A haproxy security update has been released for Debian GNU/Linux 11 to address several vulnerabilities.

DSA 4960-1: haproxy security update

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Debian Security Advisory DSA-4960-1 security@debian.org
  https://www.debian.org/security/ Salvatore Bonaccorso
August 17, 2021   https://www.debian.org/security/faq
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Package : haproxy
CVE ID : not yet assigned

Several vulnerabilities were discovered in HAProxy, a fast and reliable
load balancing reverse proxy, which can result in HTTP request
smuggling. By carefully crafting HTTP/2 requests, it is possible to
smuggle another HTTP request to the backend selected by the HTTP/2
request. With certain configurations, it allows an attacker to send an
HTTP request to a backend, circumventing the backend selection logic.

Known workarounds are to disable HTTP/2 and set
"tune.h2.max-concurrent-streams" to 0 in the "global" section.

global
tune.h2.max-concurrent-streams 0

For the stable distribution (bullseye), these problems have been fixed in
version 2.2.9-2+deb11u1.

We recommend that you upgrade your haproxy packages.

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

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/