Questions tagged [html]

HTML (HyperText Markup Language) is a language used to create web pages using tags inline with the content to indicate to browsers how to display that content, using the tags to interpret formatting, images, scripts and other content.

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106
votes
5answers
56k views

Should websites be allowed to disable autocomplete on forms or fields?

Currently, there is an HTML form/input attribute called autocomplete, which, when set to off, disables autocomplete/autofill for that form or element. Some banks seem to use this to prevent password ...
86
votes
8answers
67k 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 ...
64
votes
2answers
8k views

Are EU cookie consent forms safe? [closed]

Does the EU consent form system pose a new security risk? Today we have to click OK on about 20 cookie consent forms every week, where previously we could mostly dismiss internet forms as being ...
61
votes
1answer
4k views

“Allow __ to be fullscreen?”

I have been asking myself for a while what's the purpose of that popup showing up in pretty much all the modern browsers upon entering the full-screen mode of a video or website. It appears to be a ...
60
votes
6answers
10k views

Anonymous surveys that aren't so anonymous

In the past I have completed an 'anonymous' survey at work only to find that my employer was able to garner a lot of not-anonymous information from this survey. Location, name of manager, etc. None ...
44
votes
8answers
12k views

Is it ever safe to open a suspicious HTML file (e.g. email attachment)?

If I receive an email that has an attachment called something like safe-link.html would it ever be safe to open this file? Clearly, HTML files may have malicious scripts embedded that could run when ...
40
votes
7answers
8k views

Security risks of user generated HTML?

I am creating a website that allows people to upload HTML content. Currently these are the tags that are banned: <script></script> <iframe> <object> <embed> <style&...
40
votes
4answers
6k views

Have computer criminals been known to exploit easily-edited websites like Wikipedia to embed malicious scripts?

When I was reading a page on Wikipedia several months ago (December 2014) I saw what looked like a pop-up window from BT, but I soon realized that when I closed the page the pop-up disappeared. I then ...
30
votes
2answers
9k views

Important data can be modified from the developer console. What should I do?

Scenario: I have a to-do list that is generated with JavaScript using JSON that was encoded on the server side. I put the todo item id in the HTML id attribute. So the process goes like this: Server ...
28
votes
2answers
10k views

Why is “hovering over” a link in an email considered safe? Or is it harmful?

We are using a browser based email client and the email content is in HTML. One of my employers told us that if we receive a suspicious email with links, we have to hover over the link (to check ...
24
votes
2answers
3k views

Is there a way to make the browser remove the login-password from it's memory immediately, like Chrome seems to do on accounts.google.com?

I did some testing, and found that a memory dump of Chrome doesn't hold the password of gmail.com/Google after logging in to that site (the login happens on accounts.google.com). (My System is ...
23
votes
12answers
13k views

Is there a way to hide HTML source code yet keeping it effective?

I have a website with a client-side HTML contact form created manually (not as output of an HTML constructor like PHP): <form action="mailto:someone@example.com"> Email Adress:<br> ...
22
votes
2answers
2k views

Does this CSS code expose if a message is read, and how long they have been reading it?

This email analytics company offers an 'engagement metric' that shows how much time someone spends looking at an email, whether the email is printed or deleted. They also claim it works in pretty ...
20
votes
2answers
57k views

How to launch XSS code from an INPUT HTML tag upon page load?

Say I have the a website with the following code on it: <input type="text" id="search-text" name="query" value="?" /> Double quotes aren't escaped so I can break out of the value attribute, ...
17
votes
3answers
3k views

What does a HTML filter need to do, to protect against SVG attacks?

I recently learned that SVG (Scalable Vector Graphics) images introduce a number of opportunities for subtle attacks on the web. (See paper below.) While SVG images may look like an image, the file ...
16
votes
2answers
4k views

Why is CSP needed to protect against img-src leak?

GitHub explains the problem with img-src in "GitHub's post-CSP journey": A tag with an unclosed quote will capture all output up to the next matching quote. This could include security sensitive ...
16
votes
2answers
6k views

Attack Vectors for Purely Static Website (HTML and CSS)

I am sorry if this is a too trivial question, but once I was told that only a fool is sure of anything: as I am not sure about this question, I am willing to risk my neck by asking it anyway, all in ...
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; ' --...
14
votes
1answer
2k views

How can I embed iframe securely without restricting its functionality?

