The Widget Connector macro in Atlassian Confluence Server before version 6.6.12 (the fixed version for 6.6.x), from version 6.7.0 before 6.12.3 (the fixed version for 6.12.x), from version 6.13.0 before 6.13.3 (the fixed version for 6.13.x), and from version 6.14.0 before 6.14.2 (the fixed version for 6.14.x), allows remote attackers to achieve path traversal and remote code execution on a Confluence Server or Data Center instance via server-side template injection.
https://www.greynoise.io/blog/spike-in-atlassian-exploitation-attempts-patching-is-crucial
https://www.tenable.com/cyber-exposure/a-look-inside-the-ransomware-ecosystem
https://www.cisa.gov/news-events/cybersecurity-advisories/aa21-209a
https://github.com/odaysec/confluPwn
https://github.com/HK4zCzi/CVE-2019-3396-Velocity-Server-Side-Template-Injection
https://github.com/pwnosec/jira-vuln-scanner
https://github.com/Avento/CVE-2019-3396-Memshell-for-Behinder
https://github.com/imhunterand/JiraCVE
https://github.com/wjl110/CVE-Master
https://github.com/skommando/CVE-2019-3396-confluence-poc
https://github.com/tanw923/test1
https://github.com/vntest11/confluence_CVE-2019-3396
https://github.com/jas502n/CVE-2019-3396
https://github.com/Yt1g3r/CVE-2019-3396_EXP
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2019-3396
https://jira.atlassian.com/browse/CONFSERVER-57974
https://euvd.enisa.europa.eu/vulnerability/EUVD-2019-13035
http://packetstormsecurity.com/files/161065/Atlassian-Confluence-6.12.1-Template-Injection.html