A critical flaw in 8 Atlassian Data Center products, which customers host themselves, allows an attacker with no login access to read specific files in each product's web application root directory.

The attacker must already know a file's exact name and path and cannot list what the directory holds. Atlassian disclosed the flaw, CVE-2026-21589, on October 5, rated it 9.3 out of 10, and