kubernetes/kops · error

fetched certificate is required

Error message

fetched certificate is required

What it means

Guard in validateFetchedIntermediateForSigner: the candidate certificate argument is nil, so issuer matching cannot proceed. A caller bug in the intermediate-fetch path, not attacker input.

Source

Thrown at upup/pkg/fi/cloudup/azure/attest.go:465

		return nil, fmt.Errorf("intermediate certificate from %s exceeds %d bytes", url, intermediateCertMaxResponseBytes)
	}

	cert, err := x509.ParseCertificate(body)
	if err != nil {
		return nil, fmt.Errorf("parsing intermediate certificate from %s: %w", url, err)
	}
	return cert, nil
}

// validateFetchedIntermediateForSigner checks that a fetched intermediate is actually the issuer
// referenced by the signer certificate before it is used or cached. This is a structural check
// only; the cryptographic signature is verified later by verifySignerCertChain.
func validateFetchedIntermediateForSigner(signer *x509.Certificate, cert *x509.Certificate) error {
	if signer == nil {
		return fmt.Errorf("signer certificate is required")
	}
	if cert == nil {
		return fmt.Errorf("fetched certificate is required")
	}
	if !cert.IsCA {
		return fmt.Errorf("fetched certificate is not a CA certificate")
	}
	// Require at least one issuer identifier so the per-field length guards below cannot silently
	// degrade to "no identity check" if both fields happen to be empty.
	if len(signer.RawIssuer) == 0 && len(signer.AuthorityKeyId) == 0 {
		return fmt.Errorf("signer certificate has neither RawIssuer nor AuthorityKeyId set")
	}
	if len(signer.RawIssuer) > 0 && !bytes.Equal(cert.RawSubject, signer.RawIssuer) {
		return fmt.Errorf("fetched certificate subject does not match signer issuer")
	}
	if len(signer.AuthorityKeyId) > 0 && !bytes.Equal(cert.SubjectKeyId, signer.AuthorityKeyId) {
		return fmt.Errorf("fetched certificate subject key identifier does not match signer authority key identifier")
	}

	return nil
}

View on GitHub (pinned to 4c8573c808)

Solutions

1. Fix the caller to pass the parsed (non-nil) intermediate certificate
2. Check the fetch step for how a nil certificate escaped

When it happens

Trigger: Thrown at upup/pkg/fi/cloudup/azure/attest.go:465 when the library encounters an invalid state.

Common situations: See trigger scenarios.

Understand the failure class

• SSL/TLS and certificate errors — how TLS handshakes and certificate validation fail.

AI-assisted analysis of kubernetes/kops@4c8573c808 (2026-09-05). Data as JSON: /api/errors/112f555dee061950. Report an issue: GitHub.