Difference between revisions of "Hardening new Roles system"

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New roles add great freedom when assigning rights to students. The problem might arise when students are assigned permission that allows adding of content that is not cleaned before display - such as editting Resources, adding activities, etc. They could then use any type of XSS attack to gain full administrative access without any restrictions.
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Hardening a role, refers to limiting the ability of a role to assign or to aquire permissions.
  
==Proposed solution==
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New roles add great freedom when assigning capabilities to students. The problem might arise when students are assigned permission that allows adding of content that is not cleaned before display - such as editting Resources, adding activities, etc. They could then use any type of XSS attack to gain full administrative access quite easily.
Assign trust level to each user and capability. Add trust level checks to has_capability() and require_capability().
 
  
==Implementation==
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The solution has two parts: educate admins and teachers about the risks associated with each capability and optionally allow central management of risks.
* define basic trust levels (as integer constants)
 
** minimal - not logged-in, guests
 
** standard - students and non-editing teachers (must not be able to add HTML with javascript, can not upload files to coursefile area)
 
** high - teachers adding active content and handling sensitive information (backups, editing of activities and resources, uploading of course files, creating courses, etc.)
 
** absolute - usually administrators and trust level managers only
 
* add new column ''trustlevel'' to ''user'' table
 
* add new column ''requiredtrustlevel'' to table ''capabilities''
 
* fix role management GUI
 
** indicate required trust level next to each capability (different color and label or icon)
 
** allow filtering of capabilities based on trust level required
 
* add ''moodle/site:managetrustlevel'' with required absolute trust level
 
* add trust level management GUI
 
** predefined trust level for new users
 
** changing of trust level (also from user/edit page)
 
** request trust level change form (something like new course request)
 
* add trust level checks to has_capability() and require_capability() (veto when user does not have required trust level)
 
* assign levels based on legacy capabilities during upgrade
 
* do security audit of each capability in modules and core; set proper required levels (this is going to be the hardest part)
 
  
==Benefits==
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==Risk bitmask in capabilities==
# Easy to implement, administer and explain to teachers compared to implementation based on capabilities.
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Add risk bitmask field to each capability. Each bit indicates presence of different risk associated with given capability.
# Trust level manager has full control over potentially dangerous capabilities - it is necessary for large sites (or connected sites in the future).
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# Trust level mechanism can be turned off by assigning high level to all users except admins - needed for small insecure ''workshop'' sites.
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===Basic risks===
# Security audits could concentrate on standard and minimal capabilities.
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* '''RISK_SPAM''' - user can add visible content to site, send messages to other users; originally protected by !isguest()
# Module authors will be forced to think about security when defining capabilities.
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* '''RISK_PERSONAL''' - access to private personal information - ex: backups with user details, non public information in profile (hidden email), etc.; originally protected by isteacher()
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* '''RISK_XSS''' - user can submit content that is not cleaned (both HTML with active content and unprotected files); originally protected by isteacher()
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* '''RISK_CONFIG''' - user can change global configuration, actions are missing sanity checks
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* '''RISK_MANAGETRUST''' - manage trust bitmasks of other users
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* '''RISK_DATALOSS''' - can destroy large amounts of information that cannot easily be recovered.
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In default configuration Guest role should have only capabilities without risks, Student roles also SPAM, Teacher roles PERSONAL and XSS too. Admins have all capabilitites by default.
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===Implementation===
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* add new LONGINT column ''riskbitmask'' to table ''capabilities'' (DONE)
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* define risks and assign them to capabilities in mod/xxx/db/access.php and lib/db/access.php (DONE)
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* link wiki pages with explanation to each risk from capabilities page
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* allow risk based filtering of capabilities admin/roles/manage.php (optional)
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The user interface will be minimal, icons and maybe colors indicating each risk together with description links which we need anyway.
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Developers are deciding about the risks, the risk assignment is hardcoded in access.php description file, no GUI needed to change risks.
 +
 
 +
===Benefits===
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# proper documentation of risks associated with capabilities, easy to explain
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# solid foundation for regular code audits (mainly XSS prevention and personal information disclosure)
 +
 
 +
==User trust bitmask==
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Indicate what kind of trust each user has. Match the risk bitmask of capability and user trust bitmask in both has_capability() and require_capability().
 +
 
