OpenACS

RFC 2616 requires an absolute URI in the "Location" header field. So

if someone calls "ns_returnredirect /", NaviServer transforms it on

the fly into an absolute URL by prefixing it with the location

(e.g. https://openacs.org/). NaviServer (and OpenACS) has some complex

code to compute the location value, especially when virtual servers

are involved (or for "host-node mapped" subsites in OpenACS). The

situation is further complicated when running behind a reverse proxy

and/or in a containerized environment. In such cases, the location is

computed from the "host" request header field, which must be

validated, otherwise an attacker could hijack a session and redirect

it to a spoofed site.

The situation changed 10 years ago (June 2014) with the introduction

of RFC 7231, which allows relative redirects (see

https://www.rfc-editor.org/rfc/rfc7231#section-7.1.2). Using relative

redirects greatly simplifies configuration and closes the attack

vector using the host header field. RFC 7231 has been superseded by

RFC 9110 (June 2022), which also supports relative redirects via the

"location" response header field (see

https://www.rfc-editor.org/rfc/rfc9110#field.location).

Since OpenACS prefixed always the URL with a location, when it

encounters are relative URL in a "ad_returnredirect", this change

makes use of the new feature of NaviServer 5.

Make sure to use a current version of NaviServer, where the support

was added recently.

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