diff options
Diffstat (limited to 'railties/guides')
| -rw-r--r-- | railties/guides/source/security.textile | 55 |
1 files changed, 27 insertions, 28 deletions
diff --git a/railties/guides/source/security.textile b/railties/guides/source/security.textile index 98a42f1223..adb96fa19c 100644 --- a/railties/guides/source/security.textile +++ b/railties/guides/source/security.textile @@ -29,7 +29,7 @@ h3. Sessions A good place to start looking at security is with sessions, which can be vulnerable to particular attacks. -h4. What are sessions? +h4. What are Sessions? -- _HTTP is a stateless protocol. Sessions make it stateful._ @@ -49,7 +49,7 @@ h4. Session id A session id consists of the hash value of a random string. The random string is the current time, a random number between 0 and 1, the process id number of the Ruby interpreter (also basically a random number) and a constant string. Currently it is not feasible to brute-force Rails' session ids. To date MD5 is uncompromised, but there have been collisions, so it is theoretically possible to create another input text with the same hash value. But this has had no security impact to date. -h4. Session hijacking +h4. Session Hijacking -- _Stealing a user's session id lets an attacker use the web application in the victim's name._ @@ -67,7 +67,7 @@ Hence, the cookie serves as temporary authentication for the web application. Ev The main objective of most attackers is to make money. The underground prices for stolen bank login accounts range from $10–$1000 (depending on the available amount of funds), $0.40–$20 for credit card numbers, $1–$8 for online auction site accounts and $4–$30 for email passwords, according to the "Symantec Global Internet Security Threat Report":http://eval.symantec.com/mktginfo/enterprise/white_papers/b-whitepaper_internet_security_threat_report_xiii_04-2008.en-us.pdf. -h4. Session guidelines +h4. Session Guidelines -- _Here are some general guidelines on sessions._ @@ -77,7 +77,7 @@ This will also be a good idea, if you modify the structure of an object and old * _(highlight)Critical data should not be stored in session_. If the user clears his cookies or closes the browser, they will be lost. And with a client-side session storage, the user can read the data. -h4. Session storage +h4. Session Storage -- _Rails provides several storage mechanisms for the session hashes. The most important are ActiveRecordStore and CookieStore._ @@ -100,7 +100,7 @@ config.action_controller.session = { There are, however, derivatives of CookieStore which encrypt the session hash, so the client cannot see it. -h4. Replay attacks for CookieStore sessions +h4. Replay Attacks for CookieStore Sessions -- _Another sort of attack you have to be aware of when using CookieStore is the replay attack._ @@ -116,7 +116,7 @@ Including a nonce (a random value) in the session solves replay attacks. A nonce The best _(highlight)solution against it is not to store this kind of data in a session, but in the database_. In this case store the credit in the database and the logged_in_user_id in the session. -h4. Session fixation +h4. Session Fixation -- _Apart from stealing a user's session id, the attacker may fix a session id known to him. This is called session fixation._ @@ -131,7 +131,7 @@ This attack focuses on fixing a user's session id known to the attacker, and for # 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. -h4. Session fixation – Countermeasures +h4. Session Fixation – Countermeasures -- _One line of code will protect you from session fixation._ @@ -145,7 +145,7 @@ If you use the popular RestfulAuthentication plugin for user management, add res Another countermeasure is to _(highlight)save user-specific properties in the session_, verify them every time a request comes in, and deny access, if the information does not match. Such properties could be the remote IP address or the user agent (the web browser name), though the latter is less user-specific. When saving the IP address, you have to bear in mind that there are Internet service providers or large organizations that put their users behind proxies. _(highlight)These might change over the course of a session_, so these users will not be able to use your application, or only in a limited way. -h4. Session expiry +h4. Session Expiry -- _Sessions that never expire extend the time-frame for attacks such as cross-site reference forgery (CSRF), session hijacking and session fixation._ @@ -172,7 +172,7 @@ self.delete_all "updated_at < '#{time.to_s(:db)}' OR created_at < '#{2.days.ago.to_s(:db)}'" </ruby> -h3. Cross-Site Reference Forgery (CSRF) +h3. Cross-Site Request Forgery (CSRF) -- _This attack method works by including malicious code or a link in a page that accesses a web application that the user is believed to have authenticated. If the session for that web application has not timed out, an attacker may execute unauthorized commands._ @@ -278,7 +278,7 @@ Another redirection and self-contained XSS attack works in Firefox and Opera by This example is a Base64 encoded JavaScript which displays a simple message box. In a redirection URL, an attacker could redirect to this URL with the malicious code in it. As a countermeasure, _(highlight)do not allow the user to supply (parts of) the URL to be redirected