I get what you are saying but DP9 went out of committed support over 2 years ago. I fully understand all the reasons why one wouldn't / couldn't upgrade but honestly, I don't think the vendor is being unreasonable not patching software that went out of support over 2 years ago. Having said that, MF have released a patch for DP9.09, you can log a support case to get it. Full details can be found here: https://portal.microfocus.com/s/article/KM000003243?language=en_US 

You should probably thank the folks that are paying for extended support plus for DP9.09 (available until 31/12/2022) for this, its doubtful that it would be available otherwise, and I imagine that its just because of the criticality here, that MF is even making this available to DP9.09 customers without the extended support plus package...