I have a problem dealing with encrypted URL parameters when applying HttpUtility.UrlEncode or UrlDecode.
for a given url string: ?fid=7kqguwhYMNw=&uid=YCRSGG71+58=
the PLUS sign which is part of the encrypted data of uid is stripped out and replaced with a space so my attempts to decrypt it fail.
OK, so I know that the + is a reserved shorthand for space in QUERYSTRING(RFC 1630) but since I don't have too much control over the value that is returned from encryption how can I get around this.
EDIT:
OK, so good point brought up. Ignore the UrlEncode/UrlDecode part of the question. Request.QueryString(["uid"]) will still have the plus sign stripped out of it when I pass it to my decryption method.
I would suggest adding code to remove the = characters, replace + with -, and replace / with .
s = s.Replace("=", "").Replace("+", "-").Replace("/", ".")
If you need to process the resulting string, you can do the reverse:
s = s.Replace(".", "/").Replace("-", "+")
(there is no reason to put back the = characters... they are merely padding).
That way you don't need to worry about URL encoding and decoding and it avoids unnecessary expansion of your string. It also looks more professional to users if they end up seeing the URL... percent signs in URL are ugly and almost always unnecessary... it screams "amateur" whenever I see them.
The Base-64 encoded value needs to be URL-encoded before it is put in the URL. If I do HttpUtility.UrlEncode("YCRSGG71+58=") then I get YCRSGG71%2b58%3d - which has no plus signs, and can be correctly decoded.
In other words, the code that is putting a base-64 value on the URL without encoding it first is wrong. If you control that code, you should change it. If you don't control that code, then don't try to decode something that wasn't url-encoded in the first place.
As a side remark, you should use HttpUtility.UrlEncode and HttpUtility.UrlDecode for this kind of work. However, even these wont help you since the URL is malformed anyway.
So, don't use anything at all! Since it's not encoded, why decode it?
Related
My server logs show a many attempts to access non existing sides. These are the "usual" bots scanning for known vulnerabilities. Many of the URLs contain =3D, e.g.
/?q=3Duser%2Fpassword&name%5B%23p=
/user/register/?element_parents=3Daccou=
/wp-admin/admin-post.php?swp_debug=3Dlo=
%3D is the url encoded value of = so I would expect to find %3D within the URL but not =3D. However, =3D can be found all over the logs. What is the meaning of this?
=3D is an example of a Quoted-Printable encoding for ASCII 0x3D, or the equals sign character (=).
You don't usually see this in URLs. It's not the normal encoding to use. It's a standard MIME type, an alternative to using base64. It looks like the request is expecting the app to decode the query string using Quoted-Printable, and then use the resulting path in some further redirect.
I have an ASP.NET Core web API and an issue with encoded URL's in query parameters.
I have an URL parameter like 'path/to/'. The IDENTIFIER part is something like 'HÄÄ/20/19'. This is urlEncoded in frontend to a link URL. The result is a link like
domain.com/new/stuff/path/to/H%C3%84%C3%84%2F20%2F19
Now, at some point, user gets redirected to a controller where this URL is used in a query parameter like:
param=%2Fpath%2Fto%2FH%C3%84%C3%84%2F20%2F19
I'm using request query to get the param
var param = HttpContext.Request.Query["param"].ToString();
After this the value of param is
%2Fpath%2Fto%2FHÄÄ%2F20%2F19
So the LATIN CAPITAL LETTER A WITH DIAERESIS are automatically decoded as the other encoded characters are not.
The actual problem comes when I'm redirecting the user to this URL. It ends up with a referer header where it causes havoc with an error message
System.InvalidOperationException: Invalid non-ASCII or control character in header: 0x00C4
I tried to just replace all the 'Ä' characters with 'A' and the problem is fixed. This is not a real fix though. I cannot encode the whole variable (see above) as it would result in double encoding for other encoded characters.
This problem only occurs with IE11 and Edge (AFAIK) and works fine with at least Chrome.
I'm not 100% sure where the actual problem is and why this is happening so does anyone have any ideas where to start looking and how to fix this without hacking with the string.replace?
EDIT
I could fix it with something like this, but I'm not seriously doing this. Seems way too hacky.
var problemPart = param.Substring(param.LastIndexOf('/') + 1, param.Length - param.LastIndexOf('/') - 1);
var fixedPart = WebUtility.UrlDecode(problemPart);
fixedPart = WebUtility.UrlEncode(fixedPart);
param = param.Replace(problemPart, fixedPart);
EDIT 2
I think the problem is that IE11 and Edge change the encoding by adding control characters to it when the URL ends up to the referer header. The fix I added to the original post doesn't actually fix the problem but just work around it. The control character that gets added to the URL is %C2%84 (so Ä becomes %C3%84%C2%84 instead of just %C3%84)
TEMPORARY WORKAROUND
I basically used the code above to workaround the issue. I iterated the parameter value and re-encoded all the invalid characters in it. This doesn't fix the root cause but works around the issue and user doesn't get any errors to the screen.
I have an encrypted query string passed from another page, it reads something like "/se73j+sef" but after receiving it, the '+' sign got omitted and became "/se73j sef". Is this normal? Please kindly advice. Thanks.
Is this normal?
Yes, perfectly normal. + is a special character in an url. It means space (0x20 ASCII character). If you want to represent the + sign you will have to url encode it:
/se73j%2Bsef
To url encode a string in .NET you could use the UrlEncode method. Or depending on how you are building the url there are certainly better ways.
