The common name for the language used primarily for scripting in web browsers. It is not related to the Java language. Standardized as ECMAScript, its dialects/implementations include JavaScript and JScript.

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123
votes
3answers
17k views

This JavaScript code is injected on my hotel Wi-Fi: should I be worried?

While connected to my hotel Wi-Fi, visiting the URL http://www.google-analytics.com/ga.js results in the following content being served: var ga_exists; if(!ga_exists) { ga_exists = 1; var ...
68
votes
4answers
25k views

Why is the same origin policy so important?

I can't really fully understand what same origin domain means. I know it means that when getting a resource from another domain (say a JS file) it will run from the context of the domain that serves ...
59
votes
3answers
41k views

Securing a JavaScript Single Page App with RESTful backend

I'm currently in the process of building a JavaScript SPA and have been researching how to secure it. There is currently as RESTful API that is being completely interacted with through AJAX. We also ...
57
votes
6answers
9k 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 ...
50
votes
6answers
6k views

Does injecting querystring values directly into HTML pose a security risk?

Someone reported a bug on my site that I don't really consider an issue. My site has an URL akin to this: www.site.com/ajax/ads.asp?callback=[text injection] So filetype is application/json, and I ...
45
votes
3answers
4k views

I found obfuscated code in a comment on my blog. What should I do?

Today I was checking comments on my blog and I found a strange comment, here is the exact text <script>var ...
45
votes
3answers
4k views

For an end-user, is HTML5/JavaScript more secure than Flash?

I’m not talking about server-side security or even necessarily XSS vulnerabilities, as these are attacks on vulnerable services and do not use any pre-existing vulnerabilities on the client side to ...
41
votes
5answers
5k views

What's the danger of having some random, out of my control, JavaScript code running on my pages?

My website pages reference some JavaScript code from a third-party CDN (analytics, etc). So I don't control what code is there - the third party may change those scripts at any moment and introduce ...
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 ...
32
votes
4answers
30k views

How do you know your server has been compromised?

I recently helped a client who had their server hacked. The hackers added some PHP code into the header of the homepage redirecting the user to a porn website — but only if they came from Google. This ...
26
votes
7answers
4k views

How to replace SSL/TLS?

I have to make a website for a NGO (Non-Governmental Organization), and they have the minimal options from their provider, so they can't have SSL/TLS (barely only HTML/PHP/MySQL/JS) The data that ...
26
votes
9answers
2k views

Why do some people really hate security via client-side?

For instance, lets look at a common login system for a website HTTPS connection is made User submits credentials via POST Server-side code hashes the password and looks if it matches the user name ...
25
votes
2answers
3k views

Does browser 'view-source' mode avoid scripting attacks?

Let's say there's a URL www.badjs.com which is untrusted and may contain bad scripts. Intuitively, a view-source navigation to that URL does not execute any scripts so it should be safe. It would at ...
25
votes
2answers
6k views

JavaScript written only with brackets?

I once saw JavaScript code which was only written as multiple brackets (). Does anybody remember this kind of code? There was also an online converter to convert "normal" JS into this style of code. I ...
25
votes
3answers
3k views

NoScript: How to determine which sites/scripts to whitelist?

NoScript is a great plug-in, both for security and for ad blocking. However, I've found it's not always easy to figure out what scripts need to be permitted on certain pages, to be able to use the ...
21
votes
4answers
5k views

Suspicious JavaScript in website header

I am not sure if this is the correct place to ask a questions such as this, apologies if it isn't. I have found the below code in the header of one of my wordPress websites, I am pretty sure it is ...
21
votes
2answers
3k views

Can javascript execution from address bar cause any harm to client's machine?

Given the fact that modern browsers these days prohibit JavaScript from having access to any resources on the client's machine, does JavaScript execution from the address bar pose any threat at all to ...
20
votes
1answer
4k 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 ...
19
votes
2answers
889 views

What risks should I be aware of before allowing advertisements being placed on my website?

The thought of having a 3rd party send javascript, and images to end users seems to be a scary thought, but that is exactly what we are doing when I place advertisements onto my site. Does serving ...
19
votes
3answers
4k views

What are the risks of using a CDN to speed up my website? How do I avoid them?

Content Delivery Networks (CDNs) are well known to speed up the performance of a website, but they create the obvious security risks if someone were to change the code that resides on the CDN. What ...
18
votes
3answers
7k views

Can JavaScript be used to capture the user's screen?

Can JavaScript be used to capture the user’s screen? If so, is this functionality available in any JS framework? (I do not need code examples: I am mainly asking to form an opinion about the security ...
18
votes
4answers
7k views

Generate cryptographically strong pseudorandom numbers in Javascript?

Is there any good way to generate cryptographically strong pseudorandom (or true random) numbers in Javascript? The crucial requirement: if a.com's Javascript generates some random numbers, no one ...
17
votes
6answers
8k views

Preventing information disclosure from browser back button/history?

I have sensitive data that will be hosted on a website, and I would like to prevent the data from being exposed in this scenario: The primary user logs off the application, but does not close the ...
17
votes
4answers
11k views

Is WebGL a security concern?

Is WebGL a potential security problem due to the low level access it provides? For example, a web page can attempt to compile and run any shader source it wants. It seems that security would ...
17
votes
1answer
3k views

Best way to secure javascript front end/REST back end architecture web site?

I would like to build the following project: public REST API back end which can be accessed by any authenticated client. front end with static files in HTML/CSS/Javascript with Backbone.js jQuery ...
16
votes
3answers
2k views

What security risks does Firefox 19's built-in PDF reader (pdf.js) bring?

