Tomcat is the Apache Jakarta Project's official implementation of Java Servlets and Java Server Pages.
Tomcat allows special characters like slash, backslash or URL-encoded backslash as a separator, while Apache does not.
A remote attacker could send a specially crafted URL to the vulnerable Tomcat server, possibly resulting in a directory traversal and read access to arbitrary files with the privileges of the user running Tomcat. Note that this vulnerability can only be exploited when using apache proxy modules like mod_proxy, mod_rewrite or mod_jk.
There is no known workaround at this time.
All Tomcat users should upgrade to the latest version:
# emerge --sync # emerge --ask --oneshot --verbose ">=www-servers/tomcat-5.5.22"