The code in Apache Tomcat 9.0.0.M1 to 9.0.0.M11, 8.5.0 to 8.5.6, 8.0.0.RC1 to 8.0.38, 7.0.0 to 7.0.72, and 6.0.0 to 6.0.47 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 and/or obtain sensitive information from requests other then their own.
https://www.exploit-db.com/exploits/41783/
https://usn.ubuntu.com/4557-1/
https://tomcat.apache.org/security-9.html#Fixed_in_Apache_Tomcat_9.0.0.M13
https://tomcat.apache.org/security-8.html#Fixed_in_Apache_Tomcat_8.5.8
https://tomcat.apache.org/security-8.html#Fixed_in_Apache_Tomcat_8.0.39
https://tomcat.apache.org/security-7.html#Fixed_in_Apache_Tomcat_7.0.73
https://tomcat.apache.org/security-6.html#Fixed_in_Apache_Tomcat_6.0.48
https://security.netapp.com/advisory/ntap-20180607-0001/
https://access.redhat.com/errata/RHSA-2017:0935
https://access.redhat.com/errata/RHSA-2017:0456
https://access.redhat.com/errata/RHSA-2017:0455
http://www.securitytracker.com/id/1037332
http://www.securityfocus.com/bid/94461
http://www.oracle.com/technetwork/security-advisory/cpuoct2017-3236626.html
http://www.debian.org/security/2016/dsa-3738
http://rhn.redhat.com/errata/RHSA-2017-0527.html
http://rhn.redhat.com/errata/RHSA-2017-0457.html
http://rhn.redhat.com/errata/RHSA-2017-0250.html
http://rhn.redhat.com/errata/RHSA-2017-0247.html
http://rhn.redhat.com/errata/RHSA-2017-0246.html