Provide references for CVE-2021-39220.
Where can I find more information about CVE-2021-39220?
References are available at: https://github.com/nextcloud/security-advisories/security/advisories/GHSA-6q9v-wm8r-rcv5, https://github.com/nextcloud/mail/pull/5470, https://hackerone.com/reports/1308147.