Windows Volume Mount Points, Junctions and Windows 11 Firewall…

Posted on by dk

I was wondering why a simple firewall rule allowing inbound connections to some executable just would not work.

Extensive troubleshooting, excepting disabling the firewall (works), attempting relaxing any other conditions, like removing port restrictions (doesn’t work), source IP/subnet restrictions (doesn’t work), and a whole bunch of other stuff just simply did not work.

Finally frustrated, I just tried removing the targeted/allowed executable – port, source IP/subnet and other bits in place… WORKS.

WTF?

After more extensive testing, I finally discovered the issue: Windows Firewall fails to resolve executables from volumes mounted without drive letters. (a very direct, prompted summary from Google AI to try and explain this easily).

I mounted a volume as a directory junction only (see following output as an example).

PS C:\WINDOWS\system32> Get-Volume | Format-Table DriveLetter,FileSystem,FileSystemLabel,Path

DriveLetter FileSystem FileSystemLabel Path
----------- ---------- --------------- ----
          C NTFS       C Drive         \\?\Volume{guid#1}\
          T NTFS       TEMP            \\?\Volume{guid#2}\
                                       \\?\Volume{guid#3}\
                                       \\?\Volume{guid#4}\
            NTFS       WinRE           \\?\Volume{guid#5}\
            FAT32      EFI             \\?\Volume{guid#6}\
            NTFS       MountedVolume   \\?\Volume{guid#7}\

PS C:\WINDOWS\system32> Get-Item "C:\MountedVolume" | Format-List *

PSPath            : Microsoft.PowerShell.Core\FileSystem::C:\MountedVolume
PSParentPath      : Microsoft.PowerShell.Core\FileSystem::C:\
PSChildName       : MountedVolume
PSDrive           : C
PSProvider        : Microsoft.PowerShell.Core\FileSystem
PSIsContainer     : True
Mode              : d----l
BaseName          : MountedVolume
Target            : {Volume{guid#7}\}
LinkType          : Junction
Name              : MountedVolume
FullName          : C:\MountedVolume
Parent            :
Exists            : True
Root              : C:\
Extension         :
CreationTime      : 23/9/2021 10:23:43 am
CreationTimeUtc   : 23/9/2021 2:23:43 am
LastAccessTime    : 15/10/2025 10:53:42 pm
LastAccessTimeUtc : 15/10/2025 2:53:42 pm
LastWriteTime     : 23/9/2021 10:23:43 am
LastWriteTimeUtc  : 23/9/2021 2:23:43 am
Attributes        : Directory, ReparsePoint

Turns out Windows Firewall fails to resolve/recognise C:\MountedVolume\a.exe. 👿

The fix? As per the Google AI answer, just double-mount the volume with a direct drive letter – firewall rules will have to use that drive letter and path instead… 🙄

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