A flaw was found in the way HAProxy processed HTTP responses containing the "Set-Cookie2" header. This flaw could allow an attacker to send crafted HTTP response packets which lead to an infinite loop, eventually resulting in a denial of service condition. The highest threat from this vulnerability is availability.
Apparently unreleased patch: https://github.com/haproxy/haproxy/commit/bfb15ab34ead85f64cd6da0e9fb418c9cd14cee8
Fixed versions are already in the tree.
If you want to stabilize, please stabilize: