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A Wake-Up Call for Cloud Storage Security
A newly uncovered vulnerability in Microsoft’s OneDrive File Picker is making waves in the cybersecurity world. Discovered by Oasis Security, this flaw exposes millions of users to the risk of unauthorized data access due to the way third-party applications are granted permissions via OAuth. Instead of limiting access to only the files users select, the File Picker allows apps to request and potentially gain sweeping access to entire OneDrive accounts.
The issue has widespread implications. With popular platforms like ChatGPT, Slack, Trello, and ClickUp integrating this File Picker to simplify uploads, the problem scales rapidly across both personal and enterprise environments. Experts describe the flaw as a textbook example of over-permissioned OAuth scopes, paired with consent dialogs that fail to communicate the gravity of the access users are granting.
Millions at Risk Due to Over-Permissioned File Picker
Oasis Security’s research brings to light a glaring issue in Microsoft’s OneDrive File Picker system: the way it requests OAuth scopes grants third-party apps broad access to entire cloud storage drives. Instead of allowing apps to access only the files explicitly selected for uploading or sharing, the permissions requested enable full read and write access. This opens the door to potential misuse or exploitation.
Notably, the vulnerability affects both current and legacy versions of the File Picker. Version 7.0 requires full read/write access even during simple uploads, while older versions suffer from poor handling of sensitive OAuth tokens, often stored in insecure browser elements like localStorage or URL fragments. Although Version 8.0 offers developers externalized authentication, it still fails to narrow the scopes effectively.
In real-world scenarios, this vulnerability could have serious consequences. For example, a job applicant using a recruitment site like Phenome might inadvertently grant access to sensitive employer files if those documents are stored on a linked OneDrive account. These risks extend beyond the individual to entire organizations, especially if users unknowingly authorize apps that could compromise corporate data.
Security professionals warn users to be cautious when authorizing any third-party integration. They suggest implementing strict admin consent protocols and conditional-access policies to prevent apps from overreaching. Microsoft’s approach, in contrast to more secure models from Google and Dropbox, is seen as significantly less restrictive. Google Drive uses narrow, task-specific scopes, while Dropbox avoids OAuth for its picker altogether, limiting exposure.
Despite acknowledgment from Microsoft, no fixes or changes have yet been rolled out. In the meantime, Oasis Security recommends that developers avoid using refresh tokens, reduce scope requests, and audit existing app permissions. Users can also take proactive steps by reviewing Microsoft’s privacy settings to see which apps have access to their OneDrive data.
What Undercode Say:
This situation shines a glaring light on a much broader issue that plagues modern SaaS integrations: the careless handling of permissions and the illusion of user control. Microsoft’s OneDrive File Picker is only the latest example of a deeply entrenched problem where ease of integration trumps security best practices.
The critical mistake here is the “default to trust” model. Applications integrating with OneDrive are being granted sweeping permissions without granular control or transparency for end-users. Even though OAuth is meant to give users control over what data they share, this flaw turns that idea on its head by effectively giving apps a skeleton key to entire OneDrive accounts.
It’s not just a Microsoft issue — it’s a growing trend. SaaS ecosystems are expanding rapidly, and security is often an afterthought. OAuth misconfigurations, token persistence, and vague consent dialogs create fertile ground for exploitation. The fact that sensitive tokens were stored in localStorage or passed in URLs in earlier versions is a red flag that shows a lack of secure engineering foresight.
On the user side, there’s a false sense of safety. Most people assume that selecting a file means only that file is shared. But what’s happening behind the scenes is that many apps are granted far more access than necessary — sometimes for convenience, sometimes due to poor development practices, and sometimes because platforms like Microsoft make broad access the easiest option.
Comparatively, Google’s use of fine-grained OAuth scopes like drive.file offers a clear best practice. Dropbox’s avoidance of OAuth altogether for their picker is an even stronger move, limiting exposure by design. Microsoft’s delay in addressing this concern could erode user trust, especially among enterprises where data sensitivity is paramount.
Security teams should start auditing app integrations today, not tomorrow. Enforcing admin consent, using conditional-access policies, and disabling token refresh capabilities for non-essential apps could mitigate risks significantly. Developers must also take responsibility by limiting scopes in their applications and following the principle of least privilege.
In the long term, pressure from security researchers and the public will likely force Microsoft to revise its default permission structures. Until then, users and IT teams must stay vigilant. Convenience should never come at the cost of control, and this incident is a stark reminder that even the most widely-used platforms can have deep cracks in their foundation.
Fact Checker Results ✅
Microsoft OneDrive File Picker indeed requests broad OAuth scopes by default.
The issue has been acknowledged by Microsoft but not yet resolved.
Competitor platforms (Google, Dropbox) have implemented safer access control models. 🔒🔍🛑
Prediction 📊
Given the attention this vulnerability is receiving, Microsoft is likely to introduce a patch or update that redefines default OAuth scopes in the near future. Expect a push toward more fine-grained controls, better consent dialog transparency, and possibly even an overhaul of File Picker architecture. Meanwhile, users and organizations will increasingly shift toward more secure alternatives unless trust is quickly restored.
References:
Reported By: www.infosecurity-magazine.com
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