tls.legacy_key_exchange
Legacy TLS Key Exchange Only
What we check
We examine the key exchange methods the server supports. This finding is emitted when the server only offers legacy key exchange mechanisms — typically static RSA or non-ephemeral DH parameters — and does not support any modern ephemeral key exchange (ECDHE with current curves, or DHE with sufficient parameter size).
What this finding means
The server's TLS configuration uses only legacy key exchange methods. While TLS connections still work, the key exchange is weaker than current recommendations. This may indicate outdated TLS library defaults or a server that has not been reconfigured since its initial deployment.
Why it matters
- Weaker than necessary. Legacy key exchange methods may use small DH parameters or static keys that provide less security than ECDHE with modern curves.
- Forward secrecy may be absent. Static RSA key exchange provides no forward secrecy at all; small-parameter DHE provides limited protection.
- Indicator of age. A server limited to legacy key exchange is likely running outdated software or configuration that should be reviewed.
How to fix
Enable ECDHE support. For Postfix, ensure OpenSSL supports modern curves and configure:
# /etc/postfix/main.cf smtpd_tls_eecdh_grade = autoUpdate OpenSSL and the mail server to a version that supports ECDHE with X25519 or P-256 curves.
How it's graded
Legacy key exchange is an informational finding with no grading penalty. It is surfaced as a configuration signal rather than a security failure. See Grading Methodology for the full scoring model.
Evidence example
Key exchange: DHE (1024-bit parameters)
No ECDHE support detected — legacy key exchange only