The CivetWeb web library does not validate uploaded filepaths when running on an OS other than Windows, when using the built-in HTTP form-based file upload mechanism, via the mg_handle_form_request API. Web applications that use the file upload form handler, and use parts of the user-controlled filename in the output path, are susceptible to directory traversal
https://jfrog.com/blog/cve-2020-27304-rce-via-directory-traversal-in-civetweb-http-server/
https://groups.google.com/g/civetweb/c/yPBxNXdGgJQ
https://cert-portal.siemens.com/productcert/pdf/ssa-389290.pdf
https://cert-portal.siemens.com/productcert/pdf/ssa-222547.pdf