In a recent project, I had the pleasure of troubleshooting a bug that involved images not loading when spaces were in the filename. I thought "What a simple issue, I'll UrlEncode() it!" But, NAY! Simply using UrlEncode() didn't resolve the problem.
The new problem was the HttpUtilities.UrlEncode() method switched spaces () to plusses (+) instead of %20 like the browser wanted. So file+image+name.jpg would return not-found while file%20image%20name.jpg was found correctly.
Thankfully, a coworker pointed out HttpUtilities.UrlPathEncode() to me which uses %20 for spaces instead of +.
WHY are there two ways of handling Url encoding? WHY are there two commands that behave so differently?
UrlEncode is useful for use with a QueryString as browsers tend to use a + here in place of a space when submitting forms with the GET method.
UrlPathEncode simply replaces all characters that cannot be used within a URL, such as <, > and .
Both MSDN links include this quote:
You can encode a URL using with the UrlEncode method or the
UrlPathEncode method. However, the methods return different results.
The UrlEncode method converts each space character to a plus character
(+). The UrlPathEncode method converts each space character into the
string "%20", which represents a space in hexadecimal notation. Use
the UrlPathEncode method when you encode the path portion of a URL in
order to guarantee a consistent decoded URL, regardless of which
platform or browser performs the decoding.
So in a URL you have the path and then a ? and then the parameters (i.e. http://some_path/page.aspx?parameters). URL paths encode spaces differently then the url parameters, that's why there is the two versions. For a long time spaces were not valid in a URL, but were in in the parameters.
In other words the formatting urls has changed over time. For a long time only ANSI chars could be in a URL too.
In some javascript, I have:
var url = "find.aspx?" + "location=" + encodeURIComponent( address );
alert( url );
location.href = url;
where the value of address is the string "Seattle, WA".
In the alert I see
find.aspx?Seattle%2C%20WA
as I expect.
But on the server side, when I look at Request.Url, the relevant substring I see is
find.aspx?Seattle, WA
And in the Firefox url window I see
find.aspx?location=Seattle%2C WA
So I'm getting three different representations whereas I would expect that in all three places I should see what I see in the alert. My expectation is that the url I assign to location.href should show up as-is in the browser url window, and should be passed as-is to the server in Request.Url (and I would need to decode the values on the server before using them). What's happening?
Firefox converts certain encoded characters into their literal forms as a way to be friendly to users. It will also convert spaces typed into the address bar into %20 for the server.
Update: The reason Firefox doesn't display the comma unencoded is because commas are allowed in URLs, but spaces are not, so it knows that a space is going to be unambiguously interpreted, whereas the pre-encoded comma is different from a non-encoded comma to some servers. see: Can I use commas in a URL?
ASP is probably trying to help you out by auto-un-encoding the string for you.
Update: It looks like ASP.NET unencodes Request.Url for you by default, as mentioned here: QueryString malformed after URLDecode They also mention that you can use HttpRequest.Url.Query to access the un-decoded version.
The alert is the only thing not doing any "magic" for you.
For the alert, you are doing the encoding yourself. Perhaps it looks the same as on the server-side if you removed encodeURIComponent.
On the server side, ASP.NET will always show you the unencoded form. This is to make it easier to directly map to files that also have text that needed to be (un)encoded.
Note that you can replace every letter for its UTF8 representation in URL Encoding. It will still be the same URL. I.e., type the following in the browser window and it will still work: %66%59%6E%64.aspx?location=Seattle%2C%20WA. To only encode the necessary chars, use UrlEncode on the server side if you create a link yourself.
URL encoding can become fairly tricky. You ask to explain it. To know the correct escape of a certain character, you need to know how that character looks in UTF8. The hexadecimal value of the UTF-8 bytes then become the %XX%YY value of your letter. Sometimes it's one %XX, but it can be up to six byte sequences in total (some Chinese characters for instance).
URL Encoding works one way only. Never double-encode or double-unencode. This is prohibited by the specification. Also, because you can encode any character, it is not always possible (as you found out) to do roundtrip encoding/unencoding. If you unencode and re-encode again, it is well possible that the resulting string is different, but syntactically the same.
In HTML, URL Encoding is sometimes interspersed with HTML Encoding. I.e., the ampersand is valid in HTML, but not in HTML. find.aspx?city=A&name=B becomes find.aspx?city=A&name=B in and HTML URL. However, browsers are lenient and will accept wrongly HTML-encoded strings.
Finally, a not on the browser: if you type in a space in a link, even inside an <a> tag, it will escape the space (or other character) for you. Likewise, it will nowadays show the odd characters (é, ï etc) in the address bar, but when it sends it over HTTP, the browser will correctly do the encoding for you.
Update: about anwering your question of needing a "definitive" reference or proof.
While I couldn't find any on the internet, I decided to look for it myself using Reflector. Going through the methods that set, for instance, the HttpRequest.QueryString, you quickly encounter the private method HttpRequest.FillInQueryStringCollection which then calls HttpValueCollection.FillfromEncodedBytes. Somewhat near the end of that method, HttpUtility.UrlDecode is called for the values. Conclusion: do not call it yourself, to prevent double decoding.
You can see this for yourself when you download Reflector and disassemble the .NET libs of System.Web.
For your example you can change this line
var url = "find.aspx?" + "location=" + encodeURIComponent( address );
to
var url = "find.aspx?" + "location=" + address;
and see the address as it is. Bu if address variable contains any '&' character your variable will be corrupt. So you are using encodeURIComponent to encode these things url.
On the Server side all these encoded strings are decoded back. It means encodeURIComponent is just for sending the address variable (whether it contains & character or not) to server side correctly.