Getting 404 after add querystring in asp.net page

Question

I have a simple page that should display an image depending the path send it in the querystring. Im getting a 404 error code after I add the query string.

www.domain.com/ViewImage.aspx?Image=/img/image.jpg

ViewImage.aspx

<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">
    <title>Untitled Page</title>
</head>
<body>
    <form id="form1" runat="server">
    <table width="100%" cellpadding="0" cellspacing="0">
        <tr>
            <td align="center" valign="baseline">
                <img alt="image" id="Img2" runat="server" class="fullimage" src="" />
            </td>
        </tr>
    </table>
    </form>
</body>
</html>

ViewImage.aspx.cs

    protected void Page_Load(object sender, EventArgs e)
    {
        var src = Server.UrlDecode(this.Request.QueryString["Image"]);
        this.Img2.Src = validInput(src);
    }

    protected string validInput(string input)
    {
        var regex = "[\'<>\"]";
        if (null != input && !input.Contains("\"") && input.StartsWith("/"))
        {
                return !Regex.IsMatch(input, regex) ? AntiXssEncoder.XmlAttributeEncode(input):string.Empty;
        }
        return string.Empty;
    }

Expected result

<img alt="image" id="Img2" runat="server" class="fullimage" src="/img/image.jpg" />

Current result error 404

This is what I've tried and check:

Verified the page exist

www.domain.com/ViewImage.aspx is working fine, no src image set, but is finding the page correctly.

Verified the image exists

www.domain.com/img/image.jpg is working fine, img is displaying right.

Tried with a wrong path

www.domain.com/ViewImage.aspx?Image=/asdasdas/asdas.jpg Im not getting the 404 error and Image src is set right

Tried with only the folder and no image in the url

www.domain.com/ViewImage.aspx?Image=/img, this is not getting a 404 error, but if add the last slash I get the 404 error also.

www.domain.com/ViewImage.aspx?Image=/img/

This last url is getting a 404 error.

Notes :

We are using SSL in the server (https), not sure if this matters.
I'm thinking that probably the error can/should be fixed in the IIS configuration, not sure what or how to.

Any suggestions?

Can you try this: www.domain.com/ViewImage.aspx?Image=%2Fimg%2Fimage.jpg — sachin
– sachin, Commented Oct 3, 2016 at 21:16
Hi @sachin, thanks for your answer. I just tried, this was also the Jacob suggestion, but is not working. — JulioCesar
– JulioCesar, Commented Oct 3, 2016 at 21:34
There may be something unusual in your IIS config or web.config; those details could help. — Jacob
– Jacob, Commented Oct 3, 2016 at 21:46

Jacob · Accepted Answer · 2016-10-03 21:16:13Z

2

One thing to keep in mind is that / in query string values is not supported, though perhaps some browsers may be able to figure out encoding it for you when entering it in a URL. The path should be URI-encoded (%2F instead if /). It's possible that your server configuration is such where the / is being used in some sort of path resolution that is causing the 404; if your query string wasn't malformed, you may not have that issue.

You can also simplify your code a bit. Request.QueryString automatically decodes parameters, so you don't have to do that manually:

protected void Page_Load(object sender, EventArgs e)
{
    // The query string is automatically decoded
    var src = this.Request.QueryString["Image"]; 
    this.Img2.Src = validInput(src);
}

protected string validInput(string input)
{
    var regex = "[\'<>\"]";
    if (null != input && !input.Contains("\"") && input.StartsWith("/"))
    {
        return !Regex.IsMatch(input, regex) ? AntiXssEncoder.XmlAttributeEncode(input):string.Empty;
    }
    return string.Empty;
}

answered Oct 3, 2016 at 21:16

Jacob

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1 Comment

JulioCesar Over a year ago

Thanks for your answer, I just tried changing replacing the / with %2F but is not working, actually is weird that when I use ViewImage?Image=/asdasdas/asdasd.jpg the src in the image object is setting fine, the image is not found but have the src value. BTW, thanks for the Request.QueryString tip.

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