Key Compromise Impersonation (KCI) Vulnerability in TLS Protocol 1.2 and Earlier

CVE-2015-8960 · HIGH Severity

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

The TLS protocol 1.2 and earlier supports the rsa_fixed_dh, dss_fixed_dh, rsa_fixed_ecdh, and ecdsa_fixed_ecdh values for ClientCertificateType but does not directly document the ability to compute the master secret in certain situations with a client secret key and server public key but not a server secret key, which makes it easier for man-in-the-middle attackers to spoof TLS servers by leveraging knowledge of the secret key for an arbitrary installed client X.509 certificate, aka the "Key Compromise Impersonation (KCI)" issue.

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