SigNoz before 0.143.0 Authentication Bypass via Empty JWT Secret

SigNoz from v0.8.0 before v0.143.0 defaults the JWT tokenizer signing secret (tokenizer::jwt::secret, set via SIGNOZ_TOKENIZER_JWT_SECRET or the deprecated SIGNOZ_JWT_SECRET) to an empty string, and Config.Validate() does not reject the empty value, so a deployment that does not configure a secret starts up and both signs and verifies session tokens with an empty HMAC key. Because the JWT tokenizer was the default provider, any such deployment is affected. An unauthenticated attacker who knows the ID of an existing user can forge a valid session token for that user — including an administrator — by signing the id, orgId and email claims with an empty key; the organization ID (and whether an email is registered) can be obtained without authentication from /api/v2/sessions/context. A forged refresh token can be exchanged at /api/v2/sessions/rotate for a new token pair and cannot be revoked, so it remains usable for its full lifetime (30 days by default). Fixed in v0.143.0, which requires a JWT secret when the jwt provider is selected and changes the default provider to opaque.