I'd want to embed an iframe from untrusted site into web application. Iframe: should be able to run Javascript and browser plugins (Flash, etc.) should not be able to access my web application ...
13
votes
3answers
9k views

Is there a way to bypass Django's XSS escaping with “unicode”?

Django (the Python web framework) escapes output to prevent XSS (Cross Site Scripting) attacks. It replaces ', ", <, >, & with their HTML safe versions. However this presentation on slide ...
12
votes
3answers
13k views

Content-Security-Policy hash of script

<?php header("Content-Security-Policy: default-src 'sha256-".base64_encode(hash('sha256', 'console.log("Hello world");', true))."'"); ?> <script>console.log("Hello world");</script> ...
11
votes
2answers
2k views

How do the Stack Exchange sites protect themselves from XSS? [duplicate]

It seems to me that because Users can post questions and comments in them with HTML markup (possibly <script> tags), Stack Exchange sites would be very exposed to XSS attacks. How do they ...
11
votes
2answers
4k views

Why shouldn't I put user input in HTML comments?

The OWASP XSS Prevention Cheat Sheet has a list of locations where untrusted data should never be put: <script>...NEVER PUT UNTRUSTED DATA HERE...</script> directly in a script <!-...
11
votes
1answer
969 views

Why is a “tainted canvas” a risk?

I understand the concern about a tainted canvas - the idea that the bits of an image from another site can be sent back to a malicious server. But can you explain the details of how exactly this works?...
10
votes
3answers
5k views

Allowing users to input a safe subset of HTML

I recently posted this question on Code Review and it was recommended that I ask you guys about it. Basically, this will be used to allow users to generate formatted content. It gets put inside of ...
10
votes
1answer
1k views

Should Content in <noscript> Blocks Be Escaped

The title pretty much says it all. It seems counter-intuitive to escape inside a <noscript> block because any js that an attacker is able to inject there shouldn't be executed. But, I'm still ...
9
votes
2answers
5k views

Escaping rich text editor output

When having a rich text editor on a web application, what is the best way to escape HTML entities and prevent XSS attacks but keep the formatting (<b>, <i>, <u>, ...etc.) ?
9
votes
1answer
3k views

What are the benefits and drawbacks of the HTML5 Keygen element?

As of January 2013, what are the potential benefits and drawbacks of the HTML5 Keygen element?
9
votes
2answers
300 views

Pitfalls when rolling your own “show password” functionality

I'm considering emulating the "Show password" functionality, available in some newer browsers, on a website, essentially as a polyfill for browsers which don't. The common way to do this is to call a ...
9
votes
2answers
16k views

Why are scripts injected through innerHTML not executed whilst onerror and other on<event> attributes on elements are? - Google XSS Challenge 2

SPOILER ALERT : Do not continue if you do not want to be spoiled I am currently doing the Google XSS Challenge Level 2 . I am injecting XSS code that is inserted into the document using element....
9
votes
1answer
2k views

Why is sub resource integrity (SRI) only limited to certain files?

I'm quite enthusiastic about the Sub resource integrity (SRI) features. But, why is it only limited to JS and CSS files? I tried to pin a LESS (CSS variant) file, of which the integrity tag was ...
9
votes
2answers
1k views

Best practices when forwarding an email or copy / pasting from confidential information sources?

I get asked this a lot from older people, or for legal matters. They want to forward an email message they've received to another party, while removing any identifying information from the first party ...
9
votes
1answer
2k views

How do I securely embed an <img> tag using a user-given URL?

If I hypothetically wanted to allow users to use an avatar from an arbitrary URL like this: <img class="avatar" src="{user input}" /> There are many problems that I can think of: There are ...
9
votes
3answers
2k views

Any eventhandlers that apply to hidden elements?

I'm trying to XSS a search field and my attack vector is getting reflected like this: <input type="text" id="txtRpHiddenKeyword" style="display: none;" value="ATTACK VECTOR HERE" /> Only ...
9
votes
2answers
2k views

Drupal filters XSS with regexes. What could bypass it?