 +
===Implementation===
 +
* add new LONGINT column ''trustbitmask'' to ''user'' table
 +
* add capability ''moodle/site:managetrustbitmasks'' with RISK_MANAGETRUST risk
 +
* add trust checks to has_capability() and require_capability()
 +
* add GUI
 +
** switch in global configuration to enable trust bitmask checking
 +
** preseting of trust bitmask for new users
 +
** changing of trust bitmasks
 +
** add trust bitmask setting to user/edit.php
 +
** request trust level change form - something like new course request (optional)
 +
* fix upgrade to assign trust bitmaps based on original teacher or administrator rights
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* patch user import script and synchronizations (optional)
 +
 
 +
===Benefits===
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# This part is optional and can be implemented later.
 +
# Trust manager or admin has full control over potentially dangerous capabilities - it is necessary for large sites (or connected sites in the future).  
 +
# Trust bitmask mechanism can be turned off by single configuration switch (both GUI and checks) - needed for small insecure workshop sites.
 +
# General protection against future bugs in role and capability framework or user errors when configuring roles.
 +
 
 +
 
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''Note: trusttext moved to its own page at [[Trusttext cleaning bypass]]''
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[[Category:Roles]]

Latest revision as of 08:24, 10 June 2011

Hardening a role, refers to limiting the ability of a role to assign or to aquire permissions.

New roles add great freedom when assigning capabilities to students. The problem might arise when students are assigned permission that allows adding of content that is not cleaned before display - such as editting Resources, adding activities, etc. They could then use any type of XSS attack to gain full administrative access quite easily.

The solution has two parts: educate admins and teachers about the risks associated with each capability and optionally allow central management of risks.

Risk bitmask in capabilities

Add risk bitmask field to each capability. Each bit indicates presence of different risk associated with given capability.

Basic risks

  • RISK_SPAM - user can add visible content to site, send messages to other users; originally protected by !isguest()
  • RISK_PERSONAL - access to private personal information - ex: backups with user details, non public information in profile (hidden email), etc.; originally protected by isteacher()
  • RISK_XSS - user can submit content that is not cleaned (both HTML with active content and unprotected files); originally protected by isteacher()
  • RISK_CONFIG - user can change global configuration, actions are missing sanity checks
  • RISK_MANAGETRUST - manage trust bitmasks of other users
  • RISK_DATALOSS - can destroy large amounts of information that cannot easily be recovered.

In default configuration Guest role should have only capabilities without risks, Student roles also SPAM, Teacher roles PERSONAL and XSS too. Admins have all capabilitites by default.

Implementation

  • add new LONGINT column riskbitmask to table capabilities (DONE)
  • define risks and assign them to capabilities in mod/xxx/db/access.php and lib/db/access.php (DONE)
  • link wiki pages with explanation to each risk from capabilities page
  • allow risk based filtering of capabilities admin/roles/manage.php (optional)

The user interface will be minimal, icons and maybe colors indicating each risk together with description links which we need anyway. Developers are deciding about the risks, the risk assignment is hardcoded in access.php description file, no GUI needed to change risks.

Benefits

  1. proper documentation of risks associated with capabilities, easy to explain
  2. solid foundation for regular code audits (mainly XSS prevention and personal information disclosure)

User trust bitmask

Indicate what kind of trust each user has. Match the risk bitmask of capability and user trust bitmask in both has_capability() and require_capability().

Implementation

  • add new LONGINT column trustbitmask to user table
  • add capability moodle/site:managetrustbitmasks with RISK_MANAGETRUST risk
  • add trust checks to has_capability() and require_capability()
  • add GUI
    • switch in global configuration to enable trust bitmask checking
    • preseting of trust bitmask for new users
    • changing of trust bitmasks
    • add trust bitmask setting to user/edit.php
    • request trust level change form - something like new course request (optional)
  • fix upgrade to assign trust bitmaps based on original teacher or administrator rights
  • patch user import script and synchronizations (optional)

Benefits

  1. This part is optional and can be implemented later.
  2. Trust manager or admin has full control over potentially dangerous capabilities - it is necessary for large sites (or connected sites in the future).
  3. Trust bitmask mechanism can be turned off by single configuration switch (both GUI and checks) - needed for small insecure workshop sites.
  4. General protection against future bugs in role and capability framework or user errors when configuring roles.


Note: trusttext moved to its own page at Trusttext cleaning bypass