An information leak vulnerability was discovered in HAProxy 2.1, 2.2 before 2.2.27, 2.3, 2.4 before 2.4.21, 2.5 before 2.5.11, 2.6 before 2.6.8, 2.7 before 2.7.1. There are 5 bytes left uninitialized in the connection buffer when encoding the FCGIBEGINREQUEST record. Sensitive data may be disclosed to configured FastCGI backends in an unexpected way.

https://git.haproxy.org/?p=haproxy.git;a=commitdiff;h=2e6bf0a

A flaw was found in HAProxy's headers processing that causes HAProxy to drop important headers fields such as Connection, Content-length, Transfer-Encoding, and Host after having partially processed them. A maliciously crafted HTTP request could be used in an HTTP request smuggling attack to bypass filtering and detection by HAProxy.