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Category:   Application (Forum/Board/Portal)  >   WordPress Vendors:
WordPress Authentication Cookie Integrity Flaw Lets Remote Users Gain Administrative Privileges
SecurityTracker Alert ID:  1019923
SecurityTracker URL:
CVE Reference:   CVE-2008-1930   (Links to External Site)
Date:  Apr 25 2008
Impact:   User access via network
Fix Available:  Yes  Vendor Confirmed:  Yes  Exploit Included:  Yes  
Version(s): 2.5 only
Description:   A vulnerability was reported in WordPress. A remote user can gain elevated privileges on the target application.

Part of the authentication cookie is not included within the message authentication code calculation. As a result, a remote user can modify authentication cookies in a manner that will not be detected by the cryptographic integrity protection.

A remote user that can register a username can register a specially crafted username beginning with the string "admin" and then modify the resulting cookie to gain administrative privileges on Wordpress.

The vendor was notified on April 22, 2008.

The original advisory is available at:

Steven J. Murdoch reported this vulnerability.

Impact:   A remote user can gain administrative privileges on the target application.
Solution:   The vendor has issued a fixed version (2.5.1), available at:

Vendor URL: (Links to External Site)
Cause:   Authentication error
Underlying OS:  Linux (Any), UNIX (Any), Windows (Any)

Message History:   None.

 Source Message Contents

Subject:  [Full-disclosure] Wordpress 2.5 Cookie Integrity Protection

Wordpress 2.5 Cookie Integrity Protection Vulnerability

Original release date: 2008-04-25
Last revised: 2008-04-25
Latest version:
CVE ID: CVE-2008-1930
Source: Steven J. Murdoch <>

Systems Affected:

 Wordpress 2.5


 An attacker, who is able to register a specially crafted username on
 a Wordpress 2.5 installation, is able to generate authentication
 cookies for other chosen accounts.

 This vulnerability exists because it is possible to modify
 authentication cookies without invalidating the cryptographic
 integrity protection.

 If a Wordpress blog is configured to freely permit account creation,
 a remote attacker can gain Wordpress-administrator access and then
 elevate this to arbitrary code execution as the web server user.

 The vulnerability is fixed in Wordpress 2.5.1

I. Description

 Since version 2.5, Wordpress authenticates logged-in users through a
 cryptographically protected cookie, based on papers by Fu et al [1]
 and Liu et al [2]. This measure was introduced partly in response to
 vulnerability CVE-2007-6013 [3,4].

 The new cookies are of the form:
  "wordpress_".COOKIEHASH = USERNAME . "|" . EXPIRY_TIME . "|" . MAC 

  COOKIEHASH:  MD5 hash of the site URL (to maintain cookie uniqueness)
  USERNAME:    The username for the authenticated user
  EXPIRY_TIME: When cookie should expire, in seconds since start of epoch
  MAC:         HMAC-MD5(USERNAME . EXPIRY_TIME) under a key derived
               from a secret and USERNAME . EXPIRY_TIME.

 The flaw in this scheme is that USERNAME and EXPIRY_TIME are not
 delimited in the MAC calculation. Hence the cookie may be modified,
 without altering MAC, provided that the concatenation of USERNAME and
 EXPIRY_TIME remains unchanged.

 This class of vulnerability, the cryptographic splicing attack, was
 commented on by Fu et al [1], but Wordpress does not employ their
 recommended defence.

 An attacker wishing to exploit this vulnerability would therefore
 create an unprivileged account with its username starting with
 "admin". The cookie returned on logging into this account can then be
 manipulated so as to be valid for the administrator account.

II. Impact

 A remote attacker, who can create an account with specially crafted
 username, is able to gain administrator level access to the Wordpress
 installation. Through standard techniques, this can be escalated to
 arbitrary PHP code execution as the web server system user.

III. Solution

 Upgrade to Wordpress 2.5.1


 - De-select "Anyone can register" in the Membership section of
   General Settings to disable account creation.


  [1] Dos and Don'ts of Client Authentication on the Web,
      Kevin Fu, Emil Sit, Kendra Smith, Nick Feamster
  [2] A Secure Cookie Protocol,
      Alex X. Liu, Jason M. Kovacs, Chin-Tser Huang, Mohamed G. Gouda
  [3] Wordpress Cookie Authentication Vulnerability: CVE-2007-6013
      Steven J. Murdoch,


 2008-04-22: notified
             Confirmation of receipt received
 2008-04-25: Wordpress 2.5.1 released incorporating patch
             Vulnerability notice published


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