CVE-2022-24888 is a medium-severity vulnerability affecting Nextcloud Server, a widely used self-hosted productivity and file sharing platform. The issue arises from improper neutralization of special characters in file and folder names, specifically leading and trailing newline (\n), carriage return (\r), tab (\t), and vertical tab (\v) characters. While the server rejects these characters if they appear in the middle of names, it allows them at the start or end, which can be exploited for injection attacks. This vulnerability is classified under CWE-74, indicating improper neutralization of special elements in output used by a downstream component, which can lead to injection flaws. The flaw exists in Nextcloud versions prior to 20.0.14.4, 21.0.8, 22.2.4, and 23.0.1. Exploiting this vulnerability could allow an attacker to craft file or folder names that include these special characters, potentially manipulating downstream components that process these names, such as logging systems, backup tools, or synchronization clients. This could lead to injection of unintended commands or data, causing data corruption, unauthorized command execution, or disruption of service. No known exploits are currently reported in the wild, and no workarounds exist aside from patching. The vulnerability was publicly disclosed on April 27, 2022, and fixed in the specified versions. Given the nature of Nextcloud as a file server and collaboration platform, this vulnerability could be leveraged in multi-user environments where attackers have some ability to upload or create files and folders, potentially escalating privileges or causing denial of service through injection attacks in downstream components that do not properly sanitize these special characters.

For European organizations, the impact of CVE-2022-24888 could be significant, especially for those relying on Nextcloud for file sharing, collaboration, and productivity. Injection vulnerabilities can compromise the integrity and availability of data by allowing attackers to manipulate file system operations or inject malicious commands into downstream processes. This could lead to data corruption, unauthorized access, or disruption of services critical for business operations. Organizations in sectors such as finance, healthcare, government, and critical infrastructure that use Nextcloud internally or offer Nextcloud-based services could face operational disruptions or data integrity issues. Additionally, since Nextcloud is often deployed on-premises or in private clouds, the vulnerability could be exploited by insiders or attackers who have gained limited access, increasing the risk of lateral movement or privilege escalation within networks. The lack of known exploits reduces immediate risk, but the presence of the vulnerability in multiple supported versions means many installations remain exposed if not updated. The injection of special characters could also interfere with logging or monitoring tools, potentially obscuring attack traces and complicating incident response.

Immediately upgrade Nextcloud Server installations to versions 20.0.14.4, 21.0.8, 22.2.4, or 23.0.1 or later, depending on the version branch in use. Implement strict input validation and sanitization on file and folder names at the application layer to reject or neutralize leading and trailing special characters such as \n, \r, \t, and \v. Audit and harden downstream components that process file and folder names (e.g., backup scripts, synchronization clients, logging systems) to ensure they safely handle special characters and are not vulnerable to injection. Monitor file creation and modification logs for unusual file or folder names containing special characters to detect potential exploitation attempts. Restrict file and folder creation permissions to trusted users and services to reduce the attack surface. Conduct regular security assessments and code reviews focusing on input handling and injection risks in custom integrations with Nextcloud. Establish incident response procedures that include checking for exploitation of this vulnerability in case of suspicious activity related to file system operations.