XSS exists in the the-holiday-calendar plugin before 1.11.3 for WordPress via the thc-month parameter.
https://wordpress.org/plugins/the-holiday-calendar/#developers
https://seclists.org/fulldisclosure/2015/Jul/125
Source: Mitre, NVD
Published: 2018-10-01
Updated: 2018-11-14
Base Score: 4.3
Vector: CVSS2#AV:N/AC:M/Au:N/C:N/I:P/A:N
Severity: Medium
Base Score: 6.1
Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
EPSS: 0.0019