Technical Tip: Blocking clients that are not compliant with RFC 9155

Description

This article describes how to make FortiADC stop TLS handshakes with clients that are sending MD5 or SHA-1 in the signature_algorithms extension in the TLS handshake as per the RFC 9155 requirements.

Solution

FortiADC version 8.0.3 and above.

Solution

Modify the client SSL profile using the CLI to state the allowed signature algorithms and be sure not to include SHA-1 or MD5.

Add the list required under 'set sigalgs', but do not include any of the ones that include SHA1 or MD5.

config load-balance client-ssl-profile
    edit <name>
        set sigalgs <list>
    next
end

Example:

config load-balance client-ssl-profile
    edit client-profile-test
        set sigalgs ecdsa_secp256r1_sha256 ecdsa_secp384r1_sha384 ecdsa_secp521r1_sha512 rsa_pss_pss_sha256 rsa_pss_pss_sha384 rsa_pss_pss_sha512 rsa_pss_rsae_sha256 rsa_pss_rsae_sha384 rsa_pss_rsae_sha512 rsa_pkcs1_sha256 rsa_pkcs1_sha384 rsa_pkcs1_sha512 mldsa44 mldsa65 mldsa87 ecdsa_sha224 rsa_pkcs1_sha224
    next
end

Note: Do not include any algorithms with sha1 or mds in the client ssl profile.

For more information on the command, see the FortiADC's config load-balance client-ssl-profile.