Given the message in a messages properties file:
message = Change relation <strong>{0}</strong> -> <strong>{1}</strong> to <strong>{2}</strong> -> <strong>{3}</strong>?
if the content of any of the placeholders is a user-influenced string, I need to html escape the message in order to prevent a potential XSS (I do that by using the c:out tag in my JSP templates, I guess I could use the htmlEscape-attribute of the spring:message tag as well, but I think there's no difference).
However by doing so, I corrupt the markup in the message, <strong> etc. which leads to the output:
Change relation <strong>Peter</strong> -> <strong>Car</strong> to <strong>Carl</strong> -> <strong>Bus</strong>?
I've already read the thread here on stackoverflow but it does not address XSS.
I am thinking about these options:
1) Simply replace all <strong> tags from the messages properties files with single quotes. Then there's no problem html escaping the entire message, with the drawback of a little less highlighting of the specific parts of the message.
2) Split the message into parts which allow for separate markup in the (JSP) template. This feels like much work just to get the markup right.
Am I missing something here? Which is the better option, or is there another option?
Edit: Without html-escaping the message is, like I want it to be, like this:
Change relation Peter -> Car to Carl -> Bus?
So the html-markup as in the messages.properties file is being rendered when displayed in the template.
When escaping, the message is like above, showing me the <strong> tags instead of rendering them.
Going under the assumption that you are getting the following output:
Change relation <strong>Peter</strong> -> <strong>Car</strong> to <strong>Carl</strong> -> <strong>Bus</strong>
It looks like you are escaping your entire HTML string rather than just the part that needs to be escaped.
You should escape each {#} value on its own, and then place it into the HTML. The general values you need to escape are: <, >, ', ", and &, but use an anti-xss library and templating system if you can.
Once you've escaped all the potentially dangerous parts, you can use something like <c:out value="${msg}" escapeXml="false"/>. This is not a language/framework I know, but you need some way to output the actual HTML vs the escaped version. Whatever way you prefer should be fine as long as you properly escape the untrusted part.
I would like to know if I can protect my website against XSS attacks by replacing ONLY < and > by < and > or am I missing something.
Example :
<?php echo '<div>' . $escaped . '</div>' ?>
I already know htmlspecialchars PHP function & affiliates
No, for the HTML body you will also need to encode the & character to prevent an attacker from potentially escaping the escape.
Check out the XSS Experimental Minimal Encoding Rules:-
HTML Body (up to HTML 4.01):
HTML Entity encode < &
specify charset in metatag to avoid UTF7 XSS
XHTML Body:
HTML Entity encode < & >
limit input to charset http://www.w3.org/TR/2008/REC-xml-20081126/#charsets
Note that if you want to enter stuff inside of an attribute value, then you need to properly encode all characters with special meaning. The XSS (Cross Site Scripting) Prevention Cheat Sheet mentions to encode the following characters:-
&,<, >, ", ', /
You must also quote the attribute value for the escaping to be effective.
The answer is no, someone will find his way to exploit it, somehow.
You are underestimating the number of techniques and the creativity of attackers. Read through the OWASP XSS Cheat Sheet https://www.owasp.org/index.php/XSS_Filter_Evasion_Cheat_Sheet to have an idea of the number of ways this could happen. In your case, does it protect against an XSS into an onload attribute? Or into an input that becomes part of a CSS definition? In those situations you already are into an implicit tag, so you only need JS code to be added, no reason to use '<' or '>'
Do output validation with XSS, it is the simplest thing and it will protect you everywhere, just do it every single time you write anything (no matter if it comes from the user or not) and pay attention to the context (escape/encode for an URL when you are writing a link, escape/encode for JS when you are writing directly into a JS script, escape/encode for CSS when you are writing part of a CSS definition, escape/encode JSON when you write JSON data, escape/encode HTML in any other case).
