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Questions tagged [xss]

Cross-Site Scripting: An attack method that involves injection of code or markup into a webpage. There are three major types of XSS: Reflected XSS, Stored XSS (aka persistent XSS) and DOM-based XSS (aka client side XSS).

88
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4answers
16k views

How does XSS work? [closed]

I have very little experience in web development, but I'm interested in security. However, I haven't fully understood how XSS works. Can you explain it to med? The Wikipedia article give me a good ...
24
votes
6answers
6k views

Filter user input before the database or upon display?

Given a web application where user data must be properly escaped to avoid XSS, is it better to try to remove the "bad stuff" before it enters the database, or is it best to allow it in the database ...
14
votes
2answers
9k views

UTF-7 XSS attacks in modern browsers

I've recently read Ned Batchelders article on UTF-7 XSS-attacks. I tested his examples, but could not get any UTF-7 attack to work in modern browsers. I tried recent versions of Firefox, Chrome and ...
24
votes
2answers
6k views

XSS prevention through Content Security Policy

How can Content Security Policy (CSP) significantly reduce the risk and impact of XSS attacks in modern browsers? Is it possible to circumvent CSP in order to execute XSS?
22
votes
1answer
6k views

Does the practice of blocking an off-site “Referer:” HTTP requests improve website security?

Is there any benefit for a security-paranoid website to disallow HTTP requests that have a Referer: from 3rd party sites? The pitch is that if such a HTTP request were to come in, then certain XSS ...
12
votes
4answers
14k views

PHP functions for preventing XSS

Is there a proven library with functions for preventing XSS attacks? Many people don't realise that htmlspecialchars is not enough to prevent XSS attacks. There are various contexts that need their ...
7
votes
1answer
1k views

XSS inside HTML attribute where < and " are filtered

Is it possible to bypass an XSS filter where < and " are encoded as &lt; and &quot;, but > is not escaped? My data is injected into an HTML value attribute. However I can't get out of ...
0
votes
1answer
2k views

XSS payload without using < and >

I am performing testing on a site that takes input from the user and places it between <span> and </span>. However, < and > from the user are encoded as &lt and &gt. Is ...
52
votes
5answers
14k views

IMG tag vulnerability

Is it safe to display images from arbitrary domains? I.e. let's say I have an image on my page: <img src="http://badguy.com/image.gif" /> What if image.gif will return some js attack vector, ...
18
votes
4answers
2k views

Web Security Cheatsheet / ToDo list

Can anyone suggest a cheatsheet or ToDo list of web site and application security? A local small business owner prompted a question about web security, basically her company website just got XSS ...
3
votes
1answer
13k views

exploiting XSS in jQuery selector

My static code analyser flags this piece of Javascript on my client's web site as a potential DOM based XSS: var x = $('#' + window.location.hash.substr(1)) x.addClass('highlighted').find('div').show(...
10
votes
4answers
1k views

Is XSS possible when < is not escaped, but also not displayed if followed by a character?

I have figure out that < wasn't encoded as &lt;. Instead of that, it is simply not sent by the server if it is directly followed by something. For example, <a will display nothing. But I'm ...
78
votes
8answers
37k views

What could an “<img src=” XSS do?

Most WAFs when blocking XSS will block obvious tags like script and iframe, but they don't block img. Theoretically, you can img src='OFFSITE URL', but what's the worse that can happen? I know you ...
11
votes
1answer
19k views

Preventing XSS for REST API

I have a spring REST API and a client project. Client projects' HTML page uses jquery ajax calls to fetch data from REST API using json or xml format. My question is to avoid XSS attacks on a web page,...
13
votes
3answers
16k views

Is it possible to inject HTML into image to provoke XSS?

