CVE-2020-28645 in ownCloud
Summary
by MITRE • 02/10/2021
Deleting users with certain names caused system files to be deleted. Risk is higher for systems which allow users to register themselves and have the data directory in the web root. This affects ownCloud/core versions < 10.6.
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Analysis
by VulDB Data Team • 02/27/2021
The vulnerability identified as CVE-2020-28645 represents a critical path traversal and arbitrary file deletion flaw within the ownCloud/core platform that fundamentally undermines system integrity and data security. This vulnerability stems from inadequate input validation and sanitization mechanisms within the user management functionality, specifically when processing user deletion requests with carefully crafted usernames that contain directory traversal sequences. The flaw allows authenticated attackers with sufficient privileges to manipulate the system's file handling routines and inadvertently trigger the deletion of critical system files, potentially leading to complete system compromise and data loss.
The technical exploitation of this vulnerability relies on the improper handling of user names during the deletion process, where the application fails to properly validate or sanitize input parameters before using them in file system operations. When a user account is deleted with a specially crafted name containing sequences such as '../' or similar path traversal patterns, the system's file handling logic interprets these sequences as legitimate directory navigation commands rather than malicious input. This misconfiguration creates a direct path to arbitrary file deletion capabilities, where the system's file operations traverse directories beyond the intended scope and delete files in unintended locations. The vulnerability specifically affects versions prior to 10.6 of the ownCloud/core platform, indicating that the developers identified and addressed this issue through enhanced input validation and proper path handling mechanisms in their subsequent releases.
Systems that are particularly vulnerable include those with self-registration capabilities where users can create their own accounts, combined with web server configurations that place the data directory within the web root accessible to remote users. This configuration creates a dangerous combination where an attacker can leverage the vulnerability not only to delete system files but potentially to execute arbitrary code or gain deeper system access through the deletion of critical components such as configuration files, database files, or executable binaries. The risk escalation is particularly severe in environments where the web server has elevated privileges and can traverse the entire file system hierarchy. According to CWE classification, this vulnerability maps to CWE-22 Path Traversal and CWE-77 Path Traversal, highlighting the fundamental flaw in input sanitization and path handling within the application's security architecture. The attack pattern aligns with ATT&CK technique T1059 Command and Scripting Interpreter, specifically focusing on the exploitation of application vulnerabilities to execute arbitrary commands through file system manipulation.
Organizations should prioritize immediate patching of all affected ownCloud/core installations to version 10.6 or later, where the vulnerability has been addressed through proper input validation and secure path handling mechanisms. The mitigation strategy must include comprehensive input sanitization of all user-provided data, particularly in user management functions, and the implementation of strict path validation that prevents directory traversal sequences from being processed as legitimate file system operations. Additionally, system administrators should review and restrict web server configurations to ensure that data directories are not placed within web-accessible paths, thereby limiting the potential impact of such vulnerabilities. Security monitoring should be enhanced to detect unusual file deletion patterns and unauthorized access attempts to system directories. The vulnerability serves as a critical reminder of the importance of proper input validation and secure coding practices in preventing path traversal attacks, particularly in applications handling user management and file system operations. Organizations should also consider implementing principle of least privilege access controls and regular security audits to identify and remediate similar vulnerabilities in their application environments.