In addition, even if it is unrelated, I usually point to this site to show how people like to be creative about JS http://www.jsfuck.com/ - this is meant to be obfuscation-only but I used it for evading anti-XSS controls, usually when made by a 3rd party.
I've been running into a problem that was revealed through our Google adwords-driven marketing campaign. One of the standard parameters used is "region". When a user searches and clicks on a sponsored link, Google generates a long URL to track the click and sends a bunch of stuff along in the referrer. We capture this for our records, and we've noticed that the "Region" parameter is coming through incorrectly. What should be
http://ravercats.com/meow?foo=bar®ion=catnip
is instead coming through as:
http://ravercats.com/meow?foo=bar®ion=catnip
I've verified that this occurs in all browsers. It's my understanding that HTML entity syntax is defined as follows:
&VALUE;
where the leading boundary is the ampersand and the closing boundary is the semicolon. Seems straightforward enough. The problem is that this isn't being respected for the ® entity, and it's wreaking all kinds of havoc throughout our system.
Does anyone know why this is occurring? Is it a bug in the DTD? (I'm looking for the current HTML DTD to see if I can make sense of it) I'm trying to figure out what would be common across browsers to make this happen, thus my looking for the DTD.
Here is a proof you can use. Take this code, make an HTML file out of it and render it in a browser:
<html>
http://foo.com/bar?foo=bar®ion=US®ister=lowpass®_test=fail&trademark=correct
</html>
EDIT: To everyone who's suggesting that I need to escape the entire URL, the example URLs above are exactly that, examples. The real URL is coming directly from Google and I have no control over how it is constructed. These suggestions, while valid, don't answer the question: "Why is this happening".
Although valid character references always have a semicolon at the end, some invalid named character references without a semicolon are, for backward compatibility reasons, recognized by modern browsers' HTML parsers.
Either you know what that entire list is, or you follow the HTML5 rules for when & is valid without being escaped (e.g. when followed by a space) or otherwise always escape & as & whenever in doubt.
For reference, the full list of named character references that are recognized without a semicolon is:
AElig, AMP, Aacute, Acirc, Agrave, Aring, Atilde, Auml, COPY, Ccedil,
ETH, Eacute, Ecirc, Egrave, Euml, GT, Iacute, Icirc, Igrave, Iuml, LT,
Ntilde, Oacute, Ocirc, Ograve, Oslash, Otilde, Ouml, QUOT, REG, THORN,
Uacute, Ucirc, Ugrave, Uuml, Yacute, aacute, acirc, acute, aelig,
agrave, amp, aring, atilde, auml, brvbar, ccedil, cedil, cent, copy,
curren, deg, divide, eacute, ecirc, egrave, eth, euml, frac12, frac14,
frac34, gt, iacute, icirc, iexcl, igrave, iquest, iuml, laquo, lt,
macr, micro, middot, nbsp, not, ntilde, oacute, ocirc, ograve, ordf,
ordm, oslash, otilde, ouml, para, plusmn, pound, quot, raquo, reg,
sect, shy, sup1, sup2, sup3, szlig, thorn, times, uacute, ucirc,
ugrave, uml, uuml, yacute, yen, yuml
However, it should be noted that only when in an attribute value, named character references in the above list are not processed as such by conforming HTML5 parsers if the next character is a = or a alphanumeric ASCII character.
For the full list of named character references with or without ending semicolons, see here.
This is a very messy business and depends on context (text content vs. attribute value).
Formally, by HTML specs up to and including HTML 4.01, an entity reference may appear without trailing semicolon, if the next character is not a name character. So e.g. ®ion= would be syntactically correct but undefined, as entity region has not been defined. XHTML makes the trailing semicolon required.
Browsers have traditionally played by other rules, though. Due to the common syntax of query URLs, they parse e.g. href="http://ravercats.com/meow?foo=bar®ion=catnip" so that ®ion is not treated as an entity reference but as just text data. And authors mostly used such constructs, even though they are formally incorrect.
