visionmedia send before 0.8.4 for Node.js uses a partial comparison for verifying whether a directory is within the document root, which allows remote attackers to access restricted directories, as demonstrated using "public-restricted" under a "public" directory.
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.