The MailPoet Newsletters (wysija-newsletters) plugin before 2.6.7 for WordPress allows remote attackers to bypass authentication and execute arbitrary PHP code by uploading a crafted theme using wp-admin/admin-post.php and accessing the theme in wp-content/uploads/wysija/themes/mailp/.

References

• https://nvd.nist.gov/vuln/detail/CVE-2014-4725
• http://blog.sucuri.net/2014/07/mailpoet-vulnerability-exploited-in-the-wild-breaking-thousands-of-wordpress-sites.html
• http://blog.sucuri.net/2014/07/malware-infection-breaking-wordpress-sites.html
• http://blog.sucuri.net/2014/07/remote-file-upload-vulnerability-on-mailpoet-wysija-newsletters.html
• http://www.openwall.com/lists/oss-security/2014/07/08/7
• https://wordpress.org/plugins/wysija-newsletters/changelog
• http://arstechnica.com/security/2014/07/mass-exploit-of-wordpress-plugin-backdoors-sites-running-joomla-magento-too