Some answers mention that it's possible to inject attacker-controlled HTML into images and therefore provoke XSS. I guess that this HTML will be processed by browser only if hole exists in browser. ...
6
votes
2answers
14k views

HTML encoding to protect against XSS

While going through some references about protection against XSS i found that it is a good practice to encode data (entered by users) before using it to generate a dynamic page. I was not able to find ...
5
votes
7answers
19k views

Current best practices to prevent persistent XSS attacks

I have a text field that allows the user to type whatever he/she wants. After saving, the results are later displayed on the screen to potentially many people. XSS seems a bit like black magic to me,...
6
votes
1answer
640 views

Style attribute XSS without quotes

If there is a page that allows user input into the following... .page { background: #userinput; } can it be exploited if <>'" are all filtered? I've seen width: expression(alert(0));, but ...
5
votes
1answer
5k views

Is it possible to exploit XSS inside User-Agent header? [duplicate]

I've found an xss bug inside user-agent header on one popular buy/sell site , and after reporting it to them , they answered that it is not dangerous as it can not be exploited without user ...
-2
votes
1answer
410 views

Why isn't this code running? [closed]

I found an area on a site (can't disclose name) that allows you to put input, and returns it in this form: <p> <strong>text here</strong> </p> It isn't filtered, so you ...
4
votes
3answers
1k views

Flash ignores Content-Type header, allowing XSS?

I recently read that the Flash plugin ignores the Content-Type header in certain circumstances. In particular, you can give Flash a URL, and the Flash plugin will happily fetch the content at that ...
2
votes
2answers
2k views

XSS via REQUEST_URI

Is there any situation where an XSS attack can be performed via the PHP $_SERVER['REQUEST_URI'] variable? For those unfamiliar with it: It contains the complete URL used to access that website, ...
49
votes
5answers
10k views

New XSS cheatsheet? [closed]

There is a great list of XSS vectors avaliable here: http://ha.ckers.org/xss.html, but It hasn't changed much lately (eg. latest FF version mentioned is 2.0). Is there any other list as good as this, ...
42
votes
2answers
9k views

How do I use Markdown securely?

How do I use the Markdown library safely? What do I need to do to make sure that its output is safe to include into my web page? I want to allow untrusted users to enter content (in Markdown format)....
21
votes
3answers
14k views

Cross Site Scripting without special chars

I'm testing a web application and I found a XSS vulnerability. I can break a tag and inject some code to the application but nothing potentialy dangerous for the client. The application has a filter ...
16
votes
4answers
16k views

What is the danger of Reflected Cross Site Scripting?

What is the danger of Reflected Cross Site Scripting? I understand the Reflected XSS is dangerous, because it's possible. But what practical attacks can be performed using Reflected XSS?
17
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2answers
5k views

Will same-site cookies be sufficent protection against CSRF and XSS?

I must say, that I like this idea and it seems that it will bring a new form of protection against CSRF and XSS or at least it will reduce those attacks. So, how effective will this protection be? ...
13
votes
1answer
18k views

Does Google Chrome protect against cross site scripting (XSS)?

In Firefox I've been using the NoScript extension to protect myself from certain kinds of malware attacks. NoScript is well known as a very powerful extension for Firefox and introduced protection ...
15
votes
5answers
13k views

Does setting httponly prevent stealing a session using XSS?

If a session token is stored in a cookie that has httponly set, is there any way that a XSS vulnerability could allow a malicious user to steal a users session token?
20
votes
6answers
13k views

Is Chrome completely secure against Reflected XSS?

I notice that Chrome does not execute scrips that are part of the web request, http://vulnerable_site?pageTitle=<script>alert('xss')</script> With such links since the script is as part ...
14
votes
1answer
5k views

Cross site scripting and the use of http-only cookies?

I have been a developer and now I am trying to look at XSS from the point of view of a developer. I was thinking of a particular case of reflected XSS . Let us say we have a vulnerable website and if ...
15
votes
3answers
6k views

How serious are XSS attacks

A website I visit allows this kind of attack, to be implemented with GET in the URL <SCRIPT SRC=http://ha.ckers.org/xss.js></SCRIPT> Along with many others on this page: http://ha.ckers....
13
votes
7answers
3k views

Whitelisting DOM elements to defeat XSS

As we know, developers are responsible for correctly escaping/validating data provided by the user before rendering or storing them. However, we must agree that it's relatively easy to forget a single ...
3
votes
1answer
3k views

Does a Content-Type: text/plain header protect against XSS in browsers?

