CVE-2025-27553 in Commons VFS
Summary
by MITRE • 03/23/2025
Relative Path Traversal vulnerability in Apache Commons VFS before 2.10.0.
The FileObject API in Commons VFS has a 'resolveFile' method that takes a 'scope' parameter. Specifying 'NameScope.DESCENDENT' promises that "an exception is thrown if the resolved file is not a descendent of the base file". However, when the path contains encoded ".." characters (for example, "%2E%2E/bar.txt"), it might return file objects that are not a descendent of the base file, without throwing an exception. This issue affects Apache Commons VFS: before 2.10.0.
Users are recommended to upgrade to version 2.10.0, which fixes the issue.
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Analysis
by VulDB Data Team • 03/27/2025
The vulnerability described in CVE-2025-27553 represents a critical relative path traversal flaw within Apache Commons Virtual File System library version 2.9.0 and earlier. This issue specifically targets the FileObject API's resolveFile method which is designed to enforce file system security boundaries through the NameScope.DESCENDENT parameter. The intended security mechanism fails when encountering encoded path traversal sequences, creating a potential exploitation vector that allows attackers to bypass directory restrictions and access files outside the designated base directory scope. The vulnerability exists in the core file resolution logic where the system incorrectly processes percent-encoded ".." sequences as valid path components rather than recognizing them as traversal attempts. This flaw directly impacts applications that rely on Commons VFS for secure file operations and demonstrates a fundamental breakdown in path validation mechanisms that should prevent unauthorized access to file system resources. The issue is particularly concerning because it operates at the API level where security boundaries are expected to be enforced, making it a significant concern for enterprise applications that depend on proper file system isolation.
The technical implementation of this vulnerability stems from the improper handling of URL-encoded path traversal sequences within the resolveFile method. When developers specify NameScope.DESCENDENT, the system should enforce that all resolved file paths remain within the base file's directory hierarchy. However, the vulnerability occurs because the implementation fails to properly decode and validate encoded ".." sequences such as "%2E%2E/bar.txt" before performing the descendant check. This creates a scenario where encoded traversal characters are treated as legitimate path components rather than malicious input, allowing the method to return file objects that exist outside the originally specified base directory. The flaw essentially bypasses the security boundary enforcement mechanism by treating encoded path components as literal path elements rather than recognizing them as traversal attempts that should trigger the exception mechanism. This type of vulnerability is classified as a path traversal attack pattern and aligns with CWE-22 (Improper Limitation of a Pathname to a Restricted Directory) and CWE-77 (Improper Neutralization of Special Elements used in a Command). The vulnerability represents a classic case of insufficient input validation where encoded sequences are not properly normalized before security checks are applied.
The operational impact of CVE-2025-27553 extends beyond simple file access violations to potentially enable broader system compromise scenarios. Applications utilizing Commons VFS with the affected versions may become vulnerable to unauthorized file reading, writing, or deletion operations that could expose sensitive data or allow attackers to manipulate system files. The vulnerability is particularly dangerous in web applications where user-supplied paths might be processed through the affected API, potentially enabling attackers to traverse file system boundaries and access configuration files, database files, or other sensitive resources. Security controls that depend on the NameScope.DESCENDENT parameter for enforcing directory isolation become ineffective, creating potential data leakage scenarios. The impact is amplified in environments where Commons VFS is used for file upload handling, content management, or any scenario requiring strict file system access controls. From an attacker's perspective, this vulnerability provides a straightforward path traversal method that does not require complex exploitation techniques, making it particularly attractive for automated attacks. The vulnerability also affects systems that implement security policies based on file system boundaries, potentially undermining the entire security model of applications that depend on Commons VFS for secure file operations.
Organizations affected by this vulnerability should prioritize immediate upgrade to Apache Commons VFS version 2.10.0 or later, which contains the necessary patches to address the path traversal handling. The fix implemented in version 2.10.0 properly handles encoded traversal sequences by ensuring that percent-encoded ".." characters are decoded and validated before the descendant check is performed. Security teams should conduct comprehensive vulnerability assessments to identify all applications that utilize the affected Commons VFS versions and ensure proper patching across the enterprise environment. Additionally, organizations should review their file system access patterns and implement additional defensive measures such as input sanitization, path normalization, and access control monitoring. The vulnerability highlights the importance of proper encoding handling in security-critical APIs and serves as a reminder that URL encoding can be used as a bypass mechanism for path validation controls. From a compliance perspective, this vulnerability may impact organizations subject to data protection regulations that require proper file system access controls and data isolation. System administrators should also monitor for any unusual file access patterns that might indicate exploitation attempts and consider implementing additional logging and alerting mechanisms around file system operations that utilize the affected API. The vulnerability demonstrates the critical need for thorough testing of security controls, particularly those involving path resolution and access boundary enforcement, to ensure that encoded input sequences are properly handled and validated.