CVE-2017-9339 in ownCloud Server
Summary
by MITRE
A logical error in ownCloud Server before 10.0.2 caused disclosure of valid share tokens for public calendars. Thus granting an attacker potentially access to publicly shared calendars without knowing the share token.
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Analysis
by VulDB Data Team • 10/27/2019
The vulnerability identified as CVE-2017-9339 represents a significant logical flaw in ownCloud Server versions prior to 10.0.2 that compromised the security of publicly shared calendars. This issue stems from improper access control mechanisms that failed to adequately validate share token secrecy, creating a scenario where unauthorized parties could potentially gain access to calendar data without possessing the legitimate share token. The flaw specifically affected the calendar sharing functionality within the ownCloud platform, which is a critical component for collaborative work environments and personal data management systems.
The technical implementation error manifested in the server's handling of public calendar sharing operations where the system did not properly enforce the secrecy requirement for share tokens. This logical inconsistency allowed attackers to exploit the system by discovering valid share tokens through various means, effectively bypassing the intended authentication and authorization mechanisms. The vulnerability falls under the category of improper access control as defined by CWE-284, where the system fails to properly restrict access to resources based on the user's authorization level. The flaw essentially created a situation where the share token, which should have remained secret and unique to legitimate users, became discoverable by malicious actors.
The operational impact of this vulnerability extends beyond simple information disclosure, as it represents a fundamental breach in the security model of the calendar sharing feature. Organizations relying on ownCloud for collaborative work environments faced potential exposure of sensitive calendar data including meeting schedules, personal appointments, and potentially confidential business information. The vulnerability could be exploited by attackers who might discover valid share tokens through automated scanning, brute force attempts, or by analyzing the system's response patterns to sharing requests. This creates a significant risk for enterprises where calendar data might contain proprietary information, strategic planning details, or personal privacy data that should remain restricted to authorized users only.
The security implications of CVE-2017-9339 align with several ATT&CK tactics including privilege escalation and credential access, as attackers could potentially gain unauthorized access to calendar resources without proper authentication. The vulnerability demonstrates how seemingly minor logical errors in access control implementations can create substantial security risks, particularly in collaborative platforms where sharing mechanisms are fundamental to the system's functionality. Organizations using vulnerable versions of ownCloud needed to implement immediate mitigations including upgrading to version 10.0.2 or later, which addressed the share token handling logic. Additionally, administrators should review existing calendar shares to revoke access for potentially compromised tokens and implement monitoring for unusual sharing activity.
The remediation approach for this vulnerability required a complete overhaul of the calendar sharing validation logic within the ownCloud server implementation. Version 10.0.2 introduced proper token generation and validation mechanisms that ensured share tokens remained secret and were properly validated against the system's access control policies. This fix aligns with security best practices for implementing secure sharing mechanisms and demonstrates the importance of thorough testing of access control logic in collaborative software platforms. The vulnerability serves as a reminder of the critical importance of proper access control implementation in web applications, particularly those handling user data and collaborative features where the security of sharing mechanisms directly impacts overall system security posture.