Drupal filters HTML strings against XSS attacks using regexes: http://api.drupal.org/api/drupal/includes%21common.inc/function/filter_xss/7 However, as a lot of people know, HTML can't be parsed with ...
8
votes
2answers
2k views

Is it sufficient to convert ', < and > to avoid XSS in JavaScript strings?

Is it sufficient to convert ' to &#039; , > to &gt; and < to &lt; to avoid XSS when inserting untrusted data into a JavaScript string as below? <script> param='payload'; </...
8
votes
3answers
6k views

HTML broken and comments inserted in website

One of our customer's site turned into a broken state. Most of the content (which is in Japanese), turned something like this: 会�����案内 (which originally was: 会社案内. Checking on the code, there is no ...
8
votes
3answers
2k views

Is a HTML form tag more exploitable than a HTML link in user submitted content?

I have a content editor in a web application which allows administrators to add and edit content in certain areas of the application. The editor component I have used automatically removes any script ...
7
votes
4answers
12k views

Is it possible to make an xss with only html tags

I'm not aware of all the xss tricks.. While programming in Ruby on Rails, using a sanitize method to allow only certain tags and it makes its best to clear all the other tags and scripts the ...
7
votes
6answers
2k views

Cleartext password in HTML

Is there any problem with outputing a user's password to the HTML in an hidden field (see use case below before flaming xD)? The use case is a registration form with two steps. The user fills in the ...
7
votes
5answers
9k views

Is converting `<` to `&lt;` sufficient to prevent execution of JavaScript from arbitrary HTML?

This is kind of a bar-bet question. An acquaintance of mine has made the claim that, given an arbitrary glob of HTML, it can be completely prevented from executing JavaScript if, before slapping it ...
7
votes
4answers
26k views

how can you inject malicious code into an innocent-looking URL?

I am learning about XSS attacks. Wikipedia says that in a non-persistent attack an attacker may provide an innocent-looking URL that "points to a trusted site but actually has an XSS vector." What ...
7
votes
1answer
3k views

What possible use does an iFrame have for security?

I'm looking at code for an old login form I'm redesigning. It's a simple table with two input fields for username and password. But just before the end </table> tag there's a blank iFrame which ...
7
votes
4answers
2k views

How come <img> calls do not violate the Same Origin Policy?

I'm a bit confused regarding the subject of Same Origin Policy (SOP). If I understand correctly, the purpose of the SOP is to prevent one page from obtaining access to sensitive data on another web ...
7
votes
4answers
425 views

Limited JavaScript app scenario: Attack vectors and mitigation

I'm going to be developing a single page JavaScript app which allows input via a textarea. This input is never sent to the server, never shown to another user, and will only be persisted in browser ...
7
votes
2answers
1k views

Workarounds for :visited CSS History reconnaissance

Several years ago it was possible to use a:visited { background: url('/log.php'); } to figure out on what website user has been previously. But now it is restricted by browsers. Is there any ...
7
votes
1answer
358 views

Can an attacker force a browser to use quirks mode to render a page?

During a pentest, I've found a potential vulnerability on a web page, but it can only be exploited in quirks mode. The page starts with <!doctype html>, which triggers standards mode so at ...
7
votes
1answer
1k views

Safe to render data directly to DOM from localStorage? XSS attack possible?

I read that localstorage is susceptible to XSS attacks. I currently store JSON Web Token (JWT) in localstorage, and I access and display data about the user through localstorage: var localstore = //...
6
votes
5answers
2k views

HTML Entities to hide Email Addresses

I'm on WordPress trying to keep spambots from grabbing email addresses that may be in The Content. WordPress has a nifty little function simply called antispambot() which will convert the email ...
6
votes
1answer
2k views

Does Strict-Transport Security Header (HSTS) need to be applied to non 200 response pages (e.g. 403, 302)

I have an application that is protected by Cloudflare. The application responds with a HSTS on all of the other pages except HTTP status 403 Forbidden and 302 Moved Temporarily. It seems to be ...

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