Hoppscotch is an API development ecosystem. In self-hosted deployments of hoppscotch-backend from version 2026.4.1 and earlier, the unauthenticated POST /v1/onboarding/config endpoint is vulnerable to mass assignment. The global NestJS ValidationPipe is configured without whitelist: true, so extra properties on the request body that are not declared in SaveOnboardingConfigRequest are not stripped and are iterated in the service layer as if they were legitimate InfraConfig entries. Because keys such as JWT_SECRET and SESSION_SECRET are valid InfraConfigEnum values and are not explicitly rejected during validation, an unauthenticated attacker who can reach a fresh instance before onboarding completes (or when no users exist) can overwrite these values in the database. Overwriting JWT_SECRET gives the attacker control of the JWT signing key, allowing them to forge tokens for any user, including administrators, and results in full server compromise. The issue is fixed in hoppscotch 2026.5.0.

The vulnerability affects hoppscotch’s self-hosted backend component, specifically instances running hoppscotch-backend versions 2026.4.1 and earlier.

The CVSS score of 10 indicates a critical severity. The endpoint is an unauthenticated POST, giving an attacker a remote network exploitation vector if they can reach a fresh or empty instance. The EPSS score of < 1% suggests a low current exploitation probability, but the high CVSS score and lack of authentication mean the vulnerability is potentially highly exploitable when conditions are met. The vulnerability is not listed in the CISA KEV catalog.