Contrary to what the question seems to be saying, href="http://ravercats.com/meow?foo=bar®ion=catnip" actually works well. Problems arise when the string is not in an attribute value but inside text content, which is rather uncommon: we don’t normally write URLs in text. In text, ®ion= gets processed so that ® is recognized as an entity reference (for “®”) and the rest is just character data. Such odd behavior is being made official in HTML5 CR, where clause 8.2.4.69 Tokenizing character references describes the “double standard”:
If the character reference is being consumed as part of an attribute,
and the last character matched is not a ";" (U+003B) character, and
the next character is either a "=" (U+003D) character or in the range
ASCII digits, uppercase ASCII letters, or lowercase ASCII letters,
then, for historical reasons, all the characters that were matched
after the U+0026 AMPERSAND character (&) must be unconsumed, and
nothing is returned.
Thus, in an attribute value, even ®= would not be treated as containing a character reference, and still less ®ion=. (But reg_test= is a different case, due to the underscore character.)
In text content, other rules apply. The construct ®ion= causes then a parse error (by HTML5 CR rules), but with well-defined error handling: ® is recognized as a character reference.
Maybe try replacing your & as &? Ampersands are characters that must be escaped in HTML as well, because they are reserved to be used as parts of entities.
1: The following markup is invalid in the first place (use the W3C Markup Validation Service to verify):
In the above example, the & character should be encoded as &, like so:
2: Browsers are tolerant; they try to make sense out of broken HTML. In your case, all possibly valid HTML entities are converted to HTML entities.
Here is a simple solution and it may not work in all instances.
So from this:
http://ravercats.com/meow?status=Online®ion=Atlantis
To This:
http://ravercats.com/meow?region=Atlantis&status=Online
Because the ® as we know triggers the special character ®
Caveat: If you have no control over the order of your URL query string parameters then you'll have to change your variable name to something else.
Escape your output!
Simply enough, you need to encode the url format into html format for accurate representation (ideally you would do so with a template engine variable escaping function, but barring that, with htmlspecialchars($url) or htmlentities($url) in php).
See your test case and then the correctly encoded html at this jsfiddle:
http://jsfiddle.net/tchalvakspam/Fp3W6/
Inactive code here:
<div>
Unescaped:
<br>
http://foo.com/bar?foo=bar®ion=US®ister=lowpass®_test=fail&trademark=correct
</div>
<div>
Correctly escaped:
<br>
http://foo.com/bar?foo=bar®ion=US®ister=lowpass®_test=fail&trademark=correct
</div>
It seems to me that what you have received from google is not an actual URL but a variable which refers to a url (query-string). So, thats why it's being parsed as registration mark when rendered.
I would say, you owe to url-encode it and decode it whenever processing it. Like any other variable containing special entities.
To prevent this from happening you should encode urls, which replaces characters like the ampersand with a % and a hexadecimal number behind it in the url.
I have a PHP script that will generate <input>s dynamically, so I was wondering if I needed to filter any characters in the name attribute.
I know that the name has to start with a letter, but I don't know any other rules. I figure square brackets must be allowed, since PHP uses these to create arrays from form data. How about parentheses? Spaces?
Note, that not all characters are submitted for name attributes of form fields (even when using POST)!
White-space characters are trimmed and inner white-space characters as well the character . are replaced by _.
(Tested in Chrome 23, Firefox 13 and Internet Explorer 9, all Win7.)
Any character you can include in an [X]HTML file is fine to put in an <input name>. As Allain's comment says, <input name> is defined as containing CDATA, so the only things you can't put in there are the control codes and invalid codepoints that the underlying standard (SGML or XML) disallows.
Allain quoted W3 from the HTML4 spec:
Note. The "get" method restricts form data set values to ASCII characters. Only the "post" method (with enctype="multipart/form-data") is specified to cover the entire ISO10646 character set.
However this isn't really true in practice.
