@schwabe I am not sure what cause problem and how it could be fixed properly. I double checked:

1. GetModuleFileNameW really returns lower case path.
2. QueryFullProcessImageNameW returns proper path.
3. Service is registered with proper path (ImagePath = C:\Program Files\OpenVPN...).
4. I think Windows for some reason attaches module (agent in our case) with wrong, lowered case path.

Man here has the same problem:
https://stackoverflow.com/questions/31239726/getmodulefilename-always-return-lowercase-in-service

From what I found, Windows doesn't allow to set entire drive as case-sensitive. So administator can set C:\Program Files as case-sensitive, but user still won't be able to create (to exploit possible vulnerability) C:\program files as C:\ still case-insensitive, because directory will already exist from NTFS perspective.

I tried fsutil.exe file setCaseSensitiveInfo C:\ enable but it responded "not supported".

Any comments in the new context?

I am not able to reproduce this. I used ovpnagent and ovpncliagent for testing, registered the service with ovpnagent install and checked that the server exe path is a case-sensitive.

We could use QueryFullProcessImageNameW to get the path - we already have all the code in place. Could you apply following patch and see if that works for you?

diff --git a/openvpn/win/modname.hpp b/openvpn/win/modname.hpp
index 00142dd1..d3cafb45 100644
--- a/openvpn/win/modname.hpp
+++ b/openvpn/win/modname.hpp
@@ -32,20 +32,15 @@
 #include <openvpn/common/wstring.hpp>
 #include <openvpn/win/winerr.hpp>
 #include <openvpn/win/reg.hpp>
+#include <openvpn/win/npinfo.hpp>
 
 namespace openvpn {
 namespace Win {
 
 inline std::wstring module_name()
 {
-    // get path to our binary
-    wchar_t path[MAX_PATH];
-    if (!::GetModuleFileNameW(NULL, path, MAX_PATH))
-    {
-        const Win::LastError err;
-        OPENVPN_THROW_EXCEPTION("GetModuleFileNameW failed: " << err.message());
-    }
-    return std::wstring(path);
+    auto current_process_handle = NamedPipePeerInfo::get_process(GetCurrentProcessId(), true);
+    return NamedPipePeerInfo::get_exe_path(current_process_handle());
 }
 
 inline std::string module_name_utf8()