There is an arbitrary resource file download vulnerability triggered by a third party library org.tuckey.web.filters.urlrewrite.UrlRewriteFilter.

The urlrewrite.xml rules file shows the pattern that will trigger a <to type="forward"> forward rule, which is the equivelant of performing dp = request.getServletContext().getRequestDispatcher(resource); dp.forward(request, response);. This construct allows a user to forward requests to any resource file on the server, such as /WEB-INF/web.xml - which could potentially contain sensitive information like usernames and passwords.

web.xml

...
    <!-- this filter is used to rewrite through the /s/* filter to add caching headers. see: urlrewrite.xml -->
    <filter>
        <filter-name>UrlRewriteFilter</filter-name>
        <filter-class>org.tuckey.web.filters.urlrewrite.UrlRewriteFilter</filter-class>
    </filter>

urlrewrite.xml

...
    <rule>
	<from>^/s/(.*)/_/([^\?]*).*</from>
        <run class="com.atlassian.plugin.servlet.ResourceDownloadUtils" method="addPublicCachingHeaders" />
        <to type="forward">/$2</to>
    </rule>
</urlrewrite>

The attached screenshot shows this issue being exploited. It's recommended addPublicCachingHeaders be implemented without the vulnerable library until a patch is available.