CVE-2021-22905 in App
Summary
by MITRE • 06/11/2021
Nextcloud Android App (com.nextcloud.client) before v3.16.0 is vulnerable to information disclosure due to searches for sharees being performed by default on the lookup server instead of only using the local Nextcloud server unless a global search has been explicitly chosen by the user.
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Analysis
by VulDB Data Team • 06/14/2021
The vulnerability identified as CVE-2021-22905 affects the Nextcloud Android client application version 3.16.0 and earlier, representing a significant information disclosure risk that violates fundamental security principles of data privacy and user confidentiality. This flaw stems from the application's default behavior of performing sharee lookups against external lookup servers rather than restricting searches to local Nextcloud infrastructure, creating an unintended data exfiltration channel that exposes user information to third-party services without explicit user consent or awareness.
The technical implementation flaw resides in the application's default search configuration where the Nextcloud Android client automatically routes sharee discovery requests through external lookup servers instead of utilizing only the local Nextcloud instance's capabilities. This design decision creates a scenario where user account information, contact details, and sharing-related metadata are transmitted to external servers during normal operation. The vulnerability specifically impacts the sharing functionality of Nextcloud, where users attempt to invite others to access files or folders through the application's interface. When users search for recipients to share content with, the application's default behavior sends these search queries to lookup servers, potentially exposing sensitive information about user identities and sharing preferences to entities outside the organization's control.
The operational impact of this vulnerability extends beyond simple information leakage to encompass potential privacy violations and compliance issues within enterprise environments. Organizations relying on Nextcloud for secure file sharing and collaboration may inadvertently expose their user base information to external parties through this default configuration. The vulnerability particularly affects scenarios where organizations implement strict data governance policies and require all user data to remain within their controlled infrastructure. Attackers could potentially leverage this vulnerability to gather intelligence about user populations, identify active users, and map sharing relationships within organizations, creating opportunities for targeted social engineering attacks or further exploitation attempts.
The security implications of this vulnerability align with CWE-200, which addresses "Information Exposure," and can be categorized under the ATT&CK technique T1041, "Exfiltration Over C2 Channel," as the vulnerability enables data exfiltration through unintended communication channels. This flaw represents a violation of the principle of least privilege and data minimization, as the application collects and transmits more information than necessary for its core functionality. Organizations using Nextcloud may find themselves in violation of privacy regulations such as GDPR, CCPA, and other data protection frameworks that require explicit consent for data processing activities and mandate that personal information be handled within defined boundaries.
The recommended mitigation strategy involves upgrading to Nextcloud Android client version 3.16.0 or later, which addresses this vulnerability by implementing proper local-only search behavior as the default configuration. Organizations should also conduct security reviews of their Nextcloud deployment to ensure that all client applications are updated to the latest versions and that appropriate network segmentation controls are in place to prevent unauthorized communication with external lookup servers. Additionally, administrators should implement monitoring solutions to detect unusual network traffic patterns that might indicate unauthorized data exfiltration attempts, and establish clear policies regarding the use of external lookup services within their organization's security framework.