Attack Chain

1. The attacker identifies a target Nhost application that utilizes a vulnerable OAuth provider (Discord, Bitbucket, AzureAD, or EntraID).
2. The attacker creates an account on the chosen OAuth provider.
3. The attacker modifies their email address on the OAuth provider to match the email address of the victim's Nhost account. In the case of Discord, the attacker changes the email but skips the verification step.
4. The attacker initiates the "Sign in with [OAuth Provider]" flow on the target Nhost application.
5. Nhost's backend fetches the attacker's profile from the OAuth provider. Due to the vulnerability, Nhost incorrectly trusts the 'verified' status, even if the email is unverified.
6. Nhost locates the victim's account based on the matching email address.
7. Nhost links the attacker's OAuth provider identity to the victim's account in the database using the InsertUserProvider function.
8. Nhost generates a new session for the victim's account and provides it to the attacker, granting the attacker full access to the victim's account.

Impact

Successful exploitation allows for full account takeover of any existing Nhost user, without requiring any interaction from the victim. The attacker can then change the account email, disable other login methods, and permanently lock out the legitimate owner. This is particularly critical in applications with admin or privileged accounts, potentially leading to significant data breaches or unauthorized access to sensitive systems. The vulnerability affects Nhost versions prior to 0.0.0-20260417112436-ec8dab3f2cf4.

Recommendation

• Upgrade Nhost to a version containing the fix for this vulnerability (>= 0.0.0-20260417112436-ec8dab3f2cf4).
• Implement a controller-level guard that enforces email verification regardless of the adapter's reported EmailVerified status, as described in the "Defense-in-Depth Gap" section. This mitigates the risk of future vulnerabilities due to changes in OAuth provider APIs.
• For Discord, apply the fix described in the advisory, adding the Verified field to the discordUserProfile struct and utilizing it in the EmailVerified assignment within the providers/discord.go file.
• For Bitbucket, remove the fallback to unconfirmed emails as described in the advisory, preventing the adapter from using unverified emails in providers/bitbucket.go.
• For AzureAD and EntraID, avoid falling back to preferred_username or UPN for account-linking email, as these fields do not prove email ownership, as documented in the advisory.