A libgcrypt20 security update has been released for Debian GNU/Linux 9 LTS to address a mishandling of ElGamal encryption results in a possible side-channel attack and an interoperability problem with keys not generated by GnuPG/libgcrypt.

DLA 2691-1: libgcrypt20 security update

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Debian LTS Advisory DLA-2691-1 debian-lts@lists.debian.org
  https://www.debian.org/lts/security/ Thorsten Alteholz
June 25, 2021   https://wiki.debian.org/LTS
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Package : libgcrypt20
Version : 1.7.6-2+deb9u4
CVE ID : CVE-2021-33560

An issue has been found in libgcrypt20, a crypto library.
Mishandling of ElGamal encryption results in a possible side-channel
attack and an interoperability problem with keys not generated by
GnuPG/libgcrypt.

For Debian 9 stretch, this problem has been fixed in version
1.7.6-2+deb9u4.

We recommend that you upgrade your libgcrypt20 packages.

For the detailed security status of libgcrypt20 please refer to
its security tracker page at:
  https://security-tracker.debian.org/tracker/libgcrypt20

Further information about Debian LTS security advisories, how to apply
these updates to your system and frequently asked questions can be
found at:   https://wiki.debian.org/LTS