| Title | Formbricks 5.0.0 Improper Access Controls |
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| Description | Unauthenticated Email Oracle via isSurveyResponsePresentAction
Summary
The `isSurveyResponsePresentAction` server action returns whether a specific email address has responded to a survey. It requires no authentication and has no rate limiting. Any unauthenticated actor who knows a public survey link can use it as a boolean oracle to determine which email addresses have responded to that survey. No authentication, no session cookie, and no rate limit. The attacker can enumerate a full email list in seconds.
Vulnerable code
`apps/web/modules/survey/link/actions.ts:62-66` and `apps/web/lib/utils/action-client/index.ts:14-48` - compare with `authenticatedActionClient` (line 51), which calls `getServerSession()` and requires a valid session. The `isSurveyResponsePresentAction` deliberately uses the unauthenticated `actionClient`.
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| Source | ⚠️ https://github.com/formbricks/formbricks/pull/8094 |
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| User | geochen (UID 78995) |
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| Submission | 06/07/2026 05:18 (29 days ago) |
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| Moderation | 07/05/2026 20:21 (29 days later) |
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| Status | Accepted |
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| VulDB entry | 376386 [Formbricks 5.0.0 Survey actions.ts access control] |
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| Points | 20 |
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