An application that is accessed over a network such as the Internet or an intranet using a browser.

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29
votes
3answers
4k views

How long should an e-mail address confirmation link last and why must it expire at all?

After a user registers an e-mail is sent to them with a link they must click on to activate the account. I know other sites have a limit on the amount of time the user has to click the link, else the ...
29
votes
2answers
6k 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)....
29
votes
3answers
12k views

What useful things can I do with the html5 “keygen” element?

There's a new* keygen element in the html5 spec. It's supported in major browsers excepting Internet Explorer and Safari. Here's what it looks like: <form action="processkey.cgi" method="post" ...
28
votes
1answer
3k views

What cookie attacks are possible between computers in related DNS domains (*.example.com)?

Here, several servers in the same DNS domain emit cookies under a variety of settings (scope, HTTPS, Secure) and another host emits a cookie with the same value. Example Suppose a user has the ...
27
votes
3answers
6k views

Firebug appears to be decrypting SSL traffic: is it the correct behaviour?

In my company we were writing a small web application which would be hosted and tested under HSTS protocol. One of my tester complained that the username and password can be seen in cleartext so it ...
27
votes
5answers
23k views

What is the correct way to implement anti-CSRF form tokens?

I am fully aware of CSRF and have already implemented some safe forms, but I have never been happy with the results yet. I've created tokens as a md5 of username, form info and a salt and stored it ...
27
votes
5answers
2k views

How to improve as a security expert

I'm a professional software developer with a high interest in web application security. I'd say that I probably have a better understanding of the security of web applications than the average ...
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 ...
26
votes
7answers
3k views

Is it possible to modify your user agent http header for malicious use?

The Google crawl bot uses the user agent "Googlebot", and I am wondering if this knowledge can be used maliciously. Let's say in a random website, the Googlebot user agent is allowed to access an ...
26
votes
5answers
4k views

Security of an initial redirection from http://example.com to https://example.com

Suppose that http://example.com/<foo> systematically redirects to https://example.com/<foo>. I enter http://example.com in my browser's URL bar, and I see a page load and the URL bar now ...
25
votes
4answers
7k views

Should I block the Yandex Bot?

I have a web application that the Yandex spider is trying access into back-end a few times. After these spider searching, there are few Russian IP addresses that try to access back-end too and they ...
25
votes
8answers
24k views

Why do people still use/recommend MD5 if it is cracked since 1996?

It's still commonly recommended way of hashing passwords, even if it's insecurity had been proven in 1996 Therefore we suggest that in the future MD5 should no longer be implemented in ...
25
votes
1answer
25k views

What key exchange mechanism should be used in TLS?

There are many key exchange mechanisms that can be used in TLS. Among them are RSA, ECDH_ECDSA, ECDHE_ECDSA, ECDH_RSA, ECDHE_RSA and others. Which of these are more cryptographically secure and can be ...
24
votes
11answers
18k views

Prevent my site from being copied

Is it possible to protect my site from HTTrack Website Copier or any similar program? Without setting a max number of HTTP request from users.
24
votes
3answers
7k views

Why is it insecure to store the session ID in a cookie directly?

I am learning about session middleware. You have to supply a secret or the middleware complains: app.use(session({ secret: "abc", resave: false, saveUninitialized: false, store: new ...
24
votes
2answers
3k views

Is the undesirable conversion of a scientific number a vulnerability?

I noticed in several penetration tests that PHP is converting values like 1e9 to 1000000000 while the max accepted string length of this number is 3 (in the database storage and as maxlength property ...
24
votes
1answer
1k views

HTTP HEAD and its security versus operational uses

Most security advice I see recommends turning off HTTP Methods like TRACE, OPTIONS, HEAD etc. So now I have turned off most of these options on my web server and leaving only GET and POST options that ...
24
votes
5answers
7k views

What are the security risks of letting the users upload content to my site?

As a web designer (not a security expert) I wonder: If I allow users to upload content to my website (videos, images and text files), what are the real risks involved?
24
votes
2answers
5k views

Guidance for implementors of HTTPS-only sites (Server side)

The recent trend in HTTPS attacks is to attack the HTTP protocol. What should I do to increase my site's security if the only protocol I want is HTTPS? Some easy to implement ideas are Implement ...
23
votes
3answers
5k views

What are the disadvantages of implementing HTTP authentication in a web application? [duplicate]

I know that there are different types of authentication mechanisms available. One among them is the HTTP authentication. What is the danger in using this method compared to other methods?
23
votes
3answers
3k views

Should I have a maximum password length?

I'm creating a webapp, and part of my authentication method is password length. Should I put one in place? (say, 50 characters?) Or should I just put a minimum length (Currently at 6). Are there ...
23
votes
4answers
12k views

avoid hitting DB to authenticate a user on EVERY request in stateless web app architecture?

Summary Once a user logs into a web site and his username/password credentials are verified and an active session is established, is it possible to avoid hitting the DB for each and every request ...
23
votes
7answers
1k views

How can I protect a WordPress installation?

How do you go about protecting a default WordPress installation? What checklist do you use, best practices, tips and tricks, etc? Any recommendations on plugins, third-party tools are welcome.
22
votes
4answers
12k views

Should sensitive data ever be passed in the query string?

Should sensitive data ever be passed via the query string as opposed to the postback? I realize that the query string will be encrypted, but are there other reasons to avoid passing data in the ...
22
votes
7answers
7k views

What are some good website security scanning solutions?

