Description
WordPress is prone to a cross-domain Flash injection vulnerability. An attacker may leverage this issue to execute arbitrary script code in the browser of an unsuspecting user in the context of the affected site, allowing the attacker to steal cookie-based authentication credentials, or to fool a user into inserting credentials on a fake Flash form. WordPress versions 4.8.x ranging from 4.8 and up to (and including) 4.8.4 are vulnerable.
Remediation
Update to WordPress version 4.8.5 or latest
References
https://opnsec.com/2017/10/cve-2016-9263-unpatched-xsf-vulnerability-in-wordpress/
https://opnsec.com/2017/10/flashme-wordpress-vulnerability-disclosure-cve-2016-9263/
Related Vulnerabilities
WordPress Plugin WP Custom Pages 'url' Parameter Local File Disclosure (0.5.0.1)
WordPress Plugin Forums 'url' Parameter Arbitrary File Disclosure (1.4.3)
Atlassian Jira URL Redirection to Untrusted Site ('Open Redirect') Vulnerability (CVE-2019-20901)
WordPress Plugin Slimstat Analytics Cross-Site Scripting (0.9.2)