In Libgcrypt before 1.7.7, an attacker who learns the EdDSA session key (from side-channel observation during the signing process) can easily recover the long-term secret key. 1.7.7 makes a cipher/ecc-eddsa.c change to store this session key in secure memory, to ensure that constant-time point operations are used in the MPI library.
https://www.oracle.com/technetwork/security-advisory/cpujan2019-5072801.html
https://bugzilla.suse.com/show_bug.cgi?id=1042326
http://www.securityfocus.com/bid/99046
http://www.oracle.com/technetwork/security-advisory/cpujul2018-4258247.html