CVE-2022-24886 is a vulnerability identified in the Nextcloud Android application, a client for the Nextcloud self-hosted productivity platform. The issue affects versions prior to 3.19.0 and involves an unintended exposure of sensitive contact information. Specifically, if the Nextcloud app has been granted access to the device's Contacts, it does not itself request the Contacts permission explicitly. Instead, any other application on the Android device that has notification permissions can access the contacts data through Nextcloud's notification channel. This creates a privilege escalation scenario where an app with relatively low permissions (notification access) can indirectly access sensitive user contact information without requiring the Contacts permission. The vulnerability is categorized under CWE-200, which relates to the exposure of sensitive information to unauthorized actors. The flaw was addressed in Nextcloud Android app version 3.19.0, which properly restricts access to contacts data and requires explicit permission. There are no known workarounds for this vulnerability, and no public exploits have been reported in the wild as of the publication date. The vulnerability was published on April 27, 2022, and has been enriched by CISA, indicating recognition by US cybersecurity authorities. The root cause lies in the Android permission model and how Nextcloud's notification integration inadvertently exposes contacts data to other apps with notification access, bypassing the intended permission boundaries. This issue is particularly relevant for users who have granted Nextcloud access to their contacts and have other apps installed that hold notification permissions, which is a common scenario on Android devices. The vulnerability impacts confidentiality by allowing unauthorized access to personal contact information, which could be leveraged for social engineering, phishing, or further targeted attacks.

For European organizations using Nextcloud's Android client, this vulnerability poses a moderate risk to the confidentiality of sensitive contact information. Contacts often contain personally identifiable information (PII) and business-critical data such as client, partner, or employee details. Unauthorized access to this data could lead to privacy violations under GDPR, resulting in regulatory penalties and reputational damage. Additionally, exposure of contacts can facilitate spear-phishing campaigns or social engineering attacks targeting the organization or its partners. Since Nextcloud is widely used by enterprises, public sector entities, and educational institutions across Europe for secure file sharing and collaboration, the vulnerability could impact a broad user base. The fact that exploitation requires only notification permission on the device means that malicious apps could stealthily harvest contact data without raising immediate suspicion. However, the vulnerability does not directly impact data integrity or availability, limiting its scope primarily to confidentiality breaches. The absence of known exploits in the wild reduces immediate risk but does not eliminate the threat, especially as attackers could develop exploits targeting this flaw. Organizations with mobile device management (MDM) policies that allow installation of unvetted apps or have users with elevated permissions on their devices are at higher risk. The vulnerability also raises concerns for sectors with strict data protection requirements, such as healthcare, finance, and government agencies in Europe.

1. Immediate upgrade: Organizations should prioritize upgrading all Nextcloud Android clients to version 3.19.0 or later, where the vulnerability is patched. 2. Mobile application management: Implement strict MDM policies to control which applications can be installed on corporate devices, minimizing the presence of potentially malicious apps with notification permissions. 3. Permission auditing: Regularly audit app permissions on employee devices, particularly focusing on apps with notification access, and restrict or remove unnecessary permissions. 4. User awareness: Educate users about the risks of granting notification permissions to untrusted apps and the importance of updating Nextcloud promptly. 5. Network monitoring: Monitor network traffic for unusual data exfiltration patterns that could indicate unauthorized access to contacts data. 6. Application sandboxing: Where possible, use Android enterprise features or third-party solutions to sandbox apps and restrict inter-app communication channels that could be exploited. 7. Incident response readiness: Prepare to respond to potential data exposure incidents by having clear procedures for notification, investigation, and remediation in compliance with GDPR. These measures go beyond generic advice by focusing on controlling the specific vector of notification permission abuse and ensuring timely patching of the vulnerable client.