pixabay-images.php in the Pixabay Images plugin before 2.4 for WordPress does not validate hostnames, which allows remote authenticated users to write to arbitrary files via an upload URL with a host other than pixabay.com.

References

• https://nvd.nist.gov/vuln/detail/CVE-2015-1376
• https://plugins.trac.wordpress.org/changeset?sfp_email=&sfph_mail=&reponame=&new=1067992%40pixabay-images%2Ftrunk%2Fpixabay-images.php&old=926633%40pixabay-images%2Ftrunk%2Fpixabay-images.php
• http://packetstormsecurity.com/files/130017/WordPress-Pixarbay-Images-2.3-XSS-Bypass-Upload-Traversal.html
• http://seclists.org/fulldisclosure/2015/Jan/75
• http://www.exploit-db.com/exploits/35846
• http://www.openwall.com/lists/oss-security/2015/01/25/5
• http://www.securityfocus.com/archive/1/534505/100/0/threaded