CVE-2022-29243 is a vulnerability affecting Nextcloud Server, a widely used self-hosted productivity and file sharing platform. The issue arises from improper input validation (CWE-20) related to the handling of new session names when creating app passwords. Specifically, in Nextcloud versions prior to 22.2.7 and between 23.0.0 and 23.0.4, there is no limit on the size of the input for session names. This allows users to create app passwords with excessively long names. When these long session names are subsequently loaded into memory during usage, they cause uncontrolled resource consumption (CWE-400), leading to degraded server performance. This can manifest as increased memory usage and potential denial of service conditions due to resource exhaustion. The vulnerability does not require elevated privileges beyond user-level access to create app passwords, and no user interaction beyond the creation of such passwords is needed. The flaw was addressed in Nextcloud versions 22.2.7 and 23.0.4 by implementing proper input size validation to restrict the length of session names. Currently, there are no known workarounds for this vulnerability, and no exploits have been reported in the wild. The vulnerability primarily impacts the availability and performance of Nextcloud servers rather than confidentiality or integrity.

For European organizations relying on Nextcloud Server for file sharing and collaboration, this vulnerability poses a risk of degraded service availability and performance. An attacker with user-level access could exploit this flaw to create app passwords with very long session names, causing excessive memory consumption and potentially leading to denial of service conditions. This could disrupt business operations, especially for organizations with high dependency on Nextcloud for daily workflows. While the vulnerability does not directly compromise data confidentiality or integrity, the availability impact could indirectly affect productivity and cause operational delays. Organizations in sectors such as government, finance, healthcare, and critical infrastructure that use Nextcloud for sensitive or essential services may experience significant disruption. Additionally, since Nextcloud is often self-hosted, organizations with limited IT resources might find it challenging to detect and mitigate the performance degradation caused by this issue without applying the patch.

1. Immediate upgrade of Nextcloud Server instances to version 22.2.7 or 23.0.4 or later is the most effective mitigation to address this vulnerability. 2. Implement monitoring of server resource usage, particularly memory consumption related to app password sessions, to detect abnormal spikes that may indicate exploitation attempts. 3. Restrict user permissions to create app passwords where possible, limiting this capability to trusted users or administrators to reduce the attack surface. 4. Conduct regular audits of app passwords and session names to identify unusually long or suspicious entries that could indicate exploitation. 5. Employ rate limiting or throttling on API endpoints or interfaces used to create app passwords to prevent abuse through automated or bulk creation of long session names. 6. For organizations unable to immediately upgrade, consider isolating Nextcloud servers behind network controls and limiting access to trusted networks to reduce exposure. 7. Maintain up-to-date backups and incident response plans to quickly recover from potential denial of service incidents caused by this vulnerability.