Description
WordPress Plugin MyBB Cross-Poster is prone to a cross-site scripting vulnerability because it fails to properly sanitize user-supplied input. 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. This can allow the attacker to steal cookie-based authentication credentials and launch other attacks. WordPress Plugin MyBB Cross-Poster version 1.0 is vulnerable.
Remediation
Edit the source code to ensure that input is properly sanitised or disable the plugin until a fix is available
References
https://github.com/BigTiger2020/word-press/blob/main/MyBB%20Cross-Poster.md
https://www.wordfence.com/vulnerability-advisories/#CVE-2021-39338
https://wordpress.org/plugins/mybb-cross-poster/#description