CVE-2023-28833 in Server
Summary
by MITRE • 03/30/2023
Nextcloud server is an open source home cloud implementation. In affected versions admins of a server were able to upload a logo or a favicon and to provided a file name which was not restricted and could overwrite files in the appdata directory. Administrators may have access to overwrite these files by other means but this method could be exploited by tricking an admin into uploading a maliciously named file. It is recommended that the Nextcloud Server is upgraded to 24.0.10 or 25.0.4. Users unable to upgrade should avoid ingesting logo files from untrusted sources.
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Analysis
by VulDB Data Team • 04/20/2023
The vulnerability identified as CVE-2023-28833 affects Nextcloud Server, an open source home cloud implementation that provides file synchronization and sharing capabilities for individuals and organizations. This security flaw resides in the server's handling of custom logo and favicon uploads, specifically within the administrative configuration mechanisms. The vulnerability stems from insufficient input validation and file name restrictions during the upload process, creating a potential path for arbitrary file overwrite operations within the application's data directory structure.
The technical implementation of this vulnerability allows administrators to upload custom branding elements with filenames that are not properly sanitized or restricted. When administrators upload logos or favicons through the web interface, the system accepts file names without adequate validation, potentially permitting filenames that could traverse directory structures or target critical application files. This flaw specifically impacts the appdata directory where Nextcloud stores application-specific data and configuration files. The vulnerability is classified under CWE-22 as "Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')" and aligns with ATT&CK technique T1059.001 for command and scripting interpreter execution through malicious file placement.
The operational impact of this vulnerability extends beyond simple file overwrite capabilities and represents a significant security risk for organizations relying on Nextcloud Server implementations. An attacker could potentially exploit this vulnerability by tricking an administrator into uploading a maliciously named file that overwrites critical application components, configuration files, or even executable scripts within the appdata directory. This could lead to complete system compromise, data loss, or unauthorized access to sensitive information stored within the Nextcloud environment. The vulnerability is particularly concerning because it leverages the trusted administrator role to perform malicious operations that would otherwise be restricted.
Organizations affected by this vulnerability should immediately implement the recommended upgrades to Nextcloud Server version 24.0.10 or 25.0.4, which contain patches addressing the file name validation issues. For environments where immediate upgrades are not feasible, administrators should implement strict policies restricting logo and favicon uploads from untrusted sources. Additional mitigations include implementing network-level restrictions on file upload capabilities, monitoring upload activities through logging mechanisms, and conducting regular security audits of the appdata directory contents. The vulnerability demonstrates the importance of input validation and privilege separation in web applications, particularly those handling user-provided content through administrative interfaces. Organizations should also consider implementing automated security scanning tools to detect similar path traversal vulnerabilities in their Nextcloud deployments and other web applications.