Difference between revisions of "Configuration"

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We want to write as clean code as possible and thus we want PHP to throw all warnings etc at us.  
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We want to write as clean code as possible and thus we want PHP to throw all warnings, etc. at us.  
  
 
Recommended: E_ALL  
 
Recommended: E_ALL  

Revision as of 10:42, 4 March 2009

Development Guide Table of Contents

Contents


Objective

To produce applications which are secure out of the box.

Platforms Affected

All.

Relevant COBIT Topics

DS6 – Manage Changes – All sections should be reviewed

Best Practices

Turn off all unnecessary features by default

  • Ensure that all switches and configuration for every feature is configured initially to be the safest possible choice.
  • Inspect the design to see if the less safe choices could be designed in another way. For example, password reset systems are intrinsically unsound from a security point of view. If you do not ship this component, your application’s users will be safer.
  • Do not rely on optionally installed features in the base code.
  • Do not configure anything in preparation for an optionally deployable feature.

Default passwords

Applications often ship with well-known passwords. In a particularly excellent effort, NGS Software determined that Oracle’s “Unbreakable” database server contained 168 default passwords out of the box. Obviously, changing this many credentials every time an application server is deployed is out of the question, nor should it be necessary.

How to identify if you are vulnerable

  • Inspect the application’s manifest and ensure that no passwords are included in any form, whether within the source files, compiled into the code, or as part of the configuration.
  • Inspect the application for usernames and passwords. Ensure that diagrams also do not have any.

How to protect yourself

  • Do not ship the product with any configured accounts.
  • Do not hard code any backdoor accounts or special access mechanisms.

Secure connection strings

Connection strings to the database are rarely encrypted. However, they allow a remote attacker who has shell access to perform direct operations against the database or back end systems, thus providing a leap point for total compromise.

How to identify if you are vulnerable

  • Check your framework’s configuration file, registry settings, and any application based configuration file (usually config.php, etc) for clear text connection strings to the database.

How to protect yourself

  • Sometimes, no password is just as good as a clear text password.
  • On the Win32 platform, use “TrustedConnection=yes”, and create the DSN with a stored credential. The credential is stored as a LSA Secret, which is not perfect, but is better than clear text passwords.
  • Develop a method to obfuscate the password in some form, such as “encrypting” the name using the hostname or similar within code in a non-obvious way.
  • Ask the database developer to provide a library which allows remote connections using a password hash instead of a clear text credential.

Secure network transmission

By default, no unencrypted data should transit the network.

How to identify if you are vulnerable

  • Use a packet capture tool, such as Ethereal and mirror a switch port near the database or application servers.
  • Sniff the traffic for a while and determine your exposure to an attacker performing this exact same task.

How to protect yourself

  • Use SSL, SSH and other forms of encryption (such as encrypted database connections) to prevent data from being intercepted or interfered with over the wire.

Encrypted data

Some information security policies and standards require the database on-disk data to be encrypted. However, this is essentially useless if the database connection allows clear text access to the data. What is more important is the obfuscation and one-way encryption of sensitive data.

How to identify if you are vulnerable

Highly protected applications:

  • Is there a requirement to encrypt certain data?
  • If so, is it “encrypted” in such a fashion that allows a database administrator to read it without knowing the key?

If so, the “encryption” is useless and another approach is required.

How to protect yourself

Highly protected applications and any application that has a requirement to encrypt data:

  • Passwords should only be stored in a non-reversible format, such as SHA-256 or similar
  • Sensitive data like credit cards should be carefully considered – do they have to be stored at all? The PCI guidelines are very strict on the storage of credit card data. We strongly recommend against it.
  • Encrypted data should not have the key on the database server.

The last requirement requires the attacker to take control of two machines to bulk decrypt data. The encryption key should be able to be changed on a regular basis, and the algorithm should be sufficient to protect the data in a temporal timeframe. For example, there is no point in using 40 bit DES today; data should be encrypted using AES-128 or better.

PHP Configuration

Global variables

Variables declared outside of functions are considered global by PHP. The opposite is that a variable declared inside a function, is considered to be in local function scope. PHP handles global variables quite differently than languages like C. In C, a global variable is always available in local scope as well as global, as long as it is not overridden by a local definition. In PHP things are different; to access a global variable from local scope you have to declare it global in that scope. The following example shows this:


$sTitle = 'Page title'; // Global scope


function printTitle()

{

global $sTitle; // Declare the variable as global

	echo $sTitle; // Now we can access it just like it was a local variable

}

All variables in PHP are represented by a dollar sign followed by the name of the variable. The names are case-sensitive and must start with a letter or underscore, followed by any number of letters, numbers, or underscores.

register_globals

The register_globals directive makes input from GET, POST and COOKIE, as well as session variables and uploaded files, directly accessible as global variables in PHP. This single directive, if set in php.ini, is the root of many vulnerabilities in web applications.

