wp_get_referer() doesn't return false when the referer URL is the same as the current URL

[garyc40]

Inside wp_get_referer(), there's this conditional statement:

if ( $ref && $ref !== $_SERVER['REQUEST_URI'] )

It is there to ensure that wp_get_referer() doesn't return the same page I'm on. This is useful when redirecting because I can detect and avoid infinite redirection.

According to PHP documentation, $_SERVER['REQUEST_URI'] is only the URI on the host. As a result, the conditional statement above fails in this case:

Let's say I was redirected from ​http://example.com/sample-uri to itself (either by clicking a link or a form submission). Then:

$ref = 'http://example.com/sample-uri';
$_SERVER['REQUEST_URI'] = '/sample-uri';

So technically, the referrer is the same page, but wp_get_referer() doesn't return false as expected, because $ref !== $_SERVER['REQUEST_URI'].

A better conditional statement would be:

if ( $ref && parse_url( $ref, PHP_URL_PATH ) !== $_SERVER['REQUEST_URI'] )

Patch attached.

I'm using PHP 5.3.6, Apache 2.2.20.

[bpetty]

use get_site_url() in wp_get_referer() checks

[bpetty]

unit tests

[bpetty]

The original patch here breaks referer URLs from different query variables, and also doesn't account for URLs from the different servers, but (coincidentally) the same resource.

If we use get_site_url() in wp_get_referer() for comparison instead, it fixes this and accounts for query variables and different servers.

I've also attached unit tests for this.

[nacin]

The patch would break if WordPress was not at the root of a domain.

[bpetty]

I've refreshed the patch, and added subfolder unit tests, however, this patch does not actually fix the broken subfolder detection from the previous patch. It can at least now be confirmed by explicitly running the unit tests for this ticket.

I was hoping to avoid using anything complex like parse_url(), but it's looking like it would be necessary for properly handling subfolder installations unless someone else has a better suggestion for retrieving just the path from site_url without using parse_url() (maybe I'm not aware of such a method in WP already).

I'm punting this back out of 3.9 milestone for now.

[swissspidy]

Patch needed a refresh because wp_get_referer() now uses wp_validate_redirect() (see [25318] and #27152). 19856.2.diff​ is an updated patch accommodating for that.

[nacin]

This patch wold suggest that this condition is *never* hit. wp_get_referer() likely sometimes sees a root-relative referrer, no? That would imply we should add to this, not replace.

[swissspidy]

Replying to nacin:

This patch wold suggest that this condition is *never* hit. wp_get_referer() likely sometimes sees a root-relative referrer, no? That would imply we should add to this, not replace.

Makes sense. 19856.3.diff​ adjusts the condition and adds unit tests for this case.

[swissspidy]

Considering for commit if there are no objections. Will implement #27152 afterwards.

[swissspidy]

In 36242:

Ensure wp_get_referer() returns false when the referrer URL is the current URL.

Adds unit tests.

Fixes #19856.