ]
    },
    {
      "id": "D3-FE",
      "name": "File Encryption",
      "relationship": "harden",
      "practical_action": "Apply File Encryption to reduce this technique's viability before an incident occurs.",
      "tooling": [
        "Defender for Endpoint"
      ]
    },
    {
      "id": "D3-FEV",
      "name": "File Eviction",
      "relationship": "evict",
      "practical_action": "Use File Eviction to remove the adversary's foothold once this technique is confirmed.",
      "tooling": [
        "Defender for Endpoint"
      ]
    },
    {
      "id": "D3-CF",
      "name": "Content Filtering",
      "relationship": "isolate",
      "practical_action": "Apply Content Filtering to contain the blast radius once this technique is observed.",
      "tooling": [
        "Defender for Endpoint"
      ]
    }
  ],
  "investigation_steps": {
    "microsoft": [
      "Review Defender for Endpoint / Defender XDR alerts and timeline for the affected host or identity.",
      "Check Sentinel analytics rules and incidents correlated with this technique.",
      "Review Entra ID sign-in and audit logs if the technique involves an identity or cloud resource."
    ],
    "generic": [
      "Confirm whether the observed internal spearphishing activity matches expected administrative or application behaviour.",
      "Identify the host, account, or resource where the activity occurred and its business criticality.",
      "Check for related alerts before and after this activity to reconstruct the broader intrusion timeline.",
      "Real detection reference: \"Mimecast Secure Email Gateway - Internal Email Protect\" -- Detects threats from internal email threat protection.'"
    ]
  },
  "evidence_to_collect": [
    "Host or resource affected",
    "Account or identity involved",
    "Timestamp of the activity",
    "Related process, file, or network artifact",
    "Any preceding or follow-on alerts"
  ],
  "response_actions": [
    {
      "name": "Contain the affected host or account",
      "category": "Containment",
      "risk": "Medium",
      "automation_safe": false,
      "approval_required": true,
      "tool": "Defender for Endpoint / Entra ID",
      "notes": "Requires approval -- confirm malicious intent before isolating a host or disabling an account."
    },
    {
      "name": "Collect and preserve evidence",
      "category": "Investigation",
      "risk": "Low",
      "automation_safe": true,
      "approval_required": false,
      "tool": "Defender for Endpoint",
      "notes": "Safe -- read-only evidence collection."
    }
  ],
  "queries": {
    "kql": [
      {
        "name": "d3bd7640-3600-49f9-8d10-6fe312e68b4f — Mimecast Secure Email Gateway - Internal Email Protect",
        "description": "Detects threats from internal email threat protection.' (Source: Microsoft's official Azure-Sentinel Detections (MIT licensed).)",
        "query": "MimecastCG\n| where Type == \"email_iep\"\n| extend  SenderEnvelope = ['Sender Envelope']  , MessageId = ['Message ID']"
      },
      {
        "name": "5b66d176-e344-4abf-b915-e5f09a6430ef — Mimecast Secure Email Gateway - Internal Email Protect",
        "description": "Detects threats from internal email threat protection (Source: Microsoft's official Azure-Sentinel Detections (MIT licensed).)",
        "query": "MimecastSIEM_CL| where mimecastEventId_s==\"mail_ttp_iep\""
      },
      {
        "name": "943acfa0-9285-4eb0-a9c0-42e36177ef19 — Power Apps - Bulk sharing of Power Apps to newly created guest users",
        "description": "Identifies unusual bulk sharing, based on a predefined threshold in the query, of Power Apps to newly created Microsoft Entra guest users. (Source: Microsoft's official Azure-Sentinel Detections (MIT licensed).)",
