CVE-2019-5449 in Nextcloud Server
Summary
by MITRE
A missing check in the Nextcloud Server prior to version 15.0.1 causes leaking of calendar event names when adding or modifying confidential or private events.
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Analysis
by VulDB Data Team • 11/14/2023
The vulnerability identified as CVE-2019-5449 represents a critical access control flaw in Nextcloud Server versions prior to 15.0.1 that compromises the confidentiality of calendar data. This issue specifically affects the calendar synchronization functionality where users can create, modify, or add calendar events with varying levels of sensitivity including confidential and private classifications. The vulnerability stems from inadequate validation mechanisms that fail to properly enforce access restrictions when processing calendar event operations.
The technical flaw manifests in the server-side processing of calendar event modifications and additions where the system does not adequately verify that users have appropriate permissions to access or modify events marked as confidential or private. This missing validation occurs during the event creation and update processes, allowing unauthorized users to potentially access calendar event names and associated metadata that should remain restricted. The vulnerability operates at the application layer and affects the calendar synchronization protocols used by Nextcloud clients including mobile applications and web interfaces. According to CWE classification, this vulnerability maps to CWE-284 Access Control Issues, specifically representing insufficient access control mechanisms that permit unauthorized access to protected resources.
The operational impact of this vulnerability extends beyond simple data exposure as it fundamentally undermines the trust model that Nextcloud establishes for users managing sensitive information in their calendar systems. Attackers could exploit this weakness to gain unauthorized access to private calendar event names, potentially leading to social engineering attacks, privacy violations, or corporate espionage. The vulnerability is particularly concerning in enterprise environments where Nextcloud serves as a collaborative platform for organizations managing sensitive business information. Organizations using older Nextcloud versions face significant risk of unauthorized data disclosure, especially when calendar events contain personal information, business strategies, or confidential meeting details. This vulnerability directly impacts the principle of least privilege and confidentiality that security-conscious organizations rely upon.
Mitigation strategies for CVE-2019-5449 require immediate system administrators to upgrade to Nextcloud Server version 15.0.1 or later where the access control checks have been properly implemented. Organizations should also conduct comprehensive audits of their calendar data to identify any potential unauthorized access that may have occurred during the vulnerable period. Additional protective measures include implementing network-level access controls, monitoring calendar access logs for suspicious activities, and ensuring that all Nextcloud components are regularly updated to maintain security posture. The ATT&CK framework categorizes this vulnerability under privilege escalation and credential access techniques where adversaries can leverage missing access controls to obtain unauthorized information. Security teams should also consider implementing data loss prevention measures specifically targeting calendar data and establish regular security assessments to identify similar access control weaknesses in other applications and services within their infrastructure.