Can You Trust That Shared File? How to Spot Fake Cloud Invitations
/Article summary: Cybercriminals exploit legitimate file-sharing services like OneDrive, SharePoint, Dropbox, and Google Drive to distribute convincing phishing attacks. Because notifications may come from trusted platforms or compromised vendor accounts, these scams can be difficult to detect. Verifying unexpected file invitations, using phishing-resistant MFA, and strengthening sharing controls can help businesses protect their accounts and prevent financial fraud.
It's Tuesday afternoon when an email arrives from a longtime vendor. The subject line reads, “Q3 Audit Documents shared with you.” It comes from their legitimate email address, displays the familiar OneDrive logo, and links to a genuine Microsoft page.
You click the link and are prompted to verify your email address with a code. Then you're asked to sign in to access the document.
That's where things get suspicious.
Modern phishing attacks don't always rely on fake websites or obviously fraudulent emails. Cybercriminals increasingly exploit legitimate cloud-sharing tools to make malicious requests appear trustworthy, making these scams harder to recognize.
Why Fake Cloud Invitations Fool Smart People
Checking sender addresses and hovering over links are still useful precautions. But they aren't always enough to catch modern phishing attacks.
According to Microsoft Threat Intelligence, attackers have increasingly used legitimate file-sharing services, including OneDrive, SharePoint, and Dropbox, to evade security defenses.
One common tactic starts with a compromised vendor account. Criminals upload a malicious document, restrict access to specific recipients, and share it through the cloud platform.
The recipient receives a legitimate sharing notification, sometimes appearing to come directly from a trusted vendor. Because the file is hosted on a familiar service, the invitation may appear harmless. However, the document can contain a link leading to a phishing page designed to steal login credentials.
Google has documented similar attacks involving Google Drive. Its automatic sharing notifications can also carry malicious links, making fraudulent invitations appear more credible.
The danger isn't necessarily the sharing notification itself. It's the malicious content hiding behind a legitimate service.
What Happens After You Click?
A malicious cloud-sharing invitation may lead you through several steps before exposing your account:
The document opens. A shared file with a title like "Payment Remittance" or "Password Reset Required" appears on a legitimate cloud platform.
You're directed elsewhere. A button labeled "View Full Document" takes you to a convincing Microsoft 365 or Google sign-in page.
You enter your credentials. The fraudulent page captures your password and may prompt you to complete multifactor authentication (MFA).
The attacker gains access. In more sophisticated attacks, criminals intercept your authenticated session, potentially allowing them to access your account without completing MFA again.
This technique, known as adversary-in-the-middle (AiTM) phishing, exploits session tokens that keep users signed in. According to Microsoft's security research, stolen authentication tokens can allow attackers to bypass certain MFA protections.
Once inside a compromised mailbox, criminals may monitor conversations, identify upcoming payments, and impersonate trusted contacts to redirect funds. This is a common form of business email compromise (BEC).
The financial damage can be substantial. The FBI's 2025 Internet Crime Report recorded 24,768 BEC complaints and more than $3 billion in reported losses.
How to Spot a Fake Shared Document
You Weren't Expecting It
Did a vendor suddenly share an invoice or contract nobody discussed? Before opening it, confirm the request through a trusted contact method.
The Federal Trade Commission recommends using a phone number or website you already know is legitimate, not the contact information in the suspicious message.
It Redirects You to an Unexpected Login Page
Legitimate cloud services sometimes require additional verification. However, a document that sends you to an unfamiliar sign-in page should raise concerns. Don't enter your credentials until you've verified the request and website.
The Title Creates Pressure
"Action Required." "Account Suspended." "Final Notice." Scammers use urgency to push people into acting without thinking. Be especially cautious when an unexpected document demands immediate action.
Something Doesn't Add Up
A generic greeting, unusual wording, or a request that doesn't match your contact's normal behavior can signal trouble. Even messages from familiar accounts deserve scrutiny. When in doubt, contact the sender directly using a trusted phone number.
Building a Team That Pauses Before It Clicks
Recognizing phishing attempts takes more than occasional security reminders. Build these practices into your team's daily routine:
Normalize verification. Encourage employees to call vendors using trusted contact information when unexpected files arrive.
Use phishing-resistant MFA. Passkeys and FIDO2 security keys provide stronger protection against credential theft than traditional verification codes. Our guide to secure authentication explains the options.
Review external-sharing permissions. Configure Microsoft 365 and Google Workspace sharing controls to limit unnecessary access and reduce exposure to suspicious content.
Make reporting easy. Employees should know how to report suspicious sharing invitations so IT can investigate and warn others.
Respond quickly to compromised accounts. If someone enters credentials on a phishing page, reset their password, revoke active sessions, and investigate suspicious activity. Stolen session tokens may remain usable after a password change.
These precautions matter because attackers increasingly exploit trusted business relationships. A compromised vendor account can make a malicious file invitation appear legitimate.
As we explored in our article about a SharePoint phishing scam targeting Office 365 credentials, the delivery methods may change, but the objective remains the same: gaining unauthorized access to your accounts and information.
Would Your Team Catch a Fake Share?
File-sharing phishing exploits the trust employees place in familiar platforms and business contacts. Verifying unexpected requests, using phishing-resistant MFA, and reviewing sharing permissions can significantly reduce your company's exposure.
Since 2003, BrainStomp has helped Indiana businesses strengthen their IT security. Our team can review your Microsoft 365 or Google Workspace settings, identify potential vulnerabilities, and help employees recognize suspicious sharing invitations.
Call BrainStomp at 260-918-3548 or contact us online to discuss your security needs.
Article FAQs
How can I tell if a shared OneDrive or Google Drive file is fake?
Be cautious of unexpected files, unfamiliar login pages, or requests to enter credentials after opening a document. Legitimate sharing services may require verification, so confirm suspicious invitations directly with the sender using trusted contact information.
Can a phishing email come from a real vendor's address?
Yes. Attackers can compromise a vendor's account and use legitimate cloud-sharing services to distribute malicious files. The invitation may come from a genuine account even though the request is fraudulent.
Does MFA stop file sharing phishing?
MFA provides important protection, but some sophisticated attacks can steal authenticated session tokens and bypass certain MFA methods. Phishing-resistant options, such as passkeys and FIDO2 security keys, offer stronger protection against these techniques.