Let's start by having a look at an example:


if ($bIsAlwaysFalse) 

{ 

	// This is never executed:

	$sFilename = 'somefile.php';

}''

//       ...

if ( $sFilename != '' )   

{

	// Open $sFilename and send it's contents to the browser  

	//		... 

}

 

If we were to call this page like: page.php?sFilename=/etc/passwd with register_globals set, it would be the same as to write the following:


$sFilename = '/etc/passwd'; // This is done internally by PHP       

if ( $bIsAlwaysFalse )

{       // This is never executed:         

	$sFilename = 'somefile.php';

}

// ...

if ( $sFilename != '' )

{

	// Open $sFilename and send it's contents to the browser

	// ...

}

PHP takes care of the $sFilename = '/etc/passwd'; part for us. What this means is that a malicious user could inject his/her own value for $sFilename and view any file readable under the current security context.

We should always think of that “what if” when writing code. So turning off register_globals might be a solution but what if our code ends up on a server with register_globals on. We must bear in mind that all variables in global scope could have been tampered with. The correct way to write the above code would be to make sure that we always assign a value to $sFilename:


// We initialize $sFilename to an empty string

$sFilename = '';

if ( $bIsAlwaysFalse ) { 	    

// This is never executed:     

$sFilename = 'somefile.php';

}

...

if ( $sFilename != '' ) {     

// Open $sFilename and send it's contents to the browser

...

}

Another solution would be to have as little code as possible in global scope. Object oriented programming (OOP) is a real beauty when done right and I would highly recommend you to take that approach. We could write almost all our code in classes that is generally safer and promotes reuse. Like we never should assume that register_globals is off, we should never assume it is on. The correct way to get input from GET, POST, COOKIE etc. is to use the superglobals that were added in PHP version 4.1.0. These are the $_GET, $_POST, $_ENV, $_SERVER, $_COOKIE, $_REQUEST $_FILES, and $_SESSION arrays. The term superglobals is used since they are always available without regard to scope.

register_globals

If set PHP will create global variables from all user input coming from get, post and cookie. If you have the opportunity to turn off this directive you should definitely do so. Unfortunately there is so much code out there that uses it so you are lucky if you can get away with it.

Recommended: off

safe_mode

The PHP safe mode includes a set of restrictions for PHP scripts and can really increase the security in a shared server environment. To name a few of these restrictions: A script can only access/modify files and folders which has the same owner as the script itself. Some functions/operators are completely disabled or restricted, like the backtick operator.

disable_functions

This directive can be used to disable functions of our choosing.

open_basedir

Restricts PHP so that all file operations are limited to the directory set here and its subdirectories.

allow_url_fopen

With this option set PHP can operate on remote files with functions like include and fopen.

Recommended: off

error_reporting

We want to write as clean code as possible and thus we want PHP to throw all warnings, etc. at us.

Recommended: E_ALL

log_errors

Logs all errors to a location specified in php.ini.

Recommended: on

display_errors

With this directive set, all errors that occur during the execution of scripts, with respect to error_reporting, will be sent to the browser. This is desired in a development environment but not on a production server, since it could expose sensitive information about our code, database or web server.

Recommended: off (production), on (development)

magic_quotes_gpc

Escapes all input coming in from post, get and cookie. This is something we should handle on our own.

This also applies to magic_quotes_runtime.

Recommended: off

post_max_size, upload_max_filesize and memory_limit

These directives should be set at a reasonable level to reduce the risk of resource starvation attacks.

Database security

Data obtained from the user needs to be stored securely. In nearly every application, insufficient care is taken to ensure that data cannot be obtained from the database itself.

How to identify if you are vulnerable

  • Does the application connect to the database using low privilege users?
  • Are there different database connection users for application administration and normal user activities? If not, why not?
  • Does the application make use of safer constructs, such as stored procedures which do not require direct table access?
  • Highly protected applications:
    • Is the database is on another host? Is that host locked down?
    • All patches deployed and latest database software in use?
    • Does the application connect to the database using an encrypted link? If not, is the application server and database server in a restricted network with minimal other hosts, particularly untrusted hosts like desktop workstations?

