Cross-source coverage

T1534 / ATT&CK

Internal Spearphishing

2 rules across 2 sources.

From MITRE ATT&CK 19.2

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. Adversaries may then attempt to take advantage of the trusted internal account to increase the likelihood of tricking more victims into falling for phish attempts, often incorporating Impersonation.

For example, adversaries may leverage Spearphishing Attachment or Spearphishing Link as part of internal spearphishing to deliver a payload or redirect to an external site to capture credentials through Input Capture on sites that mimic login interfaces.

Adversaries may also leverage internal chat apps, such as Microsoft Teams, to spread malicious content or engage users in attempts to capture sensitive information and/or credentials.

Platforms
Linux · macOS · Office Suite · SaaS · Windows
Telemetry
WinEventLog:Securitym365:unifiedWinEventLog:Sysmonauditd:SYSCALLApplication:Maillinux:syslogmacos:unifiedlogsaas:slack

How MITRE says to detect it DET0054

Internal Spearphishing via Trusted Accounts

Windows Analytic 0147

Sequence of internal email sent from a recently compromised user account (preceded by abnormal logon or device activity), with attachments or links leading to execution or credential harvesting. Defender observes: internal mail delivery to peers with high entropy attachments, followed by click events, process initiation, or credential prompts.

  • WinEventLog:Security EventCode=4624, 4648
  • WinEventLog:Security EventCode=4625
  • WinEventLog:Security EventCode=4672
  • m365:unified SendOnBehalf, MessageSend, ClickThrough, MailItemsAccessed
  • WinEventLog:Sysmon EventCode=1

Linux Analytic 0148

Delivery of suspicious internal communication (e.g., Thunderbird, Evolution) using compromised internal accounts. Sequence of: unexpected user activity + mail transfer logs + download or execution of attachments.

  • auditd:SYSCALL execve
  • Application:Mail smtpd$.*$: .*from=[.*@internaldomain.com](mailto:.*@internaldomain.com) to=[.*@internaldomain.com](mailto:.*@internaldomain.com)
  • linux:syslog curl|wget|python .*http

macOS Analytic 0149

Abnormal Apple Mail use, including internal email relays followed by file execution or script events (e.g., attachments launched via Preview, terminal triggered from Mail.app)

  • macos:unifiedlog com.apple.mail.* exec.*
  • macos:unifiedlog curl|osascript.*open location

SaaS Analytic 0150

Internal spearphishing via SaaS applications (e.g., Slack, Teams, Gmail): message sent from compromised user with attachment or URL, followed by click and credential access behavior.

  • saas:slack file_upload, message_send, message_click

Office Suite Analytic 0151

Outlook or Word used to forward suspicious internal attachments with macro content. Defender observes attachment forwarding, auto-opening behaviors, or macro prompt interactions.

  • m365:unified SendOnBehalf, MessageSend, AttachmentPreviewed
  • WinEventLog:Security EventCode=4103, 4104, 4105, 4106

View on attack.mitre.org ↗

Azure/Azure-Sentinel

1 rule
Detection Severity Format
Email containing malware sent by an internal sender Undefined KQL

elastic/detection-rules

1 rule
Detection Severity Format
AWS SNS Topic Message Publish by Rare User High Elastic TOML

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