php - XSS, encoding a return url -

here vulnerable code

  <?php header("location: ".$_post['target']); ?> 

what appropriate way make sure nasty things come in target cleaned?

first up, vulnerability

owasp categorizes "unvalidated redirects , forwards". see owasp's guide more information.

a few interesting attacks possible. see this thread on sla.ckers.org ideas on how can abused.

how protect yourself?

• verify scheme of url. want support http , https. abort request other scheme.
• parse url, , extract domain. allow redirects known list of domains. other domains, abort request.

that's it.