CVE-2021-22912 in Nextcloud
Summary
by MITRE • 06/11/2021
Nextcloud iOS before 3.4.2 suffers from an information disclosure vulnerability when searches for sharees utilize the lookup server by default instead of only on the local Nextcloud server unless a global search has been explicitly chosen by the user.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 06/14/2021
The vulnerability described in CVE-2021-22912 represents a critical information disclosure flaw within the Nextcloud iOS application version 3.4.1 and earlier. This security weakness stems from the application's default behavior of utilizing external lookup servers for sharee searches rather than restricting these queries to the local Nextcloud server environment. The flaw creates an unintended data exposure channel where user information and sharee details can be transmitted beyond the organization's controlled infrastructure.
The technical implementation of this vulnerability involves the iOS client's search functionality for sharing contacts and users within the Nextcloud ecosystem. When users perform searches for individuals or groups to share files with, the application automatically routes these queries through external lookup servers configured by the Nextcloud instance administrator. This behavior deviates from the expected security model where local searches should remain confined to the organization's internal server environment unless explicitly configured otherwise by the user or administrator.
The operational impact of this vulnerability extends beyond simple data leakage to encompass potential privacy violations and information disclosure risks. Attackers or malicious actors with access to the external lookup servers could potentially intercept and analyze sharee search queries, gaining insights into user activities, organizational structures, and sharing patterns within the Nextcloud environment. This information could be particularly valuable for social engineering attacks or targeted reconnaissance efforts against organizations using Nextcloud services.
From a cybersecurity perspective, this vulnerability aligns with CWE-200, which addresses information exposure, and represents a deviation from secure by default principles. The issue also relates to ATT&CK technique T1082, which involves discovery of system information, as the vulnerability enables unauthorized access to user and sharing information that would otherwise remain internal to the Nextcloud deployment. The flaw essentially undermines the principle of least privilege by allowing external entities to access information that should remain within the organization's controlled environment.
Organizations utilizing Nextcloud iOS applications should immediately update to version 3.4.2 or later to remediate this vulnerability. The fix implemented by Nextcloud addresses the default search behavior by ensuring that sharee lookups remain confined to the local Nextcloud server unless explicit global search functionality has been enabled by the user or administrator. Additionally, system administrators should review their Nextcloud configuration settings to ensure that lookup server configurations are appropriately restricted and that users are properly educated about the security implications of global search functionality.
The vulnerability highlights the importance of proper input validation and secure default configurations in mobile applications, particularly those handling sensitive organizational data. It underscores the necessity for comprehensive security testing of client applications to ensure that default behaviors align with security best practices and organizational security policies. This case demonstrates how seemingly minor configuration defaults can create significant security risks when they inadvertently expose internal information to external systems without explicit user consent or configuration.