to_. -h4. File uploads +h4. File Uploads -- _Make sure file uploads don't overwrite important files, and process media files asynchronously._ @@ -303,7 +303,7 @@ A significant disadvantage of synchronous processing of file uploads (as the att The solution to this is best to _(highlight)process media files asynchronously_: Save the media file and schedule a processing request in the database. A second process will handle the processing of the file in the background. -h4. Executable code in file uploads +h4. Executable Code in File Uploads -- _Source code in uploaded files may be executed when placed in specific directories. Do not place file uploads in Rails' /public directory if it is Apache's home directory._ @@ -311,7 +311,7 @@ The popular Apache web server has an option called DocumentRoot. This is the hom _(highlight)If your Apache DocumentRoot points to Rails' /public directory, do not put file uploads in it_, store files at least one level downwards. -h4. File downloads +h4. File Downloads -- _Make sure users cannot download arbitrary files._ @@ -333,7 +333,7 @@ send_file filename, :disposition => 'inline' Another (additional) approach is to store the file names in the database and name the files on the disk after the ids in the database. This is also a good approach to avoid possible code in an uploaded file to be executed. The attachment_fu plugin does this in a similar way. -h3. Intranet and Admin security +h3. Intranet and Admin Security -- _Intranet and administration interfaces are popular attack targets, because they allow privileged access. Although this would require several extra-security measures, the opposite is the case in the real world._ @@ -355,7 +355,7 @@ Another popular attack is to spam your web application, your blog or forum to pr For _(highlight)countermeasures against CSRF in administration interfaces and Intranet applications, refer to the countermeasures in the CSRF section_. -h4. Additional precautions +h4. Additional Precautions 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: @@ -365,7 +365,7 @@ The common admin interface works like this: it's located at www.example.com/admi * _(highlight)Put the admin interface to a special sub-domain_ such as admin.application.com and make it a separate application with its own user management. This makes stealing an admin cookie from the usual domain, www.application.com, impossible. This is because of the same origin policy in your browser: An injected (XSS) script on www.application.com may not read the cookie for admin.application.com and vice-versa. -h3. Mass assignment +h3. Mass Assignment -- _Without any precautions Model.new(params[:model]) allows attackers to set any database column's value._ @@ -440,7 +440,7 @@ ActiveRecord::Base.send(:attr_accessible, nil) This will create an empty whitelist of attributes available for mass assignment for all models in your app. As such, your models will need to explicitly whitelist accessible parameters by using an +attr_accessible+ declaration. This technique is best applied at the start of a new project. However, for an existing project with a thorough set of functional tests, it should be straightforward and relatively quick to insert this initializer, run your tests, and expose each attribute (via +attr_accessible+) as dictated by your failing tests. -h3. User management +h3. User Management -- _Almost every web application has to deal with authorization and authentication. Instead of rolling your own, it is advisable to use common plug-ins. But keep them up-to-date, too. A few additional precautions can make your application even more secure._ @@ -467,7 +467,7 @@ 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 him in. You can find out more about it in "my blog post":http://www.rorsecurity.info/2007/10/28/restful_authentication-login-security/. _(highlight)It is advisable to update your plug-ins from time to time_. Moreover, you can review your application to find more flaws like this. -h4. Brute-forcing accounts +h4. Brute-Forcing Accounts -- _Brute-force attacks on accounts are trial and error attacks on the login credentials. Fend them off with more generic error messages and possibly require to enter a CAPTCHA._ @@ -479,7 +479,7 @@ However, what most web application designers neglect, are the forgot-password pa In order to mitigate such attacks, _(highlight)display a generic error message on forgot-password pages, too_. Moreover, you can _(highlight)require to enter a CAPTCHA after a number of failed logins from a certain IP address_. Note, however, that this is not a bullet-proof solution against automatic programs, because these programs may change their IP address exactly as often. However, it raises the barrier of an attack. -h4. Account hijacking +h4. Account Hijacking -- _Many web applications make it easy to hijack user accounts. Why not be different and make it more difficult?