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diff --git a/guides/source/security.md b/guides/source/security.md index 9d7fdb3c6d..7e39986f8b 100644 --- a/guides/source/security.md +++ b/guides/source/security.md @@ -17,7 +17,7 @@ After reading this guide, you will know: Introduction ------------ -Web application frameworks are made to help developers build web applications. Some of them also help you with securing the web application. In fact one framework is not more secure than another: If you use it correctly, you will be able to build secure apps with many frameworks. Ruby on Rails has some clever helper methods, for example against SQL injection, so that this is hardly a problem. It's nice to see that all of the Rails applications I audited had a good level of security. +Web application frameworks are made to help developers build web applications. Some of them also help you with securing the web application. In fact one framework is not more secure than another: If you use it correctly, you will be able to build secure apps with many frameworks. Ruby on Rails has some clever helper methods, for example against SQL injection, so that this is hardly a problem. In general there is no such thing as plug-n-play security. Security depends on the people using the framework, and sometimes on the development method. And it depends on all layers of a web application environment: The back-end storage, the web server and the web application itself (and possibly other layers or applications). @@ -25,7 +25,7 @@ The Gartner Group however estimates that 75% of attacks are at the web applicati The threats against web applications include user account hijacking, bypass of access control, reading or modifying sensitive data, or presenting fraudulent content. Or an attacker might be able to install a Trojan horse program or unsolicited e-mail sending software, aim at financial enrichment or cause brand name damage by modifying company resources. In order to prevent attacks, minimize their impact and remove points of attack, first of all, you have to fully understand the attack methods in order to find the correct countermeasures. That is what this guide aims at. -In order to develop secure web applications you have to keep up to date on all layers and know your enemies. To keep up to date subscribe to security mailing lists, read security blogs and make updating and security checks a habit (check the <a href="#additional-resources">Additional Resources</a> chapter). I do it manually because that's how you find the nasty logical security problems. +In order to develop secure web applications you have to keep up to date on all layers and know your enemies. To keep up to date subscribe to security mailing lists, read security blogs and make updating and security checks a habit (check the <a href="#additional-resources">Additional Resources</a> chapter). It is done manually because that's how you find the nasty logical security problems. Sessions -------- @@ -60,7 +60,7 @@ Many web applications have an authentication system: a user provides a user name Hence, the cookie serves as temporary authentication for the web application. Anyone who seizes a cookie from someone else, may use the web application as this user - with possibly severe consequences. Here are some ways to hijack a session, and their countermeasures: -* Sniff the cookie in an insecure network. A wireless LAN can be an example of such a network. In an unencrypted wireless LAN it is especially easy to listen to the traffic of all connected clients. This is one more reason not to work from a coffee shop. For the web application builder this means to _provide a secure connection over SSL_. In Rails 3.1 and later, this could be accomplished by always forcing SSL connection in your application config file: +* Sniff the cookie in an insecure network. A wireless LAN can be an example of such a network. In an unencrypted wireless LAN it is especially easy to listen to the traffic of all connected clients. For the web application builder this means to _provide a secure connection over SSL_. In Rails 3.1 and later, this could be accomplished by always forcing SSL connection in your application config file: ```ruby config.force_ssl = true @@ -135,8 +135,8 @@ NOTE: _Apart from stealing a user's session id, the attacker may fix a session i This attack focuses on fixing a user's session id known to the attacker, and forcing the user's browser into using this id. It is therefore not necessary for the attacker to steal the session id afterwards. Here is how this attack works: * The attacker creates a valid session id: They load the login page of the web application where they want to fix the session, and take the session id in the cookie from the response (see number 1 and 2 in the image). -* They possibly maintains the session. Expiring sessions, for example every 20 minutes, greatly reduces the time-frame for attack. Therefore they access the web application from time to time in order to keep the session alive. -* Now the attacker will force the user's browser into using this session id (see number 3 in the image). As you may not change a cookie of another domain (because of the same origin policy), the attacker has to run a JavaScript from the domain of the target web application. Injecting the JavaScript code into the application by XSS accomplishes this attack. Here is an example: `<script>document.cookie="_session_id=16d5b78abb28e3d6206b60f22a03c8d9";</script>`. Read more about XSS and injection later on. +* They maintain the session by accessing the web application periodically in order to keep an expiring session alive. +* The attacker forces the user's browser into using this session id (see number 3 in the image). As you may not change a cookie of another domain (because of the same origin policy), the attacker has to run a JavaScript from the domain of the target web application. Injecting the JavaScript code into the application by XSS accomplishes this attack. Here is an example: `<script>document.cookie="_session_id=16d5b78abb28e3d6206b60f22a03c8d9";</script>`. Read more about XSS and injection later on. * The attacker lures the victim to the infected page with the JavaScript code. By viewing the page, the victim's browser will change the session id to the trap session id. * As the new trap session is unused, the