What are some good web-based website security scanning solutions? I'm not too concerned if they are web-based solutions, or software that can be run locally. Generally, I'm looking for something we ...
22
votes
8answers
1k views

How to protect against brute forcing

How do you properly implement defenses against brute forcing? Is it best to store how many times someone tried to log in and block them after X attempts? And how would "someone" be identified? With ...
22
votes
4answers
2k views

How does using OpenID affect webapp security?

Using OpenID for authenticating users grows in popularity and, in fact, makes a webapp easier to use. But what are the security considerations one should bear in mind when deciding whether to ...
22
votes
2answers
8k views

What are the best practices for hardening a php.ini file?

In order to secure a PHP installation, what are the best settings for a php.ini file? What is absolutely vital in terms of security? What is recommended for most use cases?
21
votes
4answers
4k views

Keylogger web application protection

I'm trying to improve security in a web application. The application has an admin site and keyloggers are a concern that I'm trying to solve. Can the application do something that can prevent ...
21
votes
4answers
9k views

Why users want to disable cookies?

I just started to create a new web application. In the documentation, it is written that I have to prepare for the situation where users have disabled cookies. This is not the first time I have read ...
21
votes
6answers
61k views

Testing for HTTP TRACE method

How can I test for HTTP TRACE on my web-server? I need to train a Tester how to verify that the HTTP TRACE method is disabled. Ideally I need a script to paste into Firebug to initiate a https ...
21
votes
9answers
4k views

Is a web application firewall necessary if the application is secure?

Recently I've been reading about Web application firewalls and the fact that they protect against most frequent attacks like injections, XSS or CSRF. However, a good application should already be ...
21
votes
5answers
2k views

Why do some websites and programs restrict password characteristics?

There are some websites and even programs that I use that have rediculous password restrictions. Lots of forums for instance restrict passwords to ~32 characters. Others enforce a restricted charset. ...
21
votes
5answers
29k views

How can I find subdomains of a site?

One of the things I need to do from time to time is to find subdomains of a site for example. Starting with example.com sub1.example.com other.example.com another.example.com I'm ...
21
votes
4answers
23k views

How to hijack a session?

Despite the blatant title of the question, this is actually for a genuine purpose. My site uses PHP code like this: $select="select id from tableA where user_id='".$_SESSION['sess_user_id']."'"; ...
21
votes
3answers
2k views

Pitfalls of using OAuth for mobile Applications

OAuth is a popular authorization solution for web applications and mobile applications. What the pitfalls of using OAuth are in those two scenarios (as a web application providing OAuth access to my ...
20
votes
14answers
3k views

How can you become a competent web application security expert without breaking the law?

This question was asked here on Programmers Exchange, but it was suggested I ask here as well since most of the experts would likely hang out on IT Security exchange instead. I find this to be ...
20
votes
2answers
2k views

From a technical standpoint, how does the zero-day Internet Explorer vulnerability discovered in September 2012 work?

I'm looking for an answer that explains the issue from the prespective of a developer/engineer. What is exactly being exploited and why does it work? Please note that I am not looking for ...
20
votes
4answers
8k views

Is $_SERVER[ ] a safe source of data in PHP?

Can I 100% rely on $_SERVER[] to be a safe source of data that I do not need to sanitized like I do $_GET[] and $_POST[]?
20
votes
2answers
844 views

How is “<scrscriptipt>” or “selselectect” used to avoid filtering?

A technique for avoid filtering of common words is the one I described in the title. However, why does this technique work? SELECT isn't the same as SELSELECTECT for example.
20
votes
4answers
20k views

Is “Why Should You Avoid AES In MySQL?” true?

From a 2012 Smashing Magazine article quite a bold statement is made to avoid AES in MySQL itself. Or as they put it "Why Should You Avoid AES In MySQL?". However, if you search for SQL encryption, ...
20
votes
2answers
4k views

Which HTTP status codes are interesting from a security point of view?

I'm looking to extract interesting information from webserver logs and I wonder which HTTP status codes should I filter out? For example, 200 hits can be considered to be 'regular behavior' whereas ...
20
votes
5answers
4k views

Should I use Suhosin for PHP?

Suhosin can be used to increase the security of your PHP application. I can really see the use of it when you are using shared hosts, with multiple (possibly evil) people running their PHP apps there. ...
20
votes
2answers
918 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
5answers
2k views

From a security standpoint should users be asked to confirm their password when registering?

Is it advisable to have users re-type their password to confirm it's correct? On User Experience the general consensus seems to be no but I'm wondering if this has security ramifications? EDIT: my ...
19
votes
4answers
987 views

Should I be concerned when a “Forgot Password?” tool sends my password in plaintext?

Some sites I have been a member of in the past don't go through the normal "Forgot Password?" process. Instead of e-mailing me a unique password reset link or something of the like, I have received ...
19
votes
2answers
7k views

JavaScript Injection using Man in the Middle Attack

Suppose I am connected to a wifi-hotspot hosted by a malicious attacker. Further, suppose that I am accessing a login page of an fictitious email site tmail.com over insecure HTTP connection. My ...
19
votes
3answers
36k views

How to ensure that cookies are always sent via SSL when using ASP.NET on IIS 7.5?

Firesheep has brought the issue of insecure cookie exchanges to the forefront. How can you ensure that all cookie exchanges are forced to occur only via an SSL-secured connection to the server when ...
19
votes
3answers
8k views

Security risks with JSONP?

What are the security risks with JSONP? Is using JSONP in a new web application reasonable, from a security perspective, or is it better to use a different method for cross-origin web mashups? If ...
19
votes
1answer
3k views

The “.htaccess” file can be downloaded. Why? How to fix?

Maybe a noob question. I've tried searching but maybe my search terms were too specific. I've just conducted a pen test on a client's site. The site allowed me to download .htaccess just by simply ...