Suspicious OWA Proxy User-Agent Indicating Mailbox Access

ATT&CK techniques

Initial Access → Collection

Recon
Resource Dev
Initial Access
- T1566.002Spearphishing Link
Execution
Persistence
Priv Esc
Defense Evasion
Cred Access
Discovery
Lateral Movement
Collection
- T1114Email Collection
C2
Exfiltration
Impact

What it detects

This rule detects the anomalous Outlook Web Access proxy User-Agent Client=OWA;Action=ViaProxy tied to attacker mailbox access. This behavior matches a phishing campaign against European organizations where compromised accounts were used to reach mailboxes through OWA proxying. This distinctive User-Agent signals post-compromise mailbox interaction and potential email collection.

Reporting behind it

Related detections9 linkedT1566.002 — drag to rearrange

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Possible AiTM Phishing Sign-On Evaluation Denied by Okta FastPass

Suspicious Cloudflare Workers Brand-Impersonation Phishing Domains via Proxy

Suspicious OWA Proxy User-Agent Indicating Mailbox Access

Pivot detection · T1566.002 · 9 related

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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