CVE-2020-12851 in Cells
Summary
by MITRE
Pydio Cells 2.0.4 allows an authenticated user to write or overwrite existing files in another user’s personal and cells folders (repositories) by uploading a custom generated ZIP file and leveraging the file extraction feature present in the web application. The extracted files will be placed in the targeted user folders.
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Analysis
by VulDB Data Team • 06/05/2020
This vulnerability exists in Pydio Cells 2.0.4, a collaborative file sharing platform that allows users to manage and share files within a web-based interface. The flaw represents a critical privilege escalation and lateral movement opportunity within the application's file handling mechanisms. An authenticated user can exploit this weakness by crafting a specially designed ZIP file that, when uploaded and processed by the web application, will extract its contents into arbitrary directories within the target user's personal or cells folders. This behavior fundamentally undermines the application's access control model and user isolation principles, allowing one user to directly manipulate another user's file storage space without proper authorization.
The technical implementation of this vulnerability stems from improper input validation and inadequate path traversal controls within the file extraction functionality. When the application processes uploaded ZIP archives, it fails to properly sanitize or validate the file paths contained within the archive, enabling attackers to specify absolute or relative paths that point to locations outside the intended extraction directory. This weakness falls under CWE-22, which specifically addresses path traversal vulnerabilities, and more broadly aligns with CWE-73, concerning improper neutralization of special elements used in file names. The vulnerability operates at the application layer and directly impacts the integrity and confidentiality of user data by enabling unauthorized file modification or creation.
The operational impact of this vulnerability is significant as it allows for persistent unauthorized access to user data and potential data exfiltration or corruption. An attacker could overwrite critical files, inject malicious content into user repositories, or create backdoor files that would persist even after the initial exploit. The vulnerability also enables a form of privilege escalation where a regular authenticated user can gain access to another user's personal data and repositories, effectively bypassing the application's built-in user isolation mechanisms. This type of vulnerability is particularly concerning in enterprise environments where multiple users share a single file sharing platform, as it could facilitate data breaches or insider threat scenarios. The attack vector is relatively simple to execute, requiring only the ability to upload files and access the file extraction functionality, making it a high-risk vulnerability that could be exploited by both internal and external threat actors.
Mitigation strategies should focus on implementing robust input validation and path sanitization within the file extraction process. The application should enforce strict directory boundaries during ZIP file processing, ensuring that extracted files are confined to the intended target directories. Implementing proper access control checks before file extraction operations and validating all file paths against a whitelist of allowed directories would significantly reduce the attack surface. Additionally, the application should log all file upload and extraction activities for audit purposes. From an ATT&CK perspective, this vulnerability maps to technique T1078.004, which covers valid accounts with restricted permissions being used to access systems or data, and T1566.001, involving the exploitation of vulnerabilities in remote services through malicious file uploads. Organizations should also consider implementing network segmentation and monitoring for unusual file upload patterns to detect potential exploitation attempts. Regular security updates and patch management are essential to address this vulnerability and prevent similar issues in future versions of the software.