Working with macro signatures

Whenever a user saves a macro expression, the system automatically adds a security signature. Signatures prevent macros from accessing or displaying data for which the author is not authorized.

Every macro signature contains an identifier of the macro’s author and a hash of the given expression. To increase the level of security, the hash function used when creating macro signatures appends a salt to the input (a sequence of additional characters). The salt value depends on the configuration of the application’s environment, so the signatures are in most cases not valid when deploying macros to other instances of Kentico.

You can recognize signed macro expressions by the # character, which the system automatically inserts before the closing %} parentheses when saving the text containing the macro.

{% CurrentUser.Children["cms_category"][0].CategoryName #%}

If the execution of the macro requires any permissions, the system resolves the macro only if the user specified by the signature has the appropriate permissions.

Permissions are only checked when resolving macro expressions that:

• access objects that are members of another object, for example: {% CurrentDocument.DocumentPageTemplate %}
• access collections of objects, for example: {% CurrentUser.Children[“cms_category”][0].CategoryName %}

The system carries out a security check for each access to any collection, not just for the final macro result.

Disabling the security signature for specific macros

You can stop the system from adding macro signatures by manually adding the @ character before the closing %} sequence of a macro:

{% CurrentPageInfo.DocumentName @%}

Unsigned macros are always evaluated with the permissions of a public user. As a result, expressions that require any permissions will not resolve correctly when unsigned.

The advantage of unsigned macros is that they do not store an identifier of the author or a security hash. This allows you to:

• Add macros into fields that have a limited character count (unsigned macro expressions have the same internal length as the visible number of characters)
• Create macros that are easier to deploy to other Kentico instances (they do not rely on a specific user or identity, and the environment’s hash salt value)

Configuring the hash salt for macro signatures

The system appends a salt to the input of the hash function that creates macro signatures.

By default, new instances of Kentico use a randomly generated GUID as the hash salt. The installer sets the custom salt value through the CMSHashStringSalt key in the appSettings section of the web.config file. Instances without this web.config key use the application’s main database connection string as the salt (the exact CMSConnectionString value in the web.config file). We strongly recommend using a custom salt (CMSHashStringSalt).

A custom salt provides the following benefits:

• Stability (you do not need to re-sign macros if your connection string changes)
• You can use the same salt for other instances of Kentico, which makes deployment easier and allows content staging of macros

The best option is to set the hash salt value before you start creating content for your website.

To change the salt value for your application, edit the value of the CMSHashStringSalt key in your web.config file. You can use any string as the value, but the salt should be random and at least 16 characters long. For example:

<add key="CMSHashStringSalt" value="e68b9ad6-a461-4707-8e3e-ece73f03dd02" />

Re-signing macros

If the hash salt value used by your application changes, the security signatures of existing macro expressions become invalid. For example, you may encounter problems with unresolved macros:

• After setting a new custom salt via the CMSHashStringSalt web.config key.
• When using Content staging to transfer data containing macros to an instance of Kentico with a different hash salt.
• If your application does not have a custom hash salt, and the connection string has changed (for example when moving to a different server or after setting a new database password).

To re-sign individual macros, find the expression in the user interface and save the value (you can use the macro report tool to find the location). The system creates a new signature for the macro based on the application’s current environment.

You can also repair invalid macro signatures by re-signing all macros in the system:

1. Go to System -> Macros -> Signatures.

2. Fill in the Old salt field.

   If you leave the Sign all macros option disabled, the system checks the original signatures before re-signing macros. Only macros that have a valid signature under the old salt are re-signed and the user names of the macro authors remain unchanged. You need to enter the old salt that was used to generate the security hash of the existing macro expressions in the system.

   • If your application uses a custom hash salt, enter the original value of the CMSHashStringSalt web.config key.
   • If the original hash salt was a connection string, enter the value in format:
     Persist Security Info=False;database=DBName;server=ServerName;user id=DBUser;password=pwd;Current Language=English;Connection Timeout=240;

3. Type in the New salt that will be used to re-sign the macros.

   • By default, the field automatically loads the current application’s hash salt value. To enter a different value, disable the Use current salt option.

     Important

     In order for the system to correctly validate macro signatures, the new hash salt value must match the application’s current salt (the CMSHashStringSalt key value or connection string). Only change the New salt value if you are planning to change your application salt.

4. Click Update macro signatures.

 The system replaces the security signature in all occurrences of macros based on the new salt.