In wp-includes/formatting.php in WordPress 3.7 to 5.3.0, the function wp_targeted_link_rel() can be used in a particular way to result in a stored cross-site scripting (XSS) vulnerability. This has been patched in WordPress 5.3.1, along with all the previous WordPress versions from 3.7 to 5.3 via a minor release.
https://www.debian.org/security/2020/dsa-4677
https://www.debian.org/security/2020/dsa-4599
https://wpvulndb.com/vulnerabilities/9975
https://wordpress.org/news/2019/12/wordpress-5-3-1-security-and-maintenance-release/
https://seclists.org/bugtraq/2020/Jan/8
https://hackerone.com/reports/509930
https://github.com/WordPress/wordpress-develop/security/advisories/GHSA-xvg2-m2f4-83m7
https://github.com/WordPress/wordpress-develop/commit/1f7f3f1f59567e2504f0fbebd51ccf004b3ccb1d