VA-003 Compare and configure secrets engines Practice Question
An administrator enables the database secrets engine for PostgreSQL. After configuring the connection, running `vault write database/config/someconfig` yields error: 'x509: certificate signed by unknown authority'. What is the most likely cause?
⚠ Common exam trap
HashiCorp often tests the distinction between TLS errors related to the target server's certificate (outbound connection) versus the Vault server's own certificate (inbound connection), causing candidates to confuse the direction of the TLS handshake.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The PostgreSQL server's TLS certificate is not trusted by Vault's CA bundle
The error 'x509: certificate signed by unknown authority' indicates that Vault, when connecting to the PostgreSQL database, received a TLS certificate from the server that was not signed by any Certificate Authority (CA) present in Vault's trusted CA bundle. Vault uses its system's CA pool or a custom CA bundle configured in the connection string to verify the database server's certificate. If the PostgreSQL server uses a self-signed certificate or one issued by an internal CA not trusted by Vault, this error occurs. Option B correctly identifies that the PostgreSQL server's TLS certificate is not trusted by Vault's CA bundle.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The connection string is incorrect
Why it's wrong here
A malformed connection string typically yields a parse, host-resolution or authentication failure, not an x509 unknown-authority trust error, which indicates the server certificate's issuer is untrusted. It is tempting because connection details are commonly misconfigured, but that would be correct for a wrong hostname, port or credentials.
- ✓
The PostgreSQL server's TLS certificate is not trusted by Vault's CA bundle
Why this is correct
Vault verifies the PostgreSQL server's TLS certificate against its own CA bundle during connection setup. An untrusted or self-signed certificate produces exactly this x509 error, satisfying the stem's failure at config-write time, before any credential or role logic executes.
- ✗
The database engine is not enabled
Why it's wrong here
The engine was already enabled, since the write reached connection configuration and returned a TLS trust error; a disabled engine would produce a mount or path error instead. It is tempting because enabling the secrets engine is a prerequisite step, but that would be the answer if the path itself were unrecognised.
- ✗
The Vault server's TLS certificate is self-signed
Why it's wrong here
Vault's own listener certificate is irrelevant here; the error concerns the PostgreSQL server's certificate chain, which Vault cannot verify against its trusted CAs. It is tempting because self-signed certificates are a frequent TLS culprit, but that would be correct if clients connecting to Vault itself rejected its certificate.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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