Fix for CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')

[asadeddin]

Corgea is an AI security engineer that fixes vulnerable code.

It issued this PR to fix a vulnerability for you to review.

See the issue and fix in Corgea.

Explanation of the issue

CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.

Many file operations are intended to take place within a restricted directory. By using special elements such as ".." and "/" separators, attackers can escape outside of the restricted location to access files or directories that are elsewhere on the system. One of the most common special elements is the "../" sequence, which in most modern operating systems is interpreted as the parent directory of the current location. This is referred to as relative path traversal. Path traversal also covers the use of absolute pathnames such as "/usr/local/bin", which may also be useful in accessing unexpected files. This is referred to as absolute path traversal.
In many programming languages, the injection of a null byte (the 0 or NUL) may allow an attacker to truncate a generated filename to widen the scope of attack. For example, the product may add ".txt" to any pathname, thus limiting the attacker to text files, but a null injection may effectively remove this restriction.

Explanation of the fix

The security fix sanitizes the file path by normalizing it and removing any "../" sequences to prevent path traversal attacks.

• The fix introduces a new variable, sanitizedFilePath, which is the result of normalizing filePath using path.normalize(). This ensures that any ".." or "/" sequences are resolved to their absolute paths, eliminating potential path traversal vulnerabilities.
• The sanitizedFilePath is then further sanitized by removing any "../" sequences at the start of the path using the replace() function. This prevents any attempts to access parent directories of the current location.
• The if condition is updated to check if sanitizedFilePath starts with the restricted directory path instead of filePath. This ensures that only sanitized and safe file paths are used to send files.