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URL Level Access Control Cheat Sheet

Revision as of 16:26, 30 January 2013 by Jason Johnson (talk | contribs)

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This article is focused on providing clear, simple, actionable guidance for providing Access Control security in your applications.

What is URL Level Access Control?

Attacks on URL Level Access Control

URL Level Access Control Issues

Access Control Anti-Patterns

Order Specific Operations

Imagine the following parameters

Can an attacker control the sequence?

Can an attacker abuse this with concurency?

Never Depend on Untrusted Data

  • Never trust user data for access control decisions
  • Never make access control decisions in JavaScript
  • Never depend on the order of values sent from the client
  • Never make authorization decisions based solely on
    • hidden fields
    • cookie values
    • form parameters
    • URL parameters
    • anything else from the request

Attacking Access Controls

  • Elevation of privileges
  • Disclosure of confidential data - Compromising admin-level accounts often result in access to a user's confidential data
  • Data tampering - Privilege levels do not distinguish users who can only view data and users permitted to modify data

Testing for Broken Access Control

  • Attempt to access administrative components or functions as an anonymous or regular user
    • Scour HTML source for “interesting” hidden form fields
    • Test web accessible directory structure for names like admin, administrator, manager, etc (i.e. attempt to directly browse to “restricted” areas)
  • Determine how administrators are authenticated. Ensure that adequate authentication is used and enforced
  • For each user role, ensure that only the appropriate pages or components are accessible for that role.
  • Login as a low-level user, browse history for a higher level user’s cache, load the page to see if the original authorization is passed to a previous session.
  • If able to compromise administrator-level account, test for all other common web application vulnerabilities (poor input validation, privileged database access, etc)

Defenses Against Access Control Attacks

  • Implement role based access control to assign permissions to application users for vertical access control requirements
  • Implement data-contextual access control to assign permissions to application users in the context of specific data items for horizontal access control requirements
  • Avoid assigning permissions on a per-user basis
  • Perform consistent authorization checking routines on all application pages
  • Where applicable, apply DENY privileges last, issue ALLOW privileges on a case-by-case basis
  • Where possible restrict administrator access to machines located on the local area network (i.e. it’s best to avoid remote administrator access from public facing access points)
  • Log all failed access authorization requests to a secure location for review by administrators
  • Perform reviews of failed login attempts on a periodic basis
  • Utilize the strengths and functionality provided by the SSO solution you chose

Best Practices

Best Practice: Code to the Activity

  if (AC.hasAccess(ARTICLE_EDIT)) {
      //execute activity
  • Code it once, never needs to change again
  • Implies policy is persisted/centralized in some way
  • Avoid assigning permissions on a per-user basis
  • Requires more design/work up front to get right

Best Practice: Centralized ACL Controller

  • Define a centralized access controller
  • Access control decisions go through these simple API’s
  • Centralized logic to drive policy behavior and persistence
  • May contain data-driven access control policy information
  • Policy language needs to support ability to express both access rights and prohibitions

Best Practice: Using a Centralized Access Controller

  • In Presentation Layer
      if (isAuthorized(VIEW_LOG_PANEL))
         Here are the logs
  • In Controller
      try (assertAuthorized(DELETE_USER))

Best Practice: Verifying policy server-side

  • Keep user identity verification in session
  • Load entitlements server side from trusted sources
  • Force authorization checks on ALL requests
    • JS file, image, AJAX and FLASH requests as well!
    • Force this check using a filter if possible

SQL Integrated Access Control

Example Feature

This SQL would be vulnerable to tampering

 select * from messages where messageid = 2356342

Ensure the owner is referenced in the query!

 select * from messages where messageid = 2356342 AND messages.message_owner = 

Access Control Positive Patterns

Data Contextual Access Control

Data Contextual / Horizontal Access Control API examples

   ACLService.isAuthorized(EDIT_ORG, 142)
   ACLService.assertAuthorized(VIEW_ORG, 900)

Long Form

   isAuthorized(user, EDIT_ORG, Organization.class, 14)
  • Essentially checking if the user has the right role in the context of a specific object
  • Centralize access control logic
  • Protecting data at the lowest level!

Related Articles

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