11.1 Securing Against Attacks
11.2 Encoding and Decoding Objects
11.3 Authentication
11.4 Security Plug-ins
11.4.1 Spring Security
11.4.2 Shiro
Grails is no more or less secure than Java Servlets. However, Java servlets (and hence Grails) are extremely secure and largely immune to common buffer overrun and malformed URL exploits due to the nature of the Java Virtual Machine underpinning the code.

Web security problems typically occur due to developer naivety or mistakes, and there is a little Grails can do to avoid common mistakes and make writing secure applications easier to write.

What Grails Automatically Does

Grails has a few built in safety mechanisms by default.

  1. All standard database access via GORM domain objects is automatically SQL escaped to prevent SQL injection attacks
  2. The default scaffolding templates HTML escape all data fields when displayed
  3. Grails link creating tags (link, form, createLink, createLinkTo and others) all use appropriate escaping mechanisms to prevent code injection
  4. Grails provides codecs to allow you to trivially escape data when rendered as HTML, JavaScript and URLs to prevent injection attacks here.

11.1 Securing Against Attacks

SQL injection

Hibernate, which is the technology underlying GORM domain classes, automatically escapes data when committing to database so this is not an issue. However it is still possible to write bad dynamic HQL code that uses unchecked request parameters. For example doing the following is vulnerable to HQL injection attacks:

def vulnerable = {
	def books = Book.find("from Book as b where b.title ='" + params.title + "'")

Do not do this. If you need to pass in parameters use named or positional parameters instead:

def safe = {
	def books = Book.find("from Book as b where b.title =?", [params.title])


This really a public relations issue in terms of avoiding hijacking of your branding and a declared communication policy with your customers. Customers need to know how to identify bonafide emails received.

XSS - cross-site scripting injection

It is important that your application verifies as much as possible that incoming requests were originated from your application and not from another site. Ticketing and page flow systems can help this and Grails' support for Spring Web Flow includes security like this by default.

It is also important to ensure that all data values rendered into views are escaped correctly. For example when rendering to HTML or XHTML you must call encodeAsHTML on every object to ensure that people cannot maliciously inject JavaScript or other HTML into data or tags viewed by others. Grails supplies several Dynamic Encoding Methods for this purpose and if your output escaping format is not supported you can easily write your own codec.

You must also avoid the use of request parameters or data fields for determining the next URL to redirect the user to. If you use a successURL parameter for example to determine where to redirect a user to after a successful login, attackers can imitate your login procedure using your own site, and then redirect the user back to their own site once logged in, potentially allowing JS code to then exploit the logged-in account on the site.

HTML/URL injection

This is where bad data is supplied such that when it is later used to create a link in a page, clicking it will not cause the expected behaviour, and may redirect to another site or alter request parameters.

HTML/URL injection is easily handled with the codecs supplied by Grails, and the tag libraries supplied by Grails all use encodeAsURL where appropriate. If you create your own tags that generate URLs you will need to be mindful of doing this too.

Denial of service

Load balancers and other appliances are more likely to be useful here, but there are also issues relating to excessive queries for example where a link is created by an attacker to set the maximum value of a result set so that a query could exceed the memory limits of the server or slow the system down. The solution here is to always sanitize request parameters before passing them to dynamic finders or other GORM query methods:

def safeMax = Math.max(params.max?.toInteger(), 100) // limit to 100 results
return Book.list(max:safeMax)

Guessable IDs

Many applications use the last part of the URL as an "id" of some object to retrieve from GORM or elsewhere. Especially in the case of GORM these are easily guessable as they are typically sequential integers.

Therefore you must assert that the requesting user is allowed to view the object with the requested id before returning the response to the user.

Not doing this is "security through obscurity" which is inevitably breached, just like having a default password of "letmein" and so on.

You must assume that every unprotected URL is publicly accessible one way or another.

11.2 Encoding and Decoding Objects

Grails supports the concept of dynamic encode/decode methods. A set of standard codecs are bundled with Grails. Grails also supports a simple mechanism for developers to contribute their own codecs that will be recognized at runtime.

Codec Classes

A Grails codec class is a class that may contain an encode closure, a decode closure or both. When a Grails application starts up the Grails framework will dynamically load codecs from the grails-app/utils/ directory.

The framework will look under grails-app/utils/ for class names that end with the convention Codec. For example one of the standard codecs that ship with Grails is HTMLCodec.

If a codec contains an encode property assigned a block of code Grails will create a dynamic encode method and add that method to the Object class with a name representing the codec that defined the encode closure. For example, the HTMLCodec class defines an encode block so Grails will attach that closure to the Object class with the name encodeAsHTML.

The HTMLCodec and URLCodec classes also define a decode block so Grails will attach those with the names decodeHTML and decodeURL. Dynamic codec methods may be invoked from anywhere in a Grails application. For example, consider a case where a report contains a property called 'description' and that description may contain special characters that need to be escaped to be presented in an HTML document. One way to deal with that in a GSP is to encode the description property using the dynamic encode method as shown below:


Decoding is performed using value.decodeHTML() syntax.

Standard Codecs


This codec perfoms HTML escaping and unescaping, so that values you provide can be rendered safely in an HTML page without creating any HTML tags or damaging the page layout. For example, given a value "Don't you know that 2 > 1?" you wouldn't be able to show this safely within an HTML page because the > will look like it closes a tag, which is especially bad if you render this data within an attribute, such as the value attribute of an input field.