How to protect yourself

  • The application should connect to the database using as low privilege user as is possible.
  • The application should connect to the database with different credentials for every trust distinction (eg, user, read-only user, guest, administrators) and permissions applied to those tables and databases to prevent unauthorized access and modification.
  • The application should prefer safer constructs, such as stored procedures which do not require direct table access. Once all access is through stored procedures, access to the tables should be revoked.
  • Highly protected applications:
    • The database should be on another host, which should be locked down with all current patches deployed and latest database software in use.
    • The application should connect to the database using an encrypted link. If not, the application server and database server must reside in a restricted network with minimal other hosts.
    • Do not deploy the database server in the main office network.

Further Reading

ColdFusion Components (CFCs)

This section provides guidance on using ColdFusion components (CFCs) without exposing your web application to unnecessary risk. ColdFusion provides two ways of restricting access to CFCs; role-based security and access control.

Role-based security is implemented by the roles attribute of the <cffunction> tag. The attribute contains a comma-delimited list of security roles that can call this method.

Access control is implemented by the access attribute of the <cffunction> tag. The possible values of the attribute in order of most restricted behavior are: private (strongest), package, public (default), and remote (weakest).


Private: The method is accessible only to methods within the same component. This is similar to the Object Oriented Programming (OOP) private identifier.

Package: The method is accessible only to other methods within the same package. This is similar to the OOP protected static identifier.

Public: The method is accessible to any CFC or CFM on the same server. This is similar to the OOP public static identifier.

Remote: Allows all the privileges of public, in addition to accepting remote requests from HTML forms, Flash, or a web services. This option is required, to publish the function as a web service.


Best Practices

  • Do not use THIS scope inside a component to expose properties. Use a getter or setter function instead. For example, instead of using THIS.myVar create a public function that sets the variable (i.e. setMyVar(value)).
  • Do not omit the role attribute as ColdFusion will not restrict user access to the function.
  • Avoid using Access=”Remote” if you do not intend to call the component directly from a URL.

Configuration

The following section describes some of the server-wide security-related options available to a ColdFusion administrator via the ColdFusion MX 7 Administrator console web application (http://servername:port/CFIDE/administrator/index.cfm). If the console application is unavailable, you can modify these options by editing the XML files in the cf_root/lib/ (Server configuration) or cf_web_root/WEB-INF/cfusion/lib (J2EE configuration) directory; however, editing these files directly is not recommended.


Best Practice

  • CF Admin Password screen
  • Enable a strong Administrator password
    • The ColdFusion Administrator is the default interface for configuring the ColdFusion application server. It is secured by a single password. Ensure that the Administrator security is enabled and the password is strong and stored in a secure place.
    • Ensure the checkbox is filled
    • Enter and confirm a strong password string of 8 characters or more
    • Click Submit Changes


Sandbox Security screen

Enable Sandbox Security


The ColdFusion Sandbox allows you to place access security restrictions on files, directories, methods, and data sources. Sandboxes make the most sense for a hosting provider or corporate intranet where multiple applications share the same server. Enable this option.

Next, a sandbox needs to be configured, because if not all code in all directories will execute without restriction. Code in a directory and its subdirectories inherits the access controls defined for the sandbox. For example, if ABC Company creates multiple applications within their directory all applications will have the same permissions as the parent. A sandbox applied to ABC-apps will apply to app1 and app2. A sample directory structure is shown below:


D:\inetpub\wwwroot\ABC-apps\app1

D:\inetpub\wwwroot\ABC-apps\app2


Note: if a new sandbox is created for app2 then it will not inherit settings from ABC-apps.


Sandbox security configurations are application specific; however, there are general guidelines that should be followed:


Create a default restricted sandbox and copy setting to each subsequent sandbox removing restrictions as needed by the application. Except in the case of files/directories where access is granted rather than restricted.

Restrict access to data sources that should not be accessed by the sandboxed application.

Restrict access to powerful tags, for example CFREGISTRY and CFEXECUTE.

Restrict file and directory access to limit the ability of tags and functions to perform actions to specified paths.

Every application should have a sandbox.

In multi-homed environments disable Java Server Pages (JSP) as ColdFusion is unable to restrict the functionality of the underlying Java server.


RDS Password screen

Enable a strong RDS password


Developers can access ColdFusion resources (files and data sources) over HTTP from Macromedia Dreamweaver MX and HomeSite+ through ColdFusion’s Remote Development Services (RDS). This feature is password protected should only be enabled in secure development environments.


Ensure the checkbox is filled

Enter and confirm a strong password string of 8 characters or more

Click Submit Changes


Use RDS over SSL - During development, you should use SSL v3 to encrypt all RDS communications between Dreamweaver MX and the ColdFusion server. This includes remote access to server data sources and drives, provided that both are accessed through RDS.


