Sudo like tool for Alfresco – security aspects

In my first post in this blog I proposed a way to execute some javascript code with the admin privileges within the Alfresco (web)scripts.
As Peter Monks pointed out in his comment, there’re some risks concerning security you’d better be aware of if you intend to use this extension in your projects.
As Peter suggested, if users can author their own scripts then they can potentially submit code that runs with administrator privileges, which is an obvious security flow.
Also, attention must be paid in case the eval statement is used within the sudo argument function: avoid this kind of practice if the eval argument itself depends on some webscript input parameter since this could potentially lead to code injection. So how to cope with these problems?
My solution is to create a “sudoers” group (as in the Unix OSs) so that only users that belong to this group can execute the sudo function. Here is how I would change the Sudo bean:

public class Sudo extends BaseScopableProcessorExtension {
    private AuthorityService authorityService;

    public void sudo(final Function func) throws Exception  {
        final Context cx = Context.getCurrentContext();
        final Scriptable scope = getScope();
        String user = AuthenticationUtil.getRunAsUser();

        Set<String> groups = authorityService.getContainingAuthorities(AuthorityType.GROUP, user, false);
        if (!groups.contains("GROUP_SUDOERS"))
            throw new Exception("User '" + user + "' cannot use sudo");

        RunAsWork<Object> raw = new RunAsWork<Object>() {
            public Object doWork() throws Exception {
                func.call(cx, scope, scope, new Object[] {});
                return null;
            }
        };

        AuthenticationUtil.runAs(raw, AuthenticationUtil.getAdminUserName());
    }
}

We used the authorityService service to get the set of groups the current user belongs to and then we checked that the SUDOERS group is one of those. If you use this version of the Sudo bean, remember to update the Spring bean definition (file sudo-script-services-context.xml):

<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE beans PUBLIC '-//SPRING//DTD BEAN//EN' 'http://www.springframework.org/dtd/spring-beans.dtd'>
<beans>
    <bean id="Sudo" parent="baseJavaScriptExtension" class="eu.fabiostrozzi.sudo.ws.js.Sudo">
        <property name="extensionName">
            <value>sudoUtils</value>
        </property>
       <property name="authorityService">
             <ref bean="AuthorityService" />
       </property>
    </bean>
</beans>

This is by no means a fully fledged solution but surely reduces risks if, for instance, users that can author scripts are not added to the SUDOERS group.

  1. I really like this approach.

    Great work!

  2. Sudo for Scripts « Open Source ECM/WCM - pingback on April 29, 2011 at 22:42
  3. Sudo for Scripts in Alfresco « Open Source ECM/WCM - pingback on April 29, 2011 at 22:44
  4. This is much better than the previous solution, but doesn’t this allow anyone in the sudoers group to escalate themselves to full administrator, by submitting a sudo script that adds themself to the administrators group?

    • Yes, of course.
      Consider that when I devised the script, the environment where it was deployed allowed no one other than the administrator to deploy any script.
      So, I think it was quite safe for that scenario but it might not be in your.

      Fabio

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