CVE-2026-101051 in Cloudreve
Summary
by MITRE • 09/27/2026
Cloudreve before 4.16.1 fails to properly sanitize file paths returned by remote downloaders, allowing authenticated users to create files outside the selected destination directory. Attackers can exploit path traversal sequences in downloader metadata to write files to unexpected locations within accessible namespaces.
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Analysis
by VulDB Data Team • 09/27/2026
The vulnerability identified in Cloudreve versions prior to 4.16.1 represents a critical file system access control failure rooted in improper input validation of remote download operations. This flaw specifically affects the mechanism by which the application handles metadata provided by external downloader services or plugins when initiating asynchronous file retrieval tasks. When an authenticated user requests a file from a remote source, Cloudreve processes various attributes associated with that request to determine where and how the file should be stored on the local server infrastructure. The core technical deficiency lies in the sanitization logic applied to these metadata fields, particularly those influencing the target filename or directory path structure. Instead of strictly validating against absolute paths or sequences designed to escape the designated upload namespace, the application accepts raw input that may contain traversal characters such as double dots followed by forward slashes. This lack of rigorous normalization allows an attacker to manipulate the intended storage location during the file creation process.
From a technical perspective, this vulnerability is classified under CWE-22: Improper Limitation of a Pathname to a Restricted Directory. The exploitation vector relies on the application's failure to canonicalize or strictly validate the destination path before committing it to the filesystem operations layer. By injecting path traversal sequences into downloader metadata, an authenticated user can redirect the write operation from the intended subdirectory to arbitrary locations within the server's accessible file system hierarchy. This capability effectively bypasses the logical access controls that are supposed to isolate user data and prevent cross-user contamination or unauthorized writes. The severity of this issue is amplified by the fact that it requires only authentication, which lowers the barrier for exploitation compared to unauthenticated attacks, yet still allows significant lateral movement within the storage namespace once inside the application boundary.
The operational impact of exploiting this vulnerability extends beyond simple data corruption or loss. An attacker who successfully leverages this path traversal flaw can write files to unexpected locations that may be accessible by other users or system processes. This could lead to unauthorized access to sensitive information stored in shared directories, potential overwriting of critical application configuration files if the web server's document root is within reach, or even arbitrary code execution if the attacker can upload a malicious script into an executable directory and trigger its invocation through subsequent requests. Furthermore, this flaw undermines the integrity of multi-tenant environments where strict isolation between user data is paramount for compliance with security standards such as ISO/IEC 27001 regarding information security management systems.
In terms of threat modeling, this vulnerability aligns with MITRE ATT&CK techniques related to Command and Scripting Interpreter or File Discovery, specifically in the context of lateral movement within a compromised environment. While not directly executing commands on the operating system shell, the ability to write files outside designated boundaries facilitates persistence mechanisms or further exploitation steps that rely on file placement rather than direct execution privileges. The attack pattern involves reconnaissance followed by precise manipulation of application logic to achieve unauthorized filesystem access, which is characteristic of advanced persistent threats targeting cloud storage solutions where data confidentiality and integrity are primary concerns.
To mitigate this vulnerability, immediate action must be taken to upgrade Cloudreve to version 4.16.1 or later, as the developers have addressed these sanitization issues in subsequent releases. For environments that cannot immediately patch due to operational constraints, administrators should implement strict input validation at the network perimeter using Web Application Firewalls configured to detect and block path traversal sequences such as ../ within API endpoints related to file downloads. Additionally, enforcing least-privilege principles for the application's runtime user account can limit the damage if exploitation occurs by restricting write permissions to only the specific directories intended for uploads. Regular auditing of uploaded files and monitoring for anomalous file creation patterns outside expected paths can also aid in early detection of such exploits.