The Realm implementations in Apache Tomcat versions 9.0.0.M1 to 9.0.0.M9, 8.5.0 to 8.5.4, 8.0.0.RC1 to 8.0.36, 7.0.0 to 7.0.70 and 6.0.0 to 6.0.45 did not process the supplied password if the supplied user name did not exist. This made a timing attack possible to determine valid user names. Note that the default configuration includes the LockOutRealm which makes exploitation of this vulnerability harder.
rhn.redhat.com/errata/RHSA-2017-0457.html
www.debian.org/security/2016/dsa-3720
www.securityfocus.com/bid/93939
www.securitytracker.com/id/1037144
access.redhat.com/errata/RHSA-2017:0455
access.redhat.com/errata/RHSA-2017:0456
access.redhat.com/errata/RHSA-2017:2247
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security.netapp.com/advisory/ntap-20180605-0001/
usn.ubuntu.com/4557-1/
www.oracle.com//security-alerts/cpujul2021.html
www.oracle.com/security-alerts/cpuoct2021.html