It was discovered in Undertow that the code that parsed the HTTP request line permitted invalid characters. This could be exploited, in conjunction with a proxy that also permitted the invalid characters but with a different interpretation, to inject data into the HTTP response. By manipulating the HTTP response the attacker could poison a web-cache, perform an XSS attack, or obtain sensitive information from requests other than their own.
rhn.redhat.com/errata/RHSA-2017-1409.html
www.securityfocus.com/bid/98966
access.redhat.com/errata/RHSA-2017:1410
access.redhat.com/errata/RHSA-2017:1411
access.redhat.com/errata/RHSA-2017:1412
access.redhat.com/errata/RHSA-2017:3454
access.redhat.com/errata/RHSA-2017:3455
access.redhat.com/errata/RHSA-2017:3456
access.redhat.com/errata/RHSA-2017:3458
bugzilla.redhat.com/show_bug.cgi?id=CVE-2017-2666
www.debian.org/security/2017/dsa-3906