An openssl security update has been released for Debian GNU/Linux 9 and 10 to address multiple vulnerabilities.

DSA 4963-1: openssl security update

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Debian Security Advisory DSA-4963-1 security@debian.org
  https://www.debian.org/security/ Salvatore Bonaccorso
August 24, 2021   https://www.debian.org/security/faq
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Package : openssl
CVE ID : CVE-2021-3711 CVE-2021-3712

Multiple vulnerabilities have been discovered in OpenSSL, a Secure
Sockets Layer toolkit.

CVE-2021-3711

John Ouyang reported a buffer overflow vulnerability in the SM2
decryption. An attacker able to present SM2 content for
decryption to an application can take advantage of this flaw to
change application behaviour or cause the application to crash
(denial of service).

CVE-2021-3712

Ingo Schwarze reported a buffer overrun flaw when processing ASN.1
strings in the X509_aux_print() function, which can result in denial
of service.

Additional details can be found in the upstream advisory:
  https://www.openssl.org/news/secadv/20210824.txt

For the oldstable distribution (buster), these problems have been fixed
in version 1.1.1d-0+deb10u7.

For the stable distribution (bullseye), these problems have been fixed in
version 1.1.1k-1+deb11u1.

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/