Attack Surface: Path Traversal
Description: Attackers manipulate file paths provided to Commons IO methods to access or modify files outside the intended directory, potentially gaining unauthorized access to sensitive data or system resources.
Commons IO Contribution: Provides numerous methods for file and directory manipulation (e.g., FileUtils.getFile, FileUtils.copyFile, FileUtils.openInputStream, FileUtils.openOutputStream, FilenameUtils.normalize) that are directly vulnerable if used with unsanitized user input. FilenameUtils.normalize is not a complete security solution.
Example: An application uses FileUtils.readFileToString("/var/www/app/uploads/" + userInput) where userInput is controlled by the attacker. If userInput is ../../etc/passwd, the application might read the system's password file.
Impact: * Disclosure of sensitive information (configuration files, source code, etc.). * Modification or deletion of critical files. * Potential for remote code execution (if the attacker can write to executable locations).
Risk Severity: Critical
Mitigation Strategies:
* Input Validation (Whitelist): Strictly validate all user-supplied input used in file paths. Use a whitelist approach, allowing only known-good characters and patterns. Reject any input containing "..", "/", "", or other potentially dangerous characters.
* Canonicalization: After any normalization (e.g., using FilenameUtils.normalize), use File.getCanonicalPath() to obtain the absolute, unambiguous path. Then, compare this canonical path to a known-good base directory to ensure it's within the allowed bounds. This is a crucial step.
* Least Privilege: Run the application with the minimum necessary file system permissions.
* Avoid User Input in Paths: If possible, avoid using user-supplied data directly in file paths. Use unique identifiers (UUIDs) instead.
Attack Surface: Symbolic Link Attacks
Description: Attackers create symbolic links (symlinks) that point to sensitive files or directories. Commons IO methods, by default, often follow these symlinks, leading to unintended operations on the linked targets.
Commons IO Contribution: Many FileUtils methods follow symlinks by default. While FileUtils.isSymlink exists for detection, developers must explicitly use it and handle the results correctly to prevent attacks. This is a direct contribution to the attack surface.
Example: An application uses FileUtils.copyFile(userUploadedFile, destination). If userUploadedFile is a symlink pointing to /etc/shadow, the application might inadvertently copy the system's shadow password file.
Impact: * Similar to path traversal: unauthorized access, modification, or deletion of files. * Potential for privilege escalation.
Risk Severity: High
Mitigation Strategies:
* Symlink Detection: Use FileUtils.isSymlink() to always detect symbolic links.
* Policy Enforcement: If symlinks are not expected, reject them. If they are expected, carefully validate the target of the symlink using canonicalization (as with path traversal) to ensure it's within the allowed bounds.
* Operating System Controls: Utilize OS-level features to restrict symlink creation or following, if available.
Attack Surface: Resource Exhaustion (DoS via Stream Handling)
Description: Attackers provide excessively large inputs (files or streams) to Commons IO methods that read entire inputs into memory, causing the application to consume excessive resources and leading to a denial-of-service.
Commons IO Contribution: Methods like IOUtils.toByteArray, FileUtils.readFileToByteArray, and IOUtils.toString directly read entire streams or files into memory, making them inherently vulnerable to this type of attack if input size isn't externally limited.
Example: An application uses FileUtils.readFileToByteArray(userUploadedFile) to read an uploaded file. An attacker uploads a multi-gigabyte file, causing the application to run out of memory.
Impact: * Application unavailability. * Potential for system instability.
Risk Severity: High
Mitigation Strategies:
* Input Size Limits: Enforce strict limits on the size of files and streams that the application will process before passing them to Commons IO methods.
* Streaming Processing: Whenever possible, process data in chunks (using IOUtils.copy with a limited buffer size) instead of loading entire files into memory using the vulnerable methods.
* Timeouts: Implement timeouts for stream operations to prevent indefinite hangs.