Critical Houston Business Alert: Microsoft OneDrive File Picker Security Flaw – How One File Upload Could Expose Your Entire OneDrive

 

The cybersecurity research community has uncovered a significant security vulnerability that highlights the ongoing challenges with OAuth implementation in cloud services. Oasis Security’s recent research into Microsoft’s OneDrive File Picker reveals how well-intentioned security mechanisms can create unexpected exposure risks for millions of users.

 

Research Summary

The Oasis Security Research Team conducted an in-depth analysis of Microsoft’s OneDrive File Picker implementation and discovered a fundamental flaw in how OAuth permissions are structured and communicated to users. Their research, published in May 2025, demonstrates how the official Microsoft tool designed to facilitate secure file sharing actually creates broader security risks than intended.

Key Research Findings

The research identified two primary security issues within the OneDrive File Picker ecosystem. First, the OAuth scope implementation requests excessive permissions that far exceed the functional requirements of the tool. When users upload a single file through the File Picker, the underlying OAuth request grants read access to the user’s entire OneDrive storage, not just the selected file.

Second, the user consent experience fails to adequately communicate the scope of access being granted. The consent prompts presented to users employ vague language that doesn’t clearly indicate the breadth of permissions being requested, leading to uninformed consent decisions.

Technical Analysis

The researchers examined multiple versions of the OneDrive File Picker and found consistent patterns of over-permissioning across implementations. Version 7.0 of the File Picker requests both read and write permissions for upload operations, while other versions request read permissions for uploads and write permissions for downloads. The latest version (8.0), used by applications like ChatGPT, delegates authentication handling to developers using Microsoft Authentication Library (MSAL), which introduces additional security risks through plain-text token storage in browser session storage.

Impact Assessment

The research team identified hundreds of affected applications, including major platforms such as ChatGPT, Slack, Trello, ClickUp, and Zoom. This indicates that millions of users may have unknowingly granted broad file access permissions to third-party applications. The researchers estimate the scope of exposure extends across personal and enterprise environments, creating potential compliance violations and data security risks.

Methodology and Disclosure

Following responsible disclosure practices, Oasis Security reported their findings to Microsoft and notified affected vendors. Microsoft acknowledged the vulnerability and indicated they may consider future improvements to align OneDrive File Picker functionality with more appropriate permission scopes. However, no specific timeline for remediation has been provided.

Industry Context

This research highlights broader challenges in OAuth implementation across cloud services. The researchers noted that similar file picker implementations from Google Drive and Dropbox do not exhibit the same over-permissioning issues, suggesting that more granular OAuth scope design is technically feasible.

Security Implications

The research demonstrates how security mechanisms designed to protect user data can inadvertently create new attack vectors when implementation doesn’t align with user expectations or functional requirements. The disconnect between user intent (sharing one file) and actual permissions granted (access to entire drive) represents a significant security design flaw that affects user privacy and enterprise data protection.

Research Recommendations

The research team provided several mitigation strategies while awaiting Microsoft’s official response. These include avoiding refresh token usage, implementing secure access token storage, and considering alternative file sharing mechanisms that don’t rely on the vulnerable OneDrive File Picker implementation.

The research also emphasizes the importance of regular OAuth permission audits and the implementation of administrative controls for enterprise environments to prevent unauthorized broad access grants.

 How CinchOps Can Help

This research underscores the complex security challenges that modern businesses face when implementing cloud services and third-party integrations. At CinchOps, we’ve seen firsthand how well-intentioned technology implementations can create unexpected security exposures, particularly for small and medium-sized businesses that may lack the internal expertise to properly assess these risks.

The OAuth vulnerability research perfectly illustrates why businesses need ongoing security expertise that goes beyond basic IT support. Understanding the implications of cloud service integrations requires deep technical knowledge and continuous monitoring of emerging security research.

Our comprehensive security services address these research-identified risks through:

• OAuth and API Security Audits – We conduct detailed reviews of your organization’s third-party application integrations, identifying excessive permissions and potential data exposure risks highlighted by this research
• Cloud Security Architecture Review – Our team evaluates your Microsoft 365 and cloud service configurations, ensuring that file sharing mechanisms align with your actual business requirements rather than accepting default broad permissions
• Security Research Integration – We monitor emerging security research and proactively assess how new vulnerabilities might affect your specific technology stack, providing immediate guidance when issues like the OneDrive File Picker flaw are discovered
• Compliance Risk Management – We help organizations understand how OAuth permission issues could impact regulatory compliance, particularly for businesses subject to HIPAA, SOX, or GDPR requirements
• Employee Security Training – Our training programs educate staff about the real-world implications of cloud service permissions, helping them make informed decisions about application authorizations
• Incident Response Planning – When security research reveals vulnerabilities in commonly used tools, we provide immediate assessment and mitigation strategies to protect your business data

The Oasis Security research demonstrates why businesses cannot rely solely on vendor security assurances or default configurations. Professional security oversight is essential for identifying and addressing these complex technical vulnerabilities before they become business-critical exposures.

Contact CinchOps to ensure your organization benefits from expert security guidance that keeps pace with evolving research and emerging threats.

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For Additional Information on this topic:
OneDrive File Picker Flaw Provides ChatGPT and Other Web Apps Full Read Access to Users’ Entire OneDrive

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