Non IE browsers don’t appear to be affected, but I haven’t tested a wide range of browsers to be sure

Requests that come through from IE do NOT appear to encode all entities in the URL string, meaning they are inserted into output content directly by SSViewer::process() when rewriting hashlinks, as it directly outputs $_SERVER[‘REQUEST_URI’]

Example IE8 request
127.0.0.1 - - [18/Jun/2014:14:13:42 +1000] “GET /site/cars/brands/toyota?one=1\”onmouseover=\”alert(‘things’);\” HTTP/1.1” 200

Example FF request
127.0.0.1 - - [18/Jun/2014:14:14:22 +1000] “GET /site/cars/brands/toyota?one=1%22onmouseover=%22alert(%27things%27);%22 HTTP/1.1” 200

This causes any hash anchor to have the JS code inserted into the page as-is.

References

• silverstripe/silverstripe-framework@604c328
• silverstripe/silverstripe-framework@bdef4fc
• https://github.com/FriendsOfPHP/security-advisories/blob/master/silverstripe/framework/SS-2014-015-1.yaml
• https://www.silverstripe.org/software/download/security-releases/ss-2014-015-ie-requests-not-properly-behaving-with-rewritehashlinks