moddontdothat allows you to block update REPORT requests against certain paths in the repository. It expects the paths in the REPORT request to be absolute URLs. Serf based clients send relative URLs instead of absolute URLs in many cases. As a result these clients are not blocked as configured by moddontdothat (CVE-2013-4505).
When SVNAutoversioning is enabled via "SVNAutoversioning on", commits can be made by single HTTP requests such as MKCOL and PUT. If Subversion is built with assertions enabled any such requests that have non-canonical URLs, such as URLs with a trailing /, may trigger an assert. An assert will cause the Apache process to abort (CVE-2013-4558).