The theory is that application/x-www-form-urlencoded data doesn't have a mechanism to specify an encoding for the form's names or values, so using non-ASCII characters in either is “not specified” as working and you should use POSTed multipart/form-data instead.
Unfortunately, in the real world, no browser specifies an encoding for fields even when it theoretically could, in the subpart headers of a multipart/form-data POST request body. (I believe Mozilla tried to implement it once, but backed out as it broke servers.)
And no browser implements the astonishingly complex and ugly RFC2231 standard that would be necessary to insert encoded non-ASCII field names into the multipart's subpart headers. In any case, the HTML spec that defines multipart/form-data doesn't directly say that RFC2231 should be used, and, again, it would break servers if you tried.
So the reality of the situation is there is no way to know what encoding is being used for the names and values in a form submission, no matter what type of form it is. What browsers will do with field names and values that contain non-ASCII characters is the same for GET and both types of POST form: it encodes them using the encoding the page containing the form used. Non-ASCII GET form names are no more broken than everything else.
DLH:
So name has a different data type for than it does for other elements?
Actually the only element whose name attribute is not CDATA is <meta>. See the HTML4 spec's attribute list for all the different uses of name; it's an overloaded attribute name, having many different meanings on the different elements. This is generally considered a bad thing.
However, typically these days you would avoid name except on form fields (where it's a control name) and param (where it's a plugin-specific parameter identifier). That's only two meanings to grapple with. The old-school use of name for identifying elements like <form> or <a> on the page should be avoided (use id instead).
The only real restriction on what characters can appear in form control names is when a form is submitted with GET
"The "get" method restricts form data set values to ASCII characters." reference
There's a good thread on it here.
While Allain's comment did answer OP's direct question and bobince provided some brilliant in-depth information, I believe many people come here seeking answer to more specific question: "Can I use a dot character in form's input name attribute?"
As this thread came up as first result when I searched for this knowledge I guessed I may as well share what I found.
Firstly, Matthias' claimed that:
character . are replaced by _
This is untrue. I don't know if browser's actually did this kind of operation back in 2013 - though, I doubt that. Browsers send dot characters as they are(talking about POST data)! You can check it in developer tools of any decent browser.
Please, notice that tiny little comment by abluejelly, that probably is missed by many:
I'd like to note that this is a server-specific thing, not a browser thing. Tested on Win7 FF3/3.5/31, IE5/7/8/9/10/Edge, Chrome39, and Safari Windows 5, and all of them sent " test this.stuff" (four leading spaces) as the name in POST to the ASP.NET dev server bundled with VS2012.
I checked it with Apache HTTP server(v2.4.25) and indeed input name like "foo.bar" is changed to "foo_bar". But in a name like "foo[foo.bar]" that dot is not replaced by _!
My conclusion: You can use dots but I wouldn't use it as this may lead to some unexpected behaviours depending on HTTP server used.
Do you mean the id and name attributes of the HTML input tag?
If so, I'd be very tempted to restrict (or convert) allowed "input" name characters into only a-z (A-Z), 0-9 and a limited range of punctuation (".", ",", etc.), if only to limit the potential for XSS exploits, etc.
Additionally, why let the user control any aspect of the input tag? (Might it not ultimately be easier from a validation perspective to keep the input tag names are 'custom_1', 'custom_2', etc. and then map these as required.)
I have a form using the GET method.
If values are submitted with special characters, they appear in the URI as:
?value=fudge%20and%20stuff
How do I make it clean?
I don't want to use the header function because this is happening within a page in drupal.
A URL cannot contain spaces and many other "special characters", therefore they get encoded. Unfortunately there isn't a lot you can do about it. The most you could do is some JavaScript trickery in the form, but I don't think it's worth it.
If %20 bothers you, you can substitute (GREP replace) the + character (?value=fudge+and+stuff) for better readability. Otherwise there's not a lot you can do. Other "exotic" characters will be similarly escaped, and need to be.
URL :?value=fudge%20and%20stuff
Encoded as: fulg< space > and < space >stuff