Disable RDS in Production


In production environments, you should not use RDS. In earlier versions of ColdFusion, RDS ran as a separate service or process and could be disabled by disabling the service. In ColdFusion MX, RDS is integrated into the main service. To disable it, you must disable the RDSServlet mapping in the web.xml file. The following procedure assumes that ColdFusion is installed in the default location.


1. Back up the C:\CFusionMX7\wwwroot\WEB-INF\web.xml file.

2. Open the web.xml file for editing.

3. Comment out the RDSServlet mapping, as follows:

<!—

<servlet-mapping>

<servlet-name>RDSServlet</servlet-name>

<url-pattern>/CFIDE/main/ide.cfm</url-pattern>

</servlet-mapping>

-->

4. Save the file.

5. Restart ColdFusion.


Settings Screen

Enable a Request Timeout


ColdFusion processes requests simultaneously and queues all requests above the configured maximum number of simultaneous requests. If requests run abnormally long, this can tie up server resources and lead to DoS attacks. This setting will terminate requests when the configured timeout is reached.


Fill the checkbox next to “Timeout Request after (seconds)”

Enter the number of seconds for ColdFusion to allow threads to run


To allow a valid template request to run beyond the configured timeout, place a <cfsetting> atop the base ColdFusion template and configure the RequestTimeout attribute for the necessary amount of time (in seconds).


Use UUID for cftoken


Best practice calls for J2EE session management. In the event that only ColdFusion session management is available, strong security identifiers must be used. Enable this setting to change the default 8-character CFToken security token string to a UUID.


Enable Global Script Protection - This is a new security feature in ColdFusion MX 7 that isn’t available in other web application platforms. It helps protect Form, URL, CGI, and Cookie scope variables from cross-site scripting attacks.


Specify a Site-wide Error Handler


Prevent information leaks through verbose error messages. Specifying a site-wide error handler covers you when cftry/cfcatch are not used. This page should be a generic error message that you return to the user. Also, if the error handler displays user-input, it should be reviewed for potential cross-site scripting issues.


Specify a Missing Template Handler


Provide a custom message page for HTTP 404 errors when the server cannot find the requested ColdFusion template.


Configure a memory throttling


To prevent file upload DoS attacks, Macromedia added new configuration settings to ColdFusion MX 7.0.1 that allow administrators to restrict the total upload size of HTTP POST operations. Configure these settings accordingly.


maximum size for post data


This is the total size that ColdFusion will accept for any single HTTP POST request (including file uploads). ColdFusion will reject any request whose Content-size header exceeds this setting.


Request Throttle Threshold


HTTP POST requests larger than this setting (default is 4MB) are included in the total concurrent request memory size and get queued if they exceed the Request Throttle Memory setting.


Request Throttle Memory


This sets the total amount of memory (MB) ColdFusion reserves for concurrent HTTP POST requests. Any requests exceeding this limit are queued until enough memory is available.


Memory Variables screen

Enable J2EE Session Management and Use J2EE session variables.


Best practice requires J2EE sessions because they are more secure than regular ColdFusion sessions. (See Session Management section)

Select checkbox next to “Enable Session Variables”

Select checkbox next to “Enable J2EE session variables”


Set the maximum session timeout to 20 minutes to limit the window of opportunity for session hijacking.


Set the default session timeout to 20 minutes to limit the window of opportunity for session hijacking. (The default value is 20 minutes.)


The session-timeout parameter in the cf_root/WEB-INF/web.xml file establishes the maximum J2EE session timeout. This setting should always be greater-than or equal-to ColdFusion’s Maximum Session Timeout value.


Set the maximum application timeout to 24 hours.


Set the default application timeout to 8 hours.


Data Sources screen

Do not use an administrative account to connect ColdFusion to a data source. For example, do not use SA account to connect to a MS SQL Server. The account accessing the database should be granted specific privileges to the objects it needs to access. In addition, the account created to connect the database should be an OS-based, not a SQL account. Operating system accounts have many more auditing, password, and other security controls associated with them. For example, account lockouts and password complexity requirements are built into the Windows operating system; however, a database would need custom code to handle these security-related tasks.


Disable the following Allowed SQL options for all data sources:


Create

Drop

Grant

Revoke

Alter


As an administrator, you do not have control over what a developer sends to the database; however, there should be no circumstance where the previous commands need to be sent to a database from a web application.


Debugging Settings screen

Disable Robust Exception for production servers. (Default)


Disable Debugging for production servers. (Default)


Debugging IP Addresses

Ensure only the addresses of trusted clients are in the IP list.


Only allow the localhost IP (127.0.0.1) in the list on production machines


Mail screen

Require a user name and password to authenticate to your mail server.


Set the connection timeout to 60 seconds (The default value is 60 seconds.)

Links

Development Guide Table of Contents