The mpi_powm function in Libgcrypt before 1.6.3 and GnuPG before 1.4.19 allows attackers to obtain sensitive information by leveraging timing differences when accessing a pre-computed table during modular exponentiation, related to a "Last-Level Cache Side-Channel Attack."
https://lists.gnupg.org/pipermail/gnupg-announce/2015q1/000364.html
https://lists.gnupg.org/pipermail/gnupg-announce/2015q1/000363.html
https://ieeexplore.ieee.org/document/7163050