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.
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.