Example of usage:

<input name="comment.message" value="${comment.message.encodeAsHTML()}"/>

Note that the HTML encoding does not re-encode apostrophe/single quote so you must use double quotes on attribute values to avoid text with apostrophes messing up your page.


URL encoding is required when creating URLs in links or form actions, or any time data may be used to create a URL. It prevents illegal characters getting into the URL to change its meaning, for example a "Apple & Blackberry" is not going to work well as a parameter in a GET request as the ampersand will break the parsing of parameters.

Example of usage:

<a href="/mycontroller/find?searchKey=${lastSearch.encodeAsURL()}">Repeat last search</a>


Performs Base64 encode/decode functions. Example of usage:

Your registration code is: ${user.registrationCode.encodeAsBase64()}


Will escape Strings so they can be used as valid JavaSctipt strings. Example of usage:

Element.update('${elementId}', '${render(template: "/common/message").encodeAsJavaScript()}')


Will encode byte arrays or lists of integers to lowercase hexadecimal strings, and can decode hexadecimal strings into byte arrays. Example of usage:

Selected colour: #${[255,127,255].encodeAsHex()}


Will use the MD5 algorithm to digest byte arrays or lists of integers, or the bytes of a string (in default system encoding), as a lowercase hexadecimal string. Example of usage:

Your API Key: ${user.uniqueID.encodeAsMD5()}


Will use the MD5 algorithm to digest byte arrays or lists of integers, or the bytes of a string (in default system encoding), as a byte array. Example of usage:

byte[] passwordHash = params.password.encodeAsMD5Bytes()


Will use the SHA1 algorithm to digest byte arrays or lists of integers, or the bytes of a string (in default system encoding), as a lowercase hexadecimal string. Example of usage:

Your API Key: ${user.uniqueID.encodeAsSHA1()}


Will use the SHA1 algorithm to digest byte arrays or lists of integers, or the bytes of a string (in default system encoding), as a byte array. Example of usage:

byte[] passwordHash = params.password.encodeAsSHA1Bytes()


Will use the SHA256 algorithm to digest byte arrays or lists of integers, or the bytes of a string (in default system encoding), as a lowercase hexadecimal string. Example of usage:

Your API Key: ${user.uniqueID.encodeAsSHA256()}


Will use the SHA256 algorithm to digest byte arrays or lists of integers, or the bytes of a string (in default system encoding), as a byte array. Example of usage:

byte[] passwordHash = params.password.encodeAsSHA256Bytes()

Custom Codecs

Applications may define their own codecs and Grails will load them along with the standard codecs. A custom codec class must be defined in the grails-app/utils/ directory and the class name must end with Codec. The codec may contain a static encode block, a static decode block or both. The block should expect a single argument which will be the object that the dynamic method was invoked on. For Example:

class PigLatinCodec {
  static encode = { str ->
    // convert the string to piglatin and return the result

With the above codec in place an application could do something like this:


11.3 Authentication

Although there is no current default mechanism for authentication as it is possible to implement authentication in literally thousands of different ways. It is however, trivial to implement a simple authentication mechanism using either interceptors or filters.

Filters allow you to apply authentication across all controllers or across a URI space. For example you can create a new set of filters in a class called grails-app/conf/SecurityFilters.groovy:

class SecurityFilters {
   def filters = {
       loginCheck(controller:'*', action:'*') {
           before = {
              if(!session.user && actionName != "login") {
                  return false					

} } }

Here the loginCheck filter will intercept execution before an action executed and if their is no user in the session and the action being executed is not the login action then redirect to the login action.

The login action itself is trivial too:

def login = {
	if(request.get) render(view:"login")
	else {
		def u = User.findByLogin(params.login)
		if(u) {
			if(u.password == params.password) {
				session.user = u
			else {
				render(view:"login", model:[message:"Password incorrect"])							
		else {
			render(view:"login", model:[message:"User not found"])			

11.4 Security Plug-ins

If you need more advanced functionality beyond simple authentication such as authorization, roles etc. then you may want to consider using one of the available security plug-ins.

11.4.1 Spring Security

The Spring Security plugins are built on the Spring Security project which provides a flexible, extensible framework for building all sorts of authentication and authorization schemes. The plugins are modular so you can install just the functionality that you need for your application. There is a Core plugin which supports form-based authentication, encrypted/salted passwords, HTTP Basic authentication, etc. and secondary dependent plugins provide alternate functionality such as OpenID authentication, ACL support, etc.

See the plugin page for basic information and the user guide for detailed information.

11.4.2 Shiro

Shiro is a Java POJO oriented security framework that provides a default domain model that models realms, users, roles and permissions. With Shiro you have to extends a controller base called called JsecAuthBase in each controller you want secured and then provide an accessControl block to setup the roles. An example below:

class ExampleController extends JsecAuthBase {
    static accessControl = {
        // All actions require the 'Observer' role.
        role(name: 'Observer')

// The 'edit' action requires the 'Administrator' role. role(name: 'Administrator', action: 'edit')

// Alternatively, several actions can be specified. role(name: 'Administrator', only: [ 'create', 'edit', 'save', 'update' ]) }

… }

For more information on the Shiro plugin refer to the documentation.