Windows disallows connections to localhost (ERR_NETWORK_ACCESS_DENIED)

I have the following problem:

Whenever I open http://localhost in my browser (doesn't matter which one, tested Google Chrome (49), Firefox, Edge, Internet Explorer), I'll get the message, that the connection could not be established. Chrome says: ERR_NETWORK_ACCESS_DENIED

When I try to connect via ssh with PuTTY I get "Network error: permission denied".

My setup (how it works since months):

I've a Windows 10 Pro 64-bit installed on an SSD inside an Acer Notebook. With VirtualBox I virtualize an Ubuntu 14.04 Linux VM which has one network adapter which is configured to NAT. With the built in functionality of VirtualBox I configured several port forwarding rules, mostly what you need:

Service       Proto       Host-IP       Host-Port       Guest-IP       Guest-Port
SSH           TCP         127.0.0.1     22              10.0.2.15       22
Parsoid       TCP         127.0.0.1     8142            10.0.2.15       8142
HTTP          TCP         127.0.0.1     80              10.0.2.15       80

Ok, that worked for months (like I said), I could connect with putty using host 127.0.0.1 and port 22, and also could open localhost in my browser to get the website hosted in the VM.

After nearly one day I've the problem I described above, and the only thing changed was:

• Installation of Windows updates:
  • Update für Microsoft Visual C++ 2012 Update 4 Redistributable Package (KB3119142)
• Update of Chrome to version 49

What I did so far to try to solve this problem (not ordered):

• Rolling back (using system recovery point of the Windows Update installation)
  • -> failed with error code 0x80070005
• Run Virus search with Kaspersky Internet Security and Malwarebytes Anti-Malware
  • -> without any negative result
• Shutting down the virtual machine (this should result in another error message?)
  • -> same error message as before
• Clearing my hosts file (no lines left, except the ones commented out, of courese)
  • -> same error message as before
• Turned off any firewall (after disconnecting from the internet) and security software that may result in such an error
  • -> same error message as before
• All network adapter drivers are up-to-date and working correctly (at least it seems so)

I think I forgot some things I already did :( Can anyone help or has any suggestion? If I forget to provide some information, feel free to ask :)

P.S.: And of course: Yes, I tried restarting the computer ;)