Malicious Office 365 Email Rule Breach - On Behalf (via office365)
- Product
- azure
- Service
- office365
- Author
- HuntRule
- Published
- 2026-08-20
- Updated
- 2026-08-28
ATT&CK techniques
Initial Access → CollectionRecon
Resource Dev
Initial Access
Execution
Persistence
Priv Esc
Defense Evasion
Cred Access
Discovery
Lateral Movement
Collection
C2
Exfiltration
Impact
What it detects
This rule detects attempt to hide emails in order to perform phishing attacks by replacing, for example, financial information from the original email with another email containing attacker's financial information. This technique may also be used to avoid specific email notification to be received by end users in case, for example, of an ongoing breach.
Reporting behind it
- attack.mitre.orghttps://attack.mitre.org/techniques/T1114/
- attack.mitre.orghttps://attack.mitre.org/techniques/T1566/
- redcanary.comhttps://redcanary.com/blog/email-forwarding-rules/
- raw.githubusercontent.comhttps://raw.githubusercontent.com/PwC-IR/Business-Email-Compromise-Guide/main/PwC-Business_Email_Compromise-Guide.pdf
- docs.microsoft.comhttps://docs.microsoft.com/en-us/microsoft-365/security/defender/alert-grading-playbook-email-forwarding?view=o365-worldwide
- logrhythm.comhttps://logrhythm.com/blog/detecting-and-preventing-auto-forwarding-and-phishing-attacks-in-office-365/
- huntress.comhttps://www.huntress.com/blog/business-email-compromise-via-azure-administrative-privileges
Detection content is published as a reviewed draft. Tune thresholds and exclusions against your own telemetry before enabling this rule for alerting.
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