Description
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.
Remediation
References
https://bugzilla.redhat.com/show_bug.cgi?id=CVE-2017-2666
https://www.debian.org/security/2017/dsa-3906
https://access.redhat.com/errata/RHSA-2017:3458
https://access.redhat.com/errata/RHSA-2017:3456
https://access.redhat.com/errata/RHSA-2017:3455
https://access.redhat.com/errata/RHSA-2017:3454
https://access.redhat.com/errata/RHSA-2017:1412
https://access.redhat.com/errata/RHSA-2017:1411
https://access.redhat.com/errata/RHSA-2017:1410
http://www.securityfocus.com/bid/98966
http://rhn.redhat.com/errata/RHSA-2017-1409.html