A curl security update has been released for Debian GNU/Linux 9 LTS to address two security issues.

DLA 2773-1: curl security update

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Debian LTS Advisory DLA-2773-1 debian-lts@lists.debian.org
  https://www.debian.org/lts/security/ Thorsten Alteholz
September 30, 2021   https://wiki.debian.org/LTS
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Package : curl
Version : 7.52.1-5+deb9u16
CVE ID : CVE-2021-22946 CVE-2021-22947

Two issues have been found in curl, a command line tool and an easy-to-use
client-side library for transferring data with URL syntax.

CVE-2021-22946
Crafted answers from a server might force clients to not use TLS on
connections though TLS was required and expected.

CVE-2021-22947
When using STARTTLS to initiate a TLS connection, the server might
send multiple answers before the TLS upgrade and such the client
would handle them as being trusted. This could be used by a
MITM-attacker to inject fake response data.

For Debian 9 stretch, these problems have been fixed in version
7.52.1-5+deb9u16.

We recommend that you upgrade your curl packages.

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

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