An openssl security update has been released for Debian GNU/Linux 10 to address an overflow bug, which could result in denial of service.

DSA 4855-1: openssl security update

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Debian Security Advisory DSA-4855-1 security@debian.org
  https://www.debian.org/security/ Salvatore Bonaccorso
February 17, 2021   https://www.debian.org/security/faq
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Package : openssl
CVE ID : CVE-2019-1551 CVE-2021-23840 CVE-2021-23841
Debian Bug : 947949

Multiple vulnerabilities have been discovered in OpenSSL, a Secure
Sockets Layer toolkit. An overflow bug in the x64_64 Montgomery squaring
procedure, an integer overflow in CipherUpdate and a NULL pointer
dereference flaw X509_issuer_and_serial_hash() were found, which could
result in denial of service.

Additional details can be found in the upstream advisories
  https://www.openssl.org/news/secadv/20191206.txt and
  https://www.openssl.org/news/secadv/20210216.txt .

For the stable distribution (buster), these problems have been fixed in
version 1.1.1d-0+deb10u5.

We recommend that you upgrade your openssl packages.

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

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/