        "query": "////////////\n// threshold = If the number of unique accounts that a power app is shared with is greater than\n// threshold than it'll trigger an alert. A threshold of 5 is good to start with.\n// However, if this is giving too many false positives, please adjust the threshold.\n////////////\nlet threshold = 5;\n////////////\n// Please replace the allowed_domains with a list of domains of your partners/sibling orgs\n// with whom you generally share power apps with. This will allow us to filter\n// legitimate bulk sharing attempts. Avoid using domains such as gmail, outlook, etc.\n///////////\nlet allowed_domains = pack_array(\"contoso.com\");\nlet query_frequency = 1h;\nlet query_lookback = 14d;\nPowerPlatformAdminActivity\n| where TimeGenerated >= ago(query_frequency)\n| where EventOriginalType == \"PowerAppPermissionEdited\"\n| extend Properties = tostring(PropertyCollection)\n| extend AppId = extract(@'\"powerplatform.analytics.resource.power_app.id\",\"Value\":\"([^\"]+)\"', 1, Properties)\n| extend AppId = tolower(replace_string(AppId, '/providers/Microsoft.PowerApps/apps/', ''))\n| extend TargetPrincipalId = extract(@'\"targetuser.id\",\"Value\":\"([^\"]+)\"', 1, Properties)\n| join kind=leftouter (\n    AuditLogs\n    | where ActivityDateTime >= ago(query_lookback)\n    | where SourceSystem =~ \"Azure AD\" and OperationName == \"Invite external user\"\n    | where Result =~ \"success\"\n    | extend InvitedOrgEmail = tostring(parse_json(AdditionalDetails[5])['value'])\n    | extend InvitedOrgDomain = tostring(split(InvitedOrgEmail, \"@\")[1])\n    | where not(InvitedOrgDomain has_any(allowed_domains))\n    | extend\n        InvitedById = tostring(parse_json(InitiatedBy)['user']['id']),\n        InvitedByUPN = tostring(parse_json(InitiatedBy)['user']['userPrincipalName']),\n        InvitedEmail = tostring(parse_json(TargetResources[0])['userPrincipalName']),\n        InvitedId = tostring(parse_json(TargetResources[0])['id'])\n    | summarize by InvitedById, InvitedByUPN, InvitedEmail, InvitedId, InvitedOrgDomain)\n    on $left.TargetPrincipalId == $right.InvitedId\n| where isnotempty(InvitedId)\n| summarize\n    StartTime = min(TimeGenerated),\n    EndTime = max(TimeGenerated),\n    TargetedUsersCount=dcount(TargetPrincipalId),\n    TargetedObjectIds = make_set(TargetPrincipalId, 1000),\n    InvitedDomains = make_set(InvitedOrgDomain, 1000),\n    InvitedEmailAddresses = make_set(InvitedEmail, 1000)\n    by AppId, InvitedById, InvitedByUPN\n| extend\n    PowerAppsEntityId = 27593,\n    AccountName = tostring(split(InvitedByUPN, '@')[0]),\n    UPNSuffix = tostring(split(InvitedByUPN, '@')[1])\n| project\n    StartTime,\n    EndTime,\n    InvitedByUPN,\n    InvitedById,\n    InvitedDomains,\n    InvitedEmailAddresses,\n    TargetedUsersCount,\n    TargetedObjectIds,\n    AppId,\n    PowerAppsEntityId,\n    AccountName,\n    UPNSuffix"
      }
    ],
    "spl": [],
    "esql": [
      {
        "name": "2112ecce-cd34-11ef-873f-f661ea17fbcd — AWS SNS Topic Message Publish by Rare User",
        "description": "(KUERY) Identifies when an SNS topic message is published by a rare user in AWS. Adversaries may publish messages to SNS topics for phishing campaigns, data exfiltration, or lateral movement within the AWS environment... (Source: Elastic's official detection-rules repository (Elastic License v2).)",
        "query": "data_stream.dataset:\"aws.cloudtrail\"\n    and event.provider:\"sns.amazonaws.com\"\n    and event.action:\"Publish\"\n    and event.outcome:\"success\""
      }
    ]
  },
  "automation": {
    "safe": [
      "Add recommendation as Sentinel incident comment.",
      "Run enrichment queries.",
      "Create ServiceNow SecOps task."
    ],
    "approval_required": [
      "Contain or disable the affected host/account.",
      "Any change to production configuration."
    ]
  },
  "escalation_criteria": [
    "Internal Spearphishing activity observed on a privileged account or critical system.",
    "Activity follows or precedes other suspicious behaviour in the same investigation.",
    "Automated triage cannot confidently rule out malicious intent."
  ],
  "false_positive_considerations": [
    "Legitimate administrative or maintenance activity matching this pattern.",
    "Approved security testing or red team exercise.",
    "Known benign software producing similar telemetry."
  ],
  "confluence": {
    "title": "T1534 - Internal Spearphishing Response Guidance",
    "labels": [
      "mitre",
      "attack",
      "d3fend",
      "secops",
      "basyrix"
    ],
    "sections": [
      "summary",
      "d3fend_mappings",
      "investigation_steps",
      "response_actions",
      "queries",
      "automation",
      "escalation_criteria",
      "false_positive_considerations"
    ]
  }
}