BREAKING: Exploited Atlassian bug lets strangers read files off Jira, Confluence and Bitbucket Data Center, now on CISA KEV (CVE-2026-21589)

How to fix CVE-2026-21589: upgrade Jira, Confluence, Bitbucket and other Atlassian Data Center apps to the Oct 5 fixed releases. Exploited, CISA KEV due Oct 18.