XZ Utils provide a general-purpose data-compression library plus command-line tools. When built for native Windows (MinGW-w64 or MSVC), the command line tools from XZ Utils 5.6.2 and older have a command line argument injection vulnerability. If a command line contains Unicode characters (for example, filenames) that don't exist in the current legacy code page, the characters are converted to similar-looking characters with best-fit mapping. Some best-fit mappings result in ASCII characters that change the meaning of the command line, which can be exploited with malicious filenames to do argument injection or directory traversal attacks. This vulnerability is fixed in 5.6.3. Command line tools built for Cygwin or MSYS2 are unaffected. liblzma is unaffected.