Firefox 19 ships with pdf.js as the default PDF reader. One of the main stated goals is to reduce the exposure of users to the often vulnerable Adobe PDF reader/plugin. So what new risks does pdf.js ...
15
votes
4answers
12k views

What does this javascript file do? Is this a virus?

While searching on Google I found a website that shows one set of content to the Google Bot and an other to users (by redirecting to a new domain), and also a very suspicious Javascript file. Maybe ...
15
votes
3answers
6k 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 ...
15
votes
3answers
1k views

How secure is aSSL (javascript)? Does it effectively mimic SSL?

Some of you may be familiar with the aSSL project, which uses AJAX/PHP to mimic the SSL protocol. It uses RSA 512 or 1024 for the keys, and AES for the actual data. It looks impressive to me in ...
15
votes
5answers
2k views

What can I do about TLS 1.0 javascript injection vulnerability on my server?

The recent article featured on slashdot http://www.theregister.co.uk/2011/09/19/beast_exploits_paypal_ssl/ says that connections secured with TLS 1.0 are susceptible to man-in-the-middle decryption ...
15
votes
6answers
15k views

How to scan Javascript for malicious code?

We're planning to give the possibility to write community-driven extensions in javascript for our public webapp and let people to customize their instances of the application. The problem is to ...
14
votes
4answers
4k views

What are the security issues with “eval()” in JavaScript?

Every time that someone mentions eval(), everyone says that there are "security issues" with it, but nobody ever goes into detail about what they are. Most modern browsers seem to be able to debug ...
14
votes
3answers
2k views

What bad coding practices makes a browser extension vulnerable?

I'm trying to scan JavaScript files for vulnerabilities using JSHint. Specifically, I'm scanning the JavaScript files of browser extensions. To look for possible vulnerabilities I'm looking for bad ...
14
votes
2answers
1k views

Does it make sense to hash a session id before passing it to an advertisement partner?

My company runs a webshop. We work with a partner that gives discount vouchers to our customers after they buy (the vouchers can be used in other online shops) and also gives vouchers for our shop to ...
14
votes
2answers
5k views

Cordova/Phonegap: RefreshToken in localstorage

I am (partly) following a tutorial to develop a cordova app, based on angularJS. The author stores the refresh token in local storage, which was said to be very bad practice in one of the comments on ...
13
votes
5answers
3k 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 ...
13
votes
2answers
466 views

Advertisement on Skype tried to download a file to my computer using Javascript

I usually have Skype running in the background. If you have ever used Skype before, you probably know it has advertisements. One of these advertisements made two windows pop up on my screen, asking to ...
12
votes
4answers
2k views

How do I protect myself from clickjacking attacks?

I've seen many friends getting clickjacked on Facebook and similar sites. How does one detect and prevent clickjacking? How should I teach my friends to do the same?
12
votes
4answers
1k views

How to step through malicious JavaScript?

There's a Facebook virus doing the rounds: Your face in 20 years (safe link, but don't follow the instructions). It clearly grabs some Javascript from a url (e.g. ...
12
votes
4answers
4k views

Challenging challenge: client-side password hashing and server-side password verification

We have a website where users need to log in to access privileged information. Obviously we are using SSL, but I also want to avoid plaintext passwords from accidently ending up in server logs, or ...
12
votes
5answers
8k views

How to validate if a JavaScript library is secure?

I'm the main developer for an Open Source JavaScript library. That library is used in the company I work for, for several clients. Every now and then there is a client that feels paranoid about ...
12
votes
2answers
626 views

What should I look for when auditing a Firefox extension / plugin?

I've been asked to do a security audit on a Firefox add-on developed by a third party. I am a web developer with a reasonable grasp of JavaScript but am not a browser security expert. What kinds of ...
12
votes
2answers
2k views

Where do I find JavaScript malware?

I am looking for JavaScript malware. I need it just for local tests on my computer for a project I am working on. Are there any Internet resources where I could find this?
11
votes
2answers
3k views

What does this injected code do?

One of my sites has just been hacked as this code has been inserted into random(?) files and places within the files. Does anyone understand what it is trying to do? I would welcome anything that may ...
11
votes
5answers
3k 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 ...
11
votes
3answers
1k views

Predicting Math.random() numbers?

I was reading up on the documentation for Math.random() and I found the note: Math.random() does not provide cryptographically secure random numbers. Do not use them for anything related to ...
11
votes
1answer
761 views

Why can't you steal the synchroniser token to do CSRF? [duplicate]

I'm reading up on CSRF and I came across synchroniser tokens. I don't understand why you can't do a CSRF to get the token to do a real CSRF. Example: bank.com has a form like this at ...
11
votes
3answers
1k views

Is there a particular security weakness from using server-side JavaScript?

I never used JavaScript server side, actually I didn't even know that it would be used or useful there. Now that I found out that it is possible and there is a quite active community, I am wondering ...
11
votes
5answers
2k views

Data needed for why not to load third party JavaScript on web page with credit card form

My company makes a JavaScript widget that e-commerce sites can embed on their pages. Our current instructions to our customers tell them to load our JS on every page of their site and most follow this ...
11
votes
1answer
2k views

Closing an HTML element without using literal slashes?

I'm investigating a vulnerability in an application that echoes a user-supplied filename without sanitizing the filename. E.g. a file named test-<script>alert("evil");.txt will result in that ...