System.Net.WebClient doesn't work with Windows Authentication
iis, ntlm, webclient
Solution
I have seen a similar issue, where the Integrated / NTLM security will only work if you are accessing the host by machine name or localhost. In fact, it is a [poorly] document feature in Windows that is designed to protect against "reflection attacks".
Basically, you need to create a registry key on the machine that is trying to access the server, and whitelist the domain you are trying to hit. Each host name / FQDN needs to be on it's own line - there are no wildcards and the name must match exactly. From the KB Article:
- Click Start, click Run, type regedit, and then click OK.
- In Registry Editor, locate and then click the following registry key: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa\MSV1_0
- Right-click MSV1_0, point to New, and then click Multi-String Value.
- Type BackConnectionHostNames, and then press ENTER.
- Right-click BackConnectionHostNames, and then click Modify.
- In the Value data box, type the host name or the host names for the sites that are on the local computer, and then click OK.
- Exit Registry Editor, and then restart the computer.
http://support.microsoft.com/kb/956158/en-us
Problem
I am trying to use System.Net.WebClient in a WinForms application to upload a file to an IIS6 server which has Windows Authentication as it only 'Authentication' method. ``` WebClient myWebClient = new WebClient(); myWebClient.Credentials = new System.Net.NetworkCredential(@"boxname\peter", "mypassword"); byte[] responseArray = myWebClient.UploadFile("http://localhost/upload.aspx", fileName); ``` I get a 'The remote server returned an error: (401) Unauthorized', actually it is a 401.2 Both client and IIS are on the same Windows Server 2003 Dev machine. When I try to open the page in Firefox and enter the same correct credentials as in the code, the page comes up. However when using IE8, I get the same 401.2 error. Tried Chrome and Opera and they both work. I have 'Enable Integrated Windows Authentication' enabled in the IE Internet options. The Security Event Log has a Failure Audit: ``` Logon Failure: Reason: An error occurred during logon User Name: peter Domain: boxname Logon Type: 3 Logon Process: ÈùÄ Authentication Package: NTLM Workstation Name: boxname Status code: 0xC000006D Substatus code: 0x0 Caller User Name: - Caller Domain: - Caller Logon ID: - Caller Process ID: - Transited Services: - Source Network Address: 127.0.0.1 Source Port: 1476 ``` I used Process Monitor and Fiddler to investigate but to no avail. Why would this work for 3rd party browsers but not with IE or System.Net.WebClient?