_ @@ -532,7 +532,7 @@ By default, Rails logs all requests being made to the web application. But log f filter_parameter_logging :password </ruby> -h4. Good passwords +h4. Good Passwords -- _Do you find it hard to remember all your passwords? Don't write them down, but use the initial letters of each word in an easy to remember sentence._ @@ -544,7 +544,7 @@ It is interesting that only 4% of these passwords were dictionary words and the A good password is a long alphanumeric combination of mixed cases. As this is quite hard to remember, it is advisable to enter only the _(highlight)first letters of a sentence that you can easily remember_. For example "The quick brown fox jumps over the lazy dog" will be "Tqbfjotld". Note that this is just an example, you should not use well known phrases like these, as they might appear in cracker dictionaries, too. -h4. Regular expressions +h4. Regular Expressions -- _A common pitfall in Ruby's regular expressions is to match the string's beginning and end by ^ and $, instead of \A and \z._ @@ -568,7 +568,7 @@ Whereas %0A is a line feed in URL encoding, so Rails automatically converts it t /\A[\w\.\-\+]+\z/ </ruby> -h4. Privilege escalation +h4. Privilege Escalation -- _Changing a single parameter may give the user unauthorized access. Remember that every parameter may be changed, no matter how much you hide or obfuscate it._ @@ -629,7 +629,7 @@ SELECT * FROM projects WHERE name = '' OR 1 --' The two dashes start a comment ignoring everything after it. So the query returns all records from the projects table including those blind to the user. This is because the condition is true for all records. -h5. Bypassing authorization +h5. Bypassing Authorization Usually a web application includes access control. The user enters his login credentials, the web applications tries to find the matching record in the users table. The application grants access when it finds a record. However, an attacker may possibly bypass this check with SQL injection. The following shows a typical database query in Rails to find the first record in the users table which matches the login credentials parameters supplied by the user. @@ -645,7 +645,7 @@ SELECT * FROM users WHERE login = '' OR '1'='1' AND password = '' OR '2'>'1' This will simply find the first record in the database, and grants access to this user. -h5. Unauthorized reading +h5. Unauthorized Reading The UNION statement connects two SQL queries and returns the data in one set. An attacker can use it to read arbitrary data from the database. Let's take the example from above: @@ -692,7 +692,7 @@ h4. Cross-Site Scripting (XSS) -- _The most widespread, and one of the most devastating security vulnerabilities in web applications is XSS. This malicious attack injects client-side executable code. Rails provides helper methods to fend these attacks off._ -h5. Entry points +h5. Entry Points An entry point is a vulnerable URL and its parameters where an attacker can start an attack. @@ -721,7 +721,7 @@ This JavaScript code will simply display an alert box. The next examples do exac <table background="javascript:alert('Hello')"> </html> -h6. Cookie theft +h6. Cookie Theft These examples don't do any harm so far, so let's see how an attacker can steal the user's cookie (and thus hijack the user's session). In JavaScript you can use the document.cookie property to read and write the document's cookie. JavaScript enforces the same origin policy, that means a script from one domain cannot access cookies of another domain. The document.cookie property holds the cookie of the originating web server. However, you can read and write this property, if you embed the code directly in the HTML document (as it happens with XSS). Inject this anywhere in your web application to see your own cookie on the result page: @@ -796,7 +796,7 @@ Network traffic is mostly based on the limited Western alphabet, so new characte This example pops up a message box. It will be recognized by the above sanitize() filter, though. A great tool to obfuscate and encode strings, and thus “get to know your enemy”, is the "Hackvertor":http://www.businessinfo.co.uk/labs/hackvertor/hackvertor.php. Rails‘ sanitize() method does a good job to fend off encoding attacks. -h5. Examples from the underground +h5. Examples from the Underground _In order to understand today's attacks on web applications, it's best to take a look at some real-world attack vectors._ @@ -862,7 +862,6 @@ h4. Textile Injection For example, RedCloth translates +_test_+ to <em>test<em>, which makes the text italic. However, up to the current version 3.0.4, it is still vulnerable to XSS. Get the "all-new version 4":http://www.redcloth.org that removed serious bugs. However, even that version has "some security bugs":http://www.rorsecurity.info/journal/2008/10/13/new-redcloth-security.html, so the countermeasures still apply. Here is an example for version 3.0.4: - <ruby> RedCloth.new('<script>alert(1)</script>').to_html # => "<script>alert(1)</script>" @@ -971,7 +970,7 @@ Content-Type: text/html Under certain circumstances this would present the malicious HTML to the victim. However, this seems to work with Keep-Alive connections, only (and many browsers are using one-time connections). But you can't rely on this. _(highlight)In any case this is a serious bug, and you should update your Rails to version 2.0.5 or 2.1.2 to eliminate Header Injection (and thus response splitting) risks._ -h3. Additional resources +h3. Additional Resources The security landscape shifts and it is important to keep up to date, because missing a new vulnerability can be catastrophic. You can find additional resources about (Rails) security here: |