CVE-2015-6670 in Server
Summary
by MITRE
ownCloud Server before 7.0.8, 8.0.x before 8.0.6, and 8.1.x before 8.1.1 does not properly check ownership of calendars, which allows remote authenticated users to read arbitrary calendars via the calid parameter to apps/calendar/export.php.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 04/01/2025
The vulnerability identified as CVE-2015-6670 represents a critical access control flaw within the ownCloud Server authentication and authorization framework. This issue affects multiple versions of the popular cloud storage platform, specifically targeting the calendar application component that handles calendar data management and sharing. The vulnerability stems from insufficient validation of user permissions when processing calendar identifiers, creating a path for authenticated attackers to bypass normal access controls and gain unauthorized access to calendar data belonging to other users.
The technical implementation of this vulnerability resides in the apps/calendar/export.php endpoint where the system fails to properly verify ownership or permission levels associated with calendar identifiers. When a user submits a request containing a calid parameter to this export script, the application does not adequately validate whether the requesting user has legitimate access rights to the specified calendar. This improper validation creates a privilege escalation scenario where an authenticated user can manipulate the calid parameter to reference calendars owned by other users, effectively reading calendar data that should remain private and restricted to authorized individuals only.
From an operational impact perspective, this vulnerability compromises the fundamental security principle of data isolation within the ownCloud environment. Attackers can exploit this weakness to access sensitive personal and business calendar information including meeting schedules, appointments, and potentially confidential communications. The vulnerability affects all authenticated users of the system, meaning any user with valid credentials can potentially access calendar data from other users, creating widespread privacy and security implications. Organizations relying on ownCloud for collaborative work environments face significant risks as this flaw can expose confidential scheduling information that may contain business-sensitive data or personal details.
The vulnerability maps to CWE-285, which specifically addresses improper authorization within software systems, and aligns with ATT&CK technique T1078 for valid accounts and T1566 for credential access through exploitation of application vulnerabilities. This weakness demonstrates how insufficient input validation and access control checks can create pathways for lateral movement and data exfiltration within cloud environments. The impact extends beyond simple information disclosure as calendar data often contains temporal and location-based information that can be leveraged for social engineering attacks or business intelligence gathering.
Organizations should immediately implement the vendor-provided patches for ownCloud Server versions 7.0.8, 8.0.6, and 8.1.1 to address this vulnerability. Additionally, administrators should conduct thorough audits of calendar sharing permissions and implement monitoring for unusual access patterns to calendar resources. The fix typically involves implementing proper ownership verification checks before allowing calendar data export operations, ensuring that each requested calendar identifier corresponds to a calendar that the authenticated user legitimately owns or has been granted explicit access to. Security teams should also consider implementing network-level monitoring to detect potential exploitation attempts and establish incident response procedures for handling unauthorized access to user calendar data.