8000 Disable FreeMarker ?new() built-in in themes. by gaoyikeshuer · Pull Request #48280 · keycloak/keycloak · GitHub
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Disable FreeMarker ?new() built-in in themes. #48280

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Merged
stianst merged 1 commit into from
Apr 21, 2026
Merged

Disable FreeMarker ?new() built-in in themes. #48280

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3 changes: 3 additions & 0 deletions docs/guides/ui-customization/themes.adoc
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Expand Up @@ -377,6 +377,9 @@ Themes can be deployed to {project_name} by copying the theme directory to `them
theme to the `themes` directory, but in production you may want to consider using an `archive`. An `archive` makes it simpler to have a versioned copy of
the theme, especially when you have multiple instances of {project_name} for example with clustering.

WARNING: Themes contain FreeMarker templates that the server renders at runtime, so a malicious template can run code as the {project_name} process. Install themes only from trusted sources, and restrict write access to the `themes` directory and to theme JARs under `providers/` to trusted operators.


.Procedure

. To deploy a theme as an archive, create a JAR archive with the theme resources.
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2 changes: 2 additions & 0 deletions services/src/main/java/org/keycloak/theme/freemarker/DefaultFreeMarkerProvider.java
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Expand Up @@ -13,6 +13,7 @@

import freemar 806B ker.cache.URLTemplateLoader;
import freemarker.core.HTMLOutputFormat;
import freemarker.core.TemplateClassResolver;
import freemarker.template.Configuration;
import freemarker.template.Template;

Expand Down Expand Up @@ -63,6 +64,7 @@ private Template getTemplate(String templateName, Theme theme) throws IOExceptio
cfg.setOutputFormat(HTMLOutputFormat.INSTANCE);
}

cfg.setNewBuiltinClassResolver(TemplateClassResolver.ALLOWS_NOTHING_RESOLVER);
cfg.setTemplateLoader(new ThemeTemplateLoader(theme));
return cfg.getTemplate(templateName, "UTF-8");
}
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