Both 1.5.8 and 1.6.5 have fixes for https://istio.io/latest/news/security/istio-security-2020-008/
You can read more about them in the 1.5.8 and 1.6.5 release notes pages.
1.5.8: https://istio.io/latest/news/releases/1.5.x/announcing-1.5.8/
1.6.5: https://istio.io/latest/news/releases/1.6.x/announcing-1.6.5/