cipher/elgamal.c in Libgcrypt through 1.8.2, when used to encrypt messages directly, improperly encodes plaintexts, which allows attackers to obtain sensitive information by reading ciphertext data (i.e., it does not have semantic security in face of a ciphertext-only attack). The Decisional Diffie-Hellman (DDH) assumption does not hold for Libgcrypt's ElGamal implementation. Reference: https://lists.gnupg.org/pipermail/gcrypt-devel/2018-February/004394.html
Created libgcrypt tracking bugs for this issue: Affects: fedora-all [bug 1543438]
Created mingw-libgcrypt tracking bugs for this issue: Affects: epel-7 [bug 1543443] Affects: fedora-all [bug 1543442]
I would not say this is a real security issue unless any application really uses El Gamal as described in the e-mail. But then it would be security issue of that application, not libgcrypt in particular.
Statement: This is not a security flaw in libgcrypt. However if an application uses The El-gamal algorithm implemented by libgcrypt in a particular way than the application would be vulnerable to security flaw(s). More detailed explanation is available at: https://lists.gnupg.org/pipermail/gcrypt-devel/2018-February/004401.html