full-disclosure - WordPress 3.5.1, Denial of Service

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Message-Id: <61D7F99E-A22C-40CE-9364-57AFABA92447@vndh.net>
Date: Tue, 11 Jun 2013 10:10:24 +0200
From: Krzysztof Katowicz-Kowalewski <vnd@...h.net>
To: full-disclosure@...ts.grok.org.uk
Subject: WordPress 3.5.1, Denial of Service

Version 3.5.1 (latest) of popular blogging engine WordPress suffers from remote denial of service vulnerability. The bug exists in encryption module (class-phpass.php). The exploitation of this vulnerability is possible only when at least one post is protected by a password.

Time frames:
31.05.2013 WordPress security team has been informed about the vulnerability (no response).
07.06.2013 The vulnerability has been released to the public.

More information (including proof of concept):
https://vndh.net/note:wordpress-351-denial-service

A way out (before official WordPress update) to secure existing installations is to apply the following patch:

--- wp-includes/class-phpass.php
+++ wp-includes/class-phpass.php
@@ -120,7 +120,7 @@
			return $output;

		$count_log2 = strpos($this->itoa64, $setting[3]);
-		if ($count_log2 < 7 || $count_log2 > 30)
+		if ($count_log2 < 7 || $count_log2 > 13)
			return $output;

		$count = 1 << $count_log2;
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