Avoid making decisions based on names of resources (e.g. files) if those resources can have alternate names.

Assume all input is malicious. Use an appropriate combination of black lists and white lists to ensure only valid, expected and appropriate input is processed by the system. For example, valid input may be in the form of an absolute pathname(s). You can also limit pathnames to exist on selected drives, have the format specified to include only separator characters (forward or backward slashes) and alphanumeric characters, and follow a naming convention such as having a maximum of 32 characters followed by a '.' and ending with specified extensions.

Canonicalize the name to match that of the file system's representation of the name. This can sometimes be achieved with an available API (e.g. in Win32 the GetFullPathName function).