A grub2 regression update has been released for Debian GNU/Linux 10 to fix a boot-regression when chainloading another bootlaoder and breaking notably dual-boot with Windows.

DSA 4735-2: grub2 regression update

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Debian Security Advisory DSA-4735-2 security@debian.org
  https://www.debian.org/security/ Salvatore Bonaccorso
July 30, 2020   https://www.debian.org/security/faq
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Package : grub2
Debian Bug : 966554

The update for grub2 released as DSA 4735-1 caused a boot-regression
when chainloading another bootlaoder and breaking notably dual-boot with
Windows. Updated grub2 packages are now available to correct this issue.

For the stable distribution (buster), this problem has been fixed in
version 2.02+dfsg1-20+deb10u2.

We recommend that you upgrade your grub2 packages.

For the detailed security status of grub2 please refer to its security
tracker page at:
  https://security-tracker.debian.org/tracker/grub2

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