Why Your Microsoft 365 Login is at Risk: New Phishing Attack Hides in Azure Blob Storage

CYBERDUDEBIVASH • ThreatWire

Published: October 19, 2025

Why Your Microsoft 365 Login is at Risk: New Phishing Attack Hides in Azure Blob Storagewww.cyberdudebivash.com•cyberdudebivash-news.blogspot.com•cyberbivash.blogspot.com•cryptobivash.code.blog

TL;DR: Criminals are spinning up Azure Blob Storage static sites (e.g., *.z*.web.core.windows.net / *.blob.core.windows.net) that host look-alike Microsoft 365 pages. These pages steal credentials and MFA codes, then pivot into your tenant. Block fast: inspect URLs beyond the “Microsoft look,” restrict unknown Azure Storage hostnames, use Safe Links/Defender detonation, enforce phishing-resistant MFA, and monitor suspicious consent/OAuth token events.

Audience: US • EU • UK • AU • IN SOC/IR teams, M365 admins, IT helpdesks, and executive risk owners.

Why this works

Trusted cloud domain halo: Many filters “allow” *.windows.net / *.azureedge.net traffic by default.
Static Website + SAS: Attackers enable static hosting and share via short-lived SAS links or custom subpaths that look corporate.
Pixel-perfect UX: Brand-accurate HTML/CSS mimics Microsoft’s login; some flows proxy live login.microsoftonline.com and steal session tokens (AiTM).
HTML smuggling: Email carries a benign HTML file that reconstructs the payload in the browser to bypass attachment scanning.

What you’ll see in the wild

Sender themes: “document share,” “payment remittance,” “DLP quarantine,” or “new Teams voicemail.”
Links like: https://<random>.z13.web.core.windows.net/<brand>/index.html or https://<name>.blob.core.windows.net/<container>/signin/.
On submit: credentials posted to attacker C2 or reverse-proxied to harvest MFA cookies (Adversary-in-the-Middle).

Immediate protections (do these now)

Turn on phishing-resistant MFA for admins and high-risk users (FIDO2 security keys / Windows Hello for Business). Avoid SMS/voice.
Microsoft Defender for Office Safe Links: rewrite & detonate links, block click-time to unknown *.web.core.windows.net/*.blob.core.windows.net when not owned by you.
Conditional Access: require compliant devices for risky sign-ins; block legacy protocols; enforce token binding / Continuous Access Evaluation.
Disable “user consent” to apps and enable admin consent workflow; verify Publisher Verification for OAuth apps.
Educate fast: teach users to expand the address bar fully—Microsoft login lives under login.microsoftonline.com or microsoft.com domains only.

Blocklist / Allowlist strategy for Azure Storage

Allowlist only your storage hostnames (e.g., myorg.blob.core.windows.net, myorg.z13.web.core.windows.net); default-deny all others at proxy/SWG.
Inspect referrers & destinations for web.core.windows.net and blob.core.windows.net accessed directly from email clicks.
Use TLS inspection on egress where permitted to extract full host & path for policy decisions.

Detection ideas (SOC playbook)

KQL – unusual Azure Storage hosts clicked from email

EmailEvents
| where Timestamp > ago(14d)
| where ThreatTypes has_any ("phish","credentialPhish","url")
| join kind=leftouter UrlClickEvents on NetworkMessageId
| where Url has_any ("web.core.windows.net","blob.core.windows.net")
| summarize clicks=count(), users=dcount(AccountUpn) by UrlDomain, bin(Timestamp, 1d)
| order by clicks desc

KQL – consent grant anomalies

AuditLogs
| where OperationName == "Consent to application"
| where ResultDescription !~ "Admin consented"
| summarize grants=count(), users=dcount(InitiatedBy.user.userPrincipalName) by TargetResources[0].displayName, bin(TimeGenerated, 1d)

Hunt: bursts of sign-ins from fresh IPs / impossible travel right after a click to suspicious Azure Storage hosts; Sign-in logs with non-compliant device + unfamiliar token key IDs.

Helpdesk response (when a user reports a page)

Collect the full URL and browser HAR if possible; disable the user account temporarily and revoke refresh tokens.
Reset password and enforce step-up MFA re-registration; inspect mailbox rules and OAuth grants.
Search tenant for other clicks to the same hostname; purge the original email via Threat Explorer.

User coaching (60-second rule)

Always check the domain in the address bar. If it’s not login.microsoftonline.com, do not type your password.
Never approve MFA prompts you did not initiate. Prefer number matching or FIDO2 keys.
Report suspicious pages using your company’s “Report Phish” add-in or forward to the SOC address.

Explore more on ThreatWire:

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Microsoft 365 phishing, Azure Blob Storage static website, web.core.windows.net, blob.core.windows.net, adversary-in-the-middle, MFA token theft, Safe Links policy, Conditional Access, OAuth consent phishing, app governance, M365 Defender, KQL hunting, enterprise email security, US EU UK AU India.

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Educational analysis. Implement changes in a test cohort before broad rollout; validate impact with staged phishing simulations and egress policy checks.

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