XSS vulnerability in CVS show_subdir_lastmod support

ViewVC before versions 1.1.28 and 1.2.1 has a XSS vulnerability in CVS show_subdir_lastmod support. The impact of this vulnerability is mitigated by the need for an attacker to have commit privileges to a CVS repository exposed by an otherwise trusted ViewVC instance that also has the `show_subdir_lastmod` feature enabled. The attack vector involves files with unsafe names (names that, when embedded into an HTML stream, would cause the browser to run unwanted code), which themselves can be challenging to create. This vulnerability is patched in versions 1.2.1 and 1.1.28.