web application will require the user to authenticate. * From now on, the victim and the attacker will co-use the web application with the same session: The session became valid and the victim didn't notice the attack. @@ -198,7 +198,7 @@ In the <a href="#sessions">session chapter</a> you have learned that most Rails It is important to notice that the actual crafted image or link doesn't necessarily have to be situated in the web application's domain, it can be anywhere - in a forum, blog post or email. -CSRF appears very rarely in CVE (Common Vulnerabilities and Exposures) - less than 0.1% in 2006 - but it really is a 'sleeping giant' [Grossman]. This is in stark contrast to the results in my (and others) security contract work - _CSRF is an important security issue_. +CSRF appears very rarely in CVE (Common Vulnerabilities and Exposures) - less than 0.1% in 2006 - but it really is a 'sleeping giant' [Grossman]. This is in stark contrast to the results in many security contract works - _CSRF is an important security issue_. ### CSRF Countermeasures @@ -374,7 +374,7 @@ For _countermeasures against CSRF in administration interfaces and Intranet appl The common admin interface works like this: it's located at www.example.com/admin, may be accessed only if the admin flag is set in the User model, re-displays user input and allows the admin to delete/add/edit whatever data desired. Here are some thoughts about this: -* It is very important to _think about the worst case_: What if someone really got hold of my cookie or user credentials. You could _introduce roles_ for the admin interface to limit the possibilities of the attacker. Or how about _special login credentials_ for the admin interface, other than the ones used for the public part of the application. Or a _special password for very serious actions_? +* It is very important to _think about the worst case_: What if someone really got hold of your cookies or user credentials. You could _introduce roles_ for the admin interface to limit the possibilities of the attacker. Or how about _special login credentials_ for the admin interface, other than the ones used for the public part of the application. Or a _special password for very serious actions_? * Does the admin really have to access the interface from everywhere in the world? Think about _limiting the login to a bunch of source IP addresses_. Examine request.remote_ip to find out about the user's IP address. This is not bullet-proof, but a great barrier. Remember that there might be a proxy in use, though. @@ -406,7 +406,7 @@ If the parameter was nil, the resulting SQL query will be SELECT * FROM users WHERE (users.activation_code IS NULL) LIMIT 1 ``` -And thus it found the first user in the database, returned it and logged them in. You can find out more about it in [my blog post](http://www.rorsecurity.info/2007/10/28/restful_authentication-login-security/). _It is advisable to update your plug-ins from time to time_. Moreover, you can review your application to find more flaws like this. +And thus it found the first user in the database, returned it and logged them in. You can find out more about it in [this blog post](http://www.rorsecurity.info/2007/10/28/restful_authentication-login-security/). _It is advisable to update your plug-ins from time to time_. Moreover, you can review your application to find more flaws like this. ### Brute-Forcing Accounts @@ -732,7 +732,7 @@ Imagine a blacklist deletes "script" from the user input. Now the attacker injec strip_tags("some<<b>script>alert('hello')<</b>/script>") ``` -This returned "some<script>alert('hello')</script>", which makes an attack work. That's why I vote for a whitelist approach, using the updated Rails 2 method sanitize(): +This returned "some<script>alert('hello')</script>", which makes an attack work. That's why a whitelist approach is better, using the updated Rails 2 method sanitize(): ```ruby tags = %w(a acronym b strong i em li ul ol h1 h2 h3 h4 h5 h6 blockquote br cite sub sup ins p) @@ -741,7 +741,7 @@ s = sanitize(user_input, tags: tags, attributes: %w(href title)) This allows only the given tags and does a good job, even against all kinds of tricks and malformed tags. -As a second step, _it is good practice to escape all output of the application_, especially when re-displaying user input, which hasn't been input-filtered (as in the search form example earlier on). _Use `escapeHTML()` (or its alias `h()`) method_ to replace the HTML input characters &, ", <, > by their uninterpreted representations in HTML (`&`, `"`, `<`;, and `>`). However, it can easily happen that the programmer forgets to use it, so _it is recommended to use the [SafeErb](http://safe-erb.rubyforge.org/svn/plugins/safe_erb/) plugin_. SafeErb reminds you to escape strings from external sources. +As a second step, _it is good practice to escape all output of the application_, especially when re-displaying user input, which hasn't been input-filtered (as in the search form example earlier on). _Use `escapeHTML()` (or its alias `h()`) method_ to replace the HTML input characters &, ", <, > by their uninterpreted representations in HTML (`&`, `"`, `<`;, and `>`). However, it can easily happen that the programmer forgets to use it, so _it is recommended to use the SafeErb gem. SafeErb reminds you to escape strings from external sources. ##### Obfuscation and Encoding Injection @@ -812,7 +812,7 @@ The [moz-binding](http://www.securiteam.com/securitynews/5LP051FHPE.html) CSS pr #### Countermeasures -This example, again, showed that a blacklist filter is never complete. However, as custom CSS in web applications is a quite rare feature, I am not aware of a whitelist CSS filter. _If you want to allow custom colors or images, you can allow the user to choose them and build the CSS in the web application_. Use Rails' `sanitize()` method as a model for a whitelist CSS filter, if you really need one. +This example, again, showed that a blacklist filter is never complete. However, as custom CSS in web applications is a quite rare feature, it may be hard to find a good whitelist CSS filter. _If you want to allow custom colors or images, you can allow the user to choose them and build the CSS in the web application_. Use Rails' `sanitize()` method as a model for a whitelist CSS filter, if you really need one. ### Textile Injection |