FriendsOfFlarum OAuth: Unauthenticated account takeover via unverified email trust in Discord OAuth provider

Summary

FriendsOfFlarum OAuth allows users to log in to Flarum with GitHub, Twitter, Facebook, and other providers. Prior to 1.7.4 and 2.0.0-beta.4, the Discord OAuth provider does not check the verified field returned for an OAuth email before passing the address to Flarum core as trusted through provideTrustedEmail(). When Discord sign-in is enabled, an unauthenticated attacker who knows the email address of a Flarum user can configure a Discord account with that unverified address and a verified phone number, then sign in to cause Flarum to match the trusted address, link the attacker-controlled Discord identity to the existing user, and authenticate as the victim without a password or victim interaction. Exploitation requires that the victim's email address is not already associated with a Discord account, and it can compromise administrator accounts. Other bundled providers were not confirmed to be practically exploitable by this method because their relevant authentication flows return only verified or confirmed email addresses. This issue is fixed in versions 1.7.4 and 2.0.0-beta.4.

Timeline

1. Sep 25, 2026, 3:53 PM UTCCVE published
2. Sep 29, 2026, 7:20 PM UTCCISA SSVC assessment

   Exploitation: none · Automatable: yes · Technical impact: total

3. Sep 29, 2026, 7:21 PM UTCRecord last updated

Affected versions

• FriendsOfFlarum oauth

  fixed in 1.7.4; From 2.0.0-beta.1 · fixed in 2.0.0-beta.4

• fof/oauthPackagist

  fixed in 1.7.4

• fof/oauthPackagist

  From 2.0.0-beta.1 · fixed in 2.0.0-beta.4

References 5