Using the Serf RA layer of Subversion for HTTPS uses the apr_fnmatch API
to handle matching wildcards in certificate Common Names and Subject
Alternate Names. However, apr_fnmatch is not designed for this purpose.
Instead it is designed to behave like common shell globbing. In particular
this means that '*' is not limited to a single label within a hostname
(i.e. it will match '.'). But even further apr_fnmatch supports '?' and
character classes (neither of which are part of the RFCs defining how
certificate validation works).
Subversion stores cached credentials by an MD5 hash based on the URL and
the authentication realm of the server the credentials are cached for.
MD5 has been shown to be subject to chosen plaintext hash collisions.
This means it may be possible to generate an authentication realm which
results in the same MD5 hash for a different URL.