A Subversion client sometimes connects to URLs provided by the repository.
This happens in two primary cases: during 'checkout', 'export', 'update', and
'switch', when the tree being downloaded contains svn:externals properties;
and when using 'svnsync sync' with one URL argument.
A maliciously constructed svn+ssh:// URL would cause Subversion clients to
run an arbitrary shell command. Such a URL could be generated by a malicious
server, by a malicious user committing to a honest server (to attack another
user of that server's repositories), or by a proxy server.
The vulnerability affects all clients, including those that use file://,
http://, and plain (untunneled) svn://.
An exploit has been tested.