I ended up creating a custom ASP page following an example given here https://support.microsoft.com/en-us/help/224364/creating-a-directory-browsing-page-using-asp
If using a custom ASP page, directory browsing needs to be disabled, and the Default.asp
file placed in the folder that you want to be able to browse, and ASP functionality needs to be turned on for IIS.
The relevant ASP code written in vb script is copied below from the linked article
<%@LANGUAGE="VBSCRIPT"%>
<%
Option Explicit
On Error Resume Next
' this section is optional - it just denies anonymous access
If Request.ServerVariables("LOGON_USER")="" Then
Response.Status = "401 Access Denied"
End If
' declare variables
Dim objFSO, objFolder
Dim objCollection, objItem
Dim strPhysicalPath, strTitle, strServerName
Dim strPath, strTemp
Dim strName, strFile, strExt, strAttr
Dim intSizeB, intSizeK, intAttr, dtmDate
' declare constants
Const vbReadOnly = 1
Const vbHidden = 2
Const vbSystem = 4
Const vbVolume = 8
Const vbDirectory = 16
Const vbArchive = 32
Const vbAlias = 64
Const vbCompressed = 128
' don't cache the page
Response.AddHeader "Pragma", "No-Cache"
Response.CacheControl = "Private"
' get the current folder URL path
strTemp = Mid(Request.ServerVariables("URL"),2)
strPath = ""
Do While Instr(strTemp,"/")
strPath = strPath & Left(strTemp,Instr(strTemp,"/"))
strTemp = Mid(strTemp,Instr(strTemp,"/")+1)
Loop
strPath = "/" & strPath
' build the page title
strServerName = UCase(Request.ServerVariables("SERVER_NAME"))
strTitle = "Contents of the " & strPath & " folder"
' create the file system objects
strPhysicalPath = Server.MapPath(strPath)
Set objFSO = Server.CreateObject("Scripting.FileSystemObject")
Set objFolder = objFSO.GetFolder(strPhysicalPath)
%>
<html>
<head>
<title><%=strServerName%> - <%=strTitle%></title>
<meta name="GENERATOR" content="The Mighty Hand of Bob">
<style>
BODY { BACKGROUND: #cccccc; COLOR: #000000;
FONT-FAMILY: Arial; FONT-SIZE: 10pt; }
TABLE { BACKGROUND: #000000; COLOR: #ffffff; }
TH { BACKGROUND: #0000ff; COLOR: #ffffff; }
TD { BACKGROUND: #ffffff; COLOR: #000000; }
TT { FONT-FAMILY: Courier; FONT-SIZE: 11pt; }
</style>
</head>
<body>
<h1 align="center"><%=strServerName%><br><%=strTitle%></h1>
<h4 align="center">Please choose a file/folder to view.</h4>
<div align="center"><center>
<table width="100%" border="0" cellspacing="1" cellpadding="2">
<tr>
<th align="left">Name</th>
<th align="left">Bytes</th>
<th align="left">KB</th>
<th align="left">Attributes</th>
<th align="left">Ext</th>
<th align="left">Type</th>
<th align="left">Date</th>
<th align="left">Time</th>
</tr>
<%
''''''''''''''''''''''''''''''''''''''''
' output the folder list
''''''''''''''''''''''''''''''''''''''''
Set objCollection = objFolder.SubFolders
For Each objItem in objCollection
strName = objItem.Name
strAttr = MakeAttr(objItem.Attributes)
dtmDate = CDate(objItem.DateLastModified)
%>
<tr>
<td align="left"><b><a href="<%=strName%>"><%=strName%></a></b></td>
<td align="right">N/A</td>
<td align="right">N/A</td>
<td align="left"><tt><%=strAttr%></tt></td>
<td align="left"><b><DIR></b></td>
<td align="left"><b>Directory</b></td>
<td align="left"><%=FormatDateTime(dtmDate,vbShortDate)%></td>
<td align="left"><%=FormatDateTime(dtmDate,vbLongTime)%></td>
</tr>
<% Next %>
<%
''''''''''''''''''''''''''''''''''''''''
' output the file list
''''''''''''''''''''''''''''''''''''''''
Set objCollection = objFolder.Files
For Each objItem in objCollection
strName = objItem.Name
strFile = Server.HTMLEncode(Lcase(strName))
intSizeB = objItem.Size
intSizeK = Int((intSizeB/1024) + .5)
If intSizeK = 0 Then intSizeK = 1
strAttr = MakeAttr(objItem.Attributes)
strName = Ucase(objItem.ShortName)
If Instr(strName,".") Then strExt = Right(strName,Len(strName)-Instr(strName,".")) Else strExt = ""
dtmDate = CDate(objItem.DateLastModified)
%>
<tr>
<td align="left"><a href="<%=strFile%>"><%=strFile%></a></td>
<td align="right"><%=FormatNumber(intSizeB,0)%></td>
<td align="right"><%=intSizeK%>K</td>
<td align="left"><tt><%=strAttr%></tt></td>
<td align="left"><%=strExt%></td>
<td align="left"><%=objItem.Type%></td>
<td align="left"><%=FormatDateTime(dtmDate,vbShortDate)%></td>
<td align="left"><%=FormatDateTime(dtmDate,vbLongTime)%></td>
</tr>
<% Next %>
</table>
</center></div>
</body>
</html>
<%
Set objFSO = Nothing
Set objFolder = Nothing
' this adds the IIf() function to VBScript
Function IIf(i,j,k)
If i Then IIf = j Else IIf = k
End Function
' this function creates a string from the file atttributes
Function MakeAttr(intAttr)
MakeAttr = MakeAttr & IIf(intAttr And vbArchive,"A","-")
MakeAttr = MakeAttr & IIf(intAttr And vbSystem,"S","-")
MakeAttr = MakeAttr & IIf(intAttr And vbHidden,"H","-")
MakeAttr = MakeAttr & IIf(intAttr And vbReadOnly,"R","-")
End Function
%>