2FA Enforcement on the instance: a user logging in with SSO can bypass 2FA enforcement

Summary

On GitLab 17.8.4-ee, when 2FA is enforced on the instance with grace period 0, when a user logs in with email address / username and password, they are rightly prompted to setup 2FA on the next login. However, if they log in via SSO, they can simply bypass this requirement. A customer who originally reported this, is using OmniAuth with Amazon Cognito. However, I see the same if I simply log in with SAML to my test instance. My SAML configuration looks like this:

gitlab_rails['omniauth_allow_single_sign_on'] = ['saml']
gitlab_rails['omniauth_block_auto_created_users'] = false

gitlab_rails['omniauth_auto_link_saml_user'] = true
gitlab_rails['omniauth_providers'] = [
  {
    name: "saml",
    groups_attribute: "Groups",
    label: "Azure", # optional label for login button, defaults to "Saml"
    args: {
      assertion_consumer_service_url: [REDACTED],
      idp_cert_fingerprint: "myThumbprint",
      idp_sso_target_url: [REDACTED],
      issuer: [REDACTED]",
      name_identifier_format: "urn:oasis:names:tc:SAML:2.0:nameid-format:persistent",
            attribute_statements: {
               email: ['email'],
               name: ['displayname'],
               first_name: ['firstname'],
               last_name: ['lastname']
             }
    }
  }
]

Which means I don't have upstream_two_factor_authn_contexts configured, which would allow me to bypass 2FA.

This is quite an urgent issue for our customer. They are a very big customer, and this is a security concern for them. Ticket: https://gitlab.zendesk.com/agent/tickets/609760

Steps to reproduce

  • Spin up a 17.8.4-ee instance.
  • Enforce 2FA on the instance with grace period 0
  • Create a test user which you can use to log in with email address and password
  • Log in and check that the user is being asked to setup 2FA
  • Configure SAML for the instance, making sure not to set upstream_two_factor_authn_contexts
  • Now add said user to a SAML app
  • Login via SAML in a new incognito window
  • Notice that now the user isn't being prompted to setup 2FA

Example Project

This happens on my test instance: [REDACTED] And also for the customer.

What is the current bug behavior?

Using SSO lets the user bypass the instance level 2FA requirement.

What is the expected correct behavior?

Using SSO should not let the customer get around the 2FA enforcement requirement.

Relevant logs and/or screenshots

Output of checks

Results of GitLab environment info

Expand for output related to GitLab environment info 

root@sr-env-0472d3c0-omnibus:~# sudo gitlab-rake gitlab:env:info

System information
System:		Ubuntu 20.04
Proxy:		no
Current User:	git
Using RVM:	no
Ruby Version:	3.2.5
Gem Version:	3.5.23
Bundler Version:2.5.11
Rake Version:	13.0.6
Redis Version:	7.0.15
Sidekiq Version:7.2.4
Go Version:	unknown

GitLab information
Version:	17.8.4-ee
Revision:	74ddb379313
Directory:	/opt/gitlab/embedded/service/gitlab-rails
DB Adapter:	PostgreSQL
DB Version:	14.15
URL:		https://sr-env-0472d3c0-omnibus.env-0472d3c0.gcp.gitlabsandbox.net
HTTP Clone URL:	https://sr-env-0472d3c0-omnibus.env-0472d3c0.gcp.gitlabsandbox.net/some-group/some-project.git
SSH Clone URL:	git@sr-env-0472d3c0-omnibus.env-0472d3c0.gcp.gitlabsandbox.net:some-group/some-project.git
Elasticsearch:	no
Geo:		no
Using LDAP:	no
Using Omniauth:	yes
Omniauth Providers: saml

GitLab Shell
Version:	14.39.0
Repository storages:
- default: 	unix:/var/opt/gitlab/gitaly/gitaly.socket
GitLab Shell path:		/opt/gitlab/embedded/service/gitlab-shell

Gitaly
- default Address: 	unix:/var/opt/gitlab/gitaly/gitaly.socket
- default Version: 	17.8.4
- default Git Version: 	2.47.0

(For installations from source run and paste the output of:
`sudo -u git -H bundle exec rake gitlab:env:info RAILS_ENV=production`)

Results of GitLab application Check

Expand for output related to the GitLab application check 
root@sr-env-0472d3c0-omnibus:~# sudo gitlab-rake gitlab:check SANITIZE=true
Checking GitLab subtasks ...


Checking GitLab Shell ...


GitLab Shell: ... GitLab Shell version >= 14.39.0 ? ... OK (14.39.0)
Running /opt/gitlab/embedded/service/gitlab-shell/bin/gitlab-shell-check
Internal API available: OK
Redis available via internal API: OK
gitlab-shell self-check successful


Checking GitLab Shell ... Finished


Checking Gitaly ...


Gitaly: ... default ... OK


Checking Gitaly ... Finished


Checking Sidekiq ...


Sidekiq: ... Running? ... yes
Number of Sidekiq processes (cluster/worker) ... 1/1


Checking Sidekiq ... Finished


Checking Incoming Email ...


Incoming Email: ... Reply by email is disabled in config/gitlab.yml


Checking Incoming Email ... Finished


Checking LDAP ...


LDAP: ... LDAP is disabled in config/gitlab.yml


Checking LDAP ... Finished


Checking GitLab App ...


Database config exists? ... yes
Tables are truncated? ... skipped
All migrations up? ... yes
Database contains orphaned GroupMembers? ... no
GitLab config exists? ... yes
GitLab config up to date? ... yes
Cable config exists? ... yes
Resque config exists? ... yes
Log directory writable? ... yes
Tmp directory writable? ... yes
Uploads directory exists? ... yes
Uploads directory has correct permissions? ... yes
Uploads directory tmp has correct permissions? ... skipped (no tmp uploads folder yet)
Systemd unit files or init script exist? ... skipped (omnibus-gitlab has neither init script nor systemd units)
Systemd unit files or init script up-to-date? ... skipped (omnibus-gitlab has neither init script nor systemd units)
Projects have namespace: ...
2/1 ... yes
Redis version >= 6.2.14? ... yes
Ruby version >= 3.0.6 ? ... yes (3.2.5)
Git user has default SSH configuration? ... yes
Active users: ... 4
Is authorized keys file accessible? ... yes
GitLab configured to store new projects in hashed storage? ... yes
All projects are in hashed storage? ... yes
Elasticsearch version 7.x-8.x or OpenSearch version 1.x ... skipped (Advanced Search is disabled)
All migrations must be finished before doing a major upgrade ... skipped (Advanced Search is disabled)


Checking GitLab App ... Finished


Checking GitLab subtasks ... Finished
Edited by Rohit Shambhuni