CVE-2024-22402 is a medium-severity vulnerability affecting the Nextcloud Guests app, a utility designed to create guest users with restricted access to only files shared with them. The vulnerability arises from improper preservation of permissions (CWE-281), allowing guest users to load the first page of apps they are not authorized to access. This can lead to a permissions bypass depending on which apps are installed and accessible within the Nextcloud environment. The flaw exists in specific versions of the Guests app: versions 2.4.0 up to but not including 2.4.1, 2.5.0 up to but not including 2.5.1, and 3.0.0 up to but not including 3.0.1. The vulnerability does not require user interaction and can be exploited remotely over the network with low attack complexity, but it does require the attacker to have some level of privileges (PR:L) within the system. The impact primarily affects confidentiality and integrity, as unauthorized access to app pages could expose sensitive information or allow unauthorized actions within those apps. There are no known workarounds, and the recommended mitigation is to upgrade the Guests app to versions 2.4.1, 2.5.1, or 3.0.1, which contain the necessary fixes. No known exploits are currently reported in the wild, but the vulnerability's presence in a widely used collaboration platform makes timely patching important.

For European organizations, the impact of CVE-2024-22402 can be significant, especially for those relying on Nextcloud for file sharing and collaboration. Unauthorized access to app pages could lead to exposure of sensitive corporate or personal data, violating data protection regulations such as GDPR. This could result in legal penalties, reputational damage, and loss of trust. The integrity of shared data could also be compromised if unauthorized users manipulate app functionalities. Since Nextcloud is popular among European public sector entities, educational institutions, and enterprises valuing data sovereignty, the vulnerability could affect a broad range of organizations. The lack of known exploits reduces immediate risk, but the ease of exploitation and network accessibility mean attackers could leverage this flaw to escalate privileges or gather intelligence for further attacks.

European organizations should prioritize upgrading the Nextcloud Guests app to the fixed versions 2.4.1, 2.5.1, or 3.0.1 without delay. Beyond patching, organizations should audit their Nextcloud configurations to ensure minimal app installations and restrict guest user permissions strictly. Implementing network segmentation and access controls can limit exposure of Nextcloud instances to trusted networks only. Monitoring and logging access to Nextcloud apps should be enhanced to detect unusual access patterns indicative of exploitation attempts. Additionally, organizations should review their guest user policies and consider temporary suspension of guest access until patches are applied. Regular vulnerability scanning and integration of Nextcloud security advisories into patch management workflows will help maintain ongoing security.