Question

How do I allow only images using the FileUpload control

Asked by: Tricky1974

Hello!

On the contact page of our website we have a form which allows website users to send attachments with their email.

It all works great, but for the sake of security, I'd like it to only be able to send images.  It seems easy enough to just check the file extension, but this could easily be worked around by renaming the file.

Any help would be much appreciated.

try
            {
                System.Net.Mail.MailMessage myMail = new System.Net.Mail.MailMessage();
                myMail.To.Add("example@example.com");
                myMail.From = new MailAddress("example@example.com");
                myMail.Subject = "Email";
                myMail.IsBodyHtml = true;
                myMail.Body = "From: " + name + " (" + email + ") - (" + phone + ")<br /> Message: " + message;
 
                string fileName = Path.GetFileName(FileUpload1.PostedFile.FileName);
                Attachment myAttachment = new Attachment(FileUpload1.FileContent, fileName);
                    
                myMail.Attachments.Add(myAttachment);
 
                SmtpClient mySmtpClient = new SmtpClient("example.example.com");
                mySmtpClient.Send(myMail);
 
                pnlSent.Visible = true;
            }
            catch (Exception ex)
            {
                lblError.Text = ex.Message;
            }

                                  
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Asked On
2009-08-27 at 04:30:09ID24686152
Tags

Asp.net

,

C#

Topics

C# Programming Language

,

Programming for ASP.NET

,

Miscellaneous Web Development

Participating Experts
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Points
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Comments
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Answers

 

by: abelPosted on 2009-08-27 at 04:42:43ID: 25196783

I would choose to try to load the file as a Bitmap. You correctly state that it is possible to workaround (javascript or server side) file extension limitations. Note for instance the limits on EE: just rename any file to .txt and you can upload it (luckily so, because the original restrictions are far too confining).

The following should work for your situation, call it as in:

if(IsValidUpload(FileUpload1.FileContent))
  // valid

-- Abel --

private bool IsValidUpload(Stream stream)
{
    try
    {
        Bitmap bmp = Bitmap.FromStream(stream, false, true);
        return true;
    }
    catch (ArgumentException arg)
    {
        return false;
    }
}

                                              
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by: Tricky1974Posted on 2009-08-27 at 05:16:25ID: 25197048

Thanks for the response abel.

I'm getting an error when using the code though:

Cannot implicitly convert type 'System.Drawing.Image' to 'System.Drawing.Bitmap'. An explicit conversion exists (are you missing a cast?)

Any ideas?

 

by: abelPosted on 2009-08-27 at 05:40:58ID: 25197271

Ah, my mistake (I only checked syntax, didn't compile though), you need it like this, or you can remove the result, actually.

// correction for above
System.Drawing.Image img = Bitmap.FromStream(stream, false, true);
 
// or use this to discard the result right away
Bitmap.FromStream(stream, false, true);
                                              
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by: Tricky1974Posted on 2009-08-27 at 05:59:56ID: 25197474

That works perfectly abel.

Thanks for the help.

 

by: Tricky1974Posted on 2009-08-27 at 06:00:53ID: 31621159

This coupled together with abels other comment below is the full solution to this problem

20120131-EE-VQP-002

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