I checked HDP 2.6 and I see that it is running knox 0.11 which is affected by the WEBHDFS bug. It has been updated for HDP 2.5 but I haven't seen anything for HDP 2.6. Was knox patched or is an upgrade for HDP 2.6 in the works?
HDP 2.6 uses 0.12.0 version of knox according to :
Please run the following command on your knox host to find the exact version it has.
rpm -qa | grep knox