High Severity

Headers: Self-sender using Microsoft CompAuth bypass with credential theft content

Description

Detects messages sent to self or invalid domains containing credential theft content that bypass Microsoft's CompAuth while failing both SPF and DMARC authentication checks.

References

No references.

Sublime Security
Created Apr 21st, 2026 • Last updated Apr 21st, 2026
Source
type.inbound
// self sender
and length(recipients.to) == 1
and length(recipients.cc) == 0
and length(recipients.bcc) == 0
and (
  sender.email.email == recipients.to[0].email.email
  or recipients.to[0].email.domain.valid == false
)
// cred theft
and any(ml.nlu_classifier(body.current_thread.text).intents,
        .name == "cred_theft" and .confidence != "low"
)
// microsoft compauth pass, but spf and dmarc fail
and any(headers.hops, any(.fields, strings.icontains(.value, 'compauth=pass')))
and not headers.auth_summary.dmarc.pass
and not headers.auth_summary.spf.pass
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