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Working with macro signatures

Whenever a user saves a macro expression, the system automatically adds a security signature. The signature contains the user name 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.

Unsuccessful security checks prevent the system from resolving macros. If you encounter such problems, you can view the event log or the macro debug log, which provide information about performed security checks and their results.

Tip: You can confirm whether your macros have valid signatures by searching for expressions in System -> Macros -> Report.

See: Searching for macros



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Disabling the security signature for specific macros

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

{% CurrentPageInfo.DocumentName @%}

These macros do not store the user name of the author or the security hash, so the internal length of the expression does not exceed the visible number of characters. This allows you to safely use macros in fields with a limited character count.

Unsigned macros are always evaluated with the permissions of a public user.

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.

Warning

Changing the salt causes all current hash values to become invalid, including the signatures of macros. Having invalid macros throughout the system may lead to problems on your website, and also prevents the Kentico administration from working correctly. You need to re-sign macros immediately after changing the hash salt value.

In addition to macro signatures, the system uses the CMSHashStringSalt value for other hash functions. Changing the hash salt on a website that already has defined content may break dialog links and images on your website. If you encounter such problems, you need to re-save the given content (the system then creates the hashes using the new salt).

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;

    If you enable Sign all macros, the macro re-signing process skips the signature integrity check and creates new signatures for all macros. You do not need to enter the old salt value in this case. The new signatures contain the name of the user who started the re-signing procedure.

    Security warning: With the Sign all macros option enabled, the resigning process also includes macros that are unsigned or have invalid signatures. If your system's data contains invalid macros added by users with insufficient authorization, such macros receive valid signatures and represent potential security threats.

  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.