is public via http://www.ruby-lang.org/en/news/2013/02/06/rdoc-xss-cve-2013-0256/

........ quoting .........


RDoc documentation generated by rdoc bundled with ruby are vulnerable to an XSS exploit. All ruby users are recommended to update ruby to newer version which includes security-fixed RDoc. If you are publishing RDoc documentation generated by rdoc, you are recommended to apply a patch for the documentaion or re-generate it with security-fixed RDoc.
Impact

RDoc documentation generated by rdoc 2.3.0 through rdoc 3.12 and prereleases up to rdoc 4.0.0.preview2.1 are vulnerable to an XSS exploit. This exploit may lead to cookie disclosure to third parties.
Details

The exploit exists in darkfish.js which is copied from the RDoc install location to the generated documentation.

RDoc is a static documentation generation tool. Patching the library itself is insufficient to correct this exploit. Those hosting rdoc documentation will need to apply the following patch.
Solution

Please apply the following patch to rdoc documatation. If applied while ignoring whitespace, this patch will correct all affected versions:

diff --git darkfish.js darkfish.js
index 4be722f..f26fd45 100644
--- darkfish.js
+++ darkfish.js
@@ -109,13 +109,15 @@ function hookSearch() {
 function highlightTarget( anchor ) {
   console.debug( "Highlighting target '%s'.", anchor );

-  $("a[name=" + anchor + "]").each( function() {
-    if ( !$(this).parent().parent().hasClass('target-section') ) {
-      console.debug( "Wrapping the target-section" );
-      $('div.method-detail').unwrap( 'div.target-section' );
-      $(this).parent().wrap( '<div class="target-section"></div>' );
-    } else {
-      console.debug( "Already wrapped." );
+  $("a[name]").each( function() {
+    if ( $(this).attr("name") == anchor ) {
+      if ( !$(this).parent().parent().hasClass('target-section') ) {
+        console.debug( "Wrapping the target-section" );
+        $('div.method-detail').unwrap( 'div.target-section' );
+        $(this).parent().wrap( '<div class="target-section"></div>' );
+      } else {
+        console.debug( "Already wrapped." );
+      }
     }
   });
 };

And, if you are using ruby 1.9, please update ruby-1.9.3 patchlevel 385. If you are using ruby 2.0.0 rc1 or prior or ruby trunk, please update to ruby 2.0.0 rc2 or trunk revision 39102 or later. You can also update RDoc itself with rubygems to RDoc 3.12.1 or RDoc 4.0.0.rc.2.
Affected versions

    All ruby 1.9 versions prior to ruby 1.9.3 patchlevel 383
    All ruby 2.0 versions prior to ruby 2.0.0 rc2 or prior to trunk revision 39102

Credit

This exploit was discovered by Evgeny Ermakov <corwmh@gmail.com>.

This vulnerability has been assigned the CVE identifier CVE-2013-0256.