I'm creating a small web script that mostly redirects the browser but has some error conditions when input parameters cannot be validated. I'd like to display error messages like parameter XXX had ...
11
votes
2answers
2k views

How reliable is ASP.NET's Request Validation feature?

ASP.NET offers an extra layer to protect your application from XSS attacks and injection in general which is called Request validation. On their official topic, they mention that: Even if you're ...
5
votes
2answers
10k views

What is the difference between ordinary XSS and Dom XSS vulnerabilities? [duplicate]

I'm not a computer guy, but just out of curiosity I've recently started to learn PHP for programming my own website and I've read about some most common vulnerabilities that exist in web applications. ...
2
votes
2answers
1k views

Reflected XSS quote not encoded

I am attempting to exploit URL with a reflected XSS as follows: http://domain.com/vuln_parm= The contents of vuln_parm gets returned to the user as follows: <div attrib1="" attrib2="" vulnattrib=...
2
votes
2answers
11k views

How to prevent XSS from url

I found an XSS vulnerability which is exploited by appending attack in the URL parameters. For eg. the original URL site.com/?s=login&m=forgotten And the attack URL site.com/?s=login&m=...
1
vote
3answers
3k views

Reflective XSS in script codes with Content Type “text/javascript”

I have a webpage that returns raw script code with the headerContent-Type: text/javascript. However I found that there is a reflective xss in one of the parameters passed to the url which is copied ...
47
votes
1answer
21k views

Is Django's built-in security enough?

I have learned that Django provides built-in protection against the three main types of web app attacks (SQL injection, XSS and CSRF), which is really awesome. Yet I have spoken to a few Django ...
20
votes
1answer
28k views

Difference between XSS and CSRF? [closed]

I know about cross-site scripting and cross-site request forgery. I want to know if there is any similarity between them?
41
votes
3answers
15k views

How does CORS prevent XSS?

I recently learned about CORS and got the impression that its purpose is to prevent XSS. With CORS, the browser blocks requests to different domains, unless particular headers are in place. But if a ...
12
votes
2answers
9k views

How does BeEF work and how can it be persistent?

BeEF - the browser exploitation framework. I think (thought) I had a basic working understanding of how it works. Recently, though, I was watching, this DEFCON talk, where a hacker used a man-in-the-...
15
votes
6answers
4k views

Solution to allow JavaScript input but prevent XSS

We have a simple Blog system that allows users to input html and JavaScript to build a blog page. I'm aware that allowing javascript open up the door to xss attacks. We do however need to allow users ...
12
votes
5answers
7k views

CSRF protection with Session Id

To protect against CSRF, couldn't my page javascript just dynamically insert the session id from the cookie into the body of each HTTP request right before it's sent? The server would then just ...
10
votes
3answers
5k views

How bad is a Self Contained XSS attack?

Some of you might be familiar with this attack called Self Contained XSS. I recently stumbled upon this article about it. So how bad this kind of attack can be, even though this doesn't have access to ...
12
votes
3answers
1k views

Is stripping out < and > characters an effective way of preventing XSS?

I'm guessing that HTML encoding the input would probably be a better solution, but I'm curious if just stripping out any < and > characters would be an effective defense against XSS attacks. ...
9
votes
1answer
1k views

Proper way to protect against XSS, when output is directly into JS not HTML?

I'm seeing plenty of examples when the output is going into HTML directly, but I'm seeing more conflicting information when the output is going straight into JS. For example if the code was: var ...
16
votes
4answers
2k views

Why should XSS filters escape forward slash?

In OWASP recommendations regarding escaping untrusted input for HTML element content, they list the following: & --> &amp; < --> &lt; > --> &gt; " --> &quot; ' --...
8
votes
4answers
2k views

Escaping JavaScript constants

how can untrusted values be included in a html-page as javascript string constants? Although the case i am asking uses JSF and Rails, I think this is a general problem independent of the server side ...