Portainer 2.39.8

Includes security fixes, deprecations or config changes. Read the notes; usually worth updating soon.

From the release notes

• Upgraded kubectl in the kubectl shell image from 1.36.2 to 1.37.0, which is built with Go stdlib 1.26.6 and vendors golang.org/x/net 0.57.0, clearing 2 Critical findings (including CVE-2026-39821), 7 High and 7 Medium
• Deprecated and removed features
• Deprecated features