Versions mentioned in the description apply to the upstream
Remediation section below for
Debian:9 relevant versions.
Libgcrypt before 1.8.8 and 1.9.x before 1.9.3 mishandles ElGamal encryption because it lacks exponent blinding to address a side-channel attack against mpi_powm, and the window size is not chosen appropriately. This, for example, affects use of ElGamal in OpenPGP.
libgcrypt20 to version 1.7.6-2+deb9u4 or higher.