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
github.com/apache/tomcat
github.com/apache/tomcat/commit/86b2e436099cb48f30dad950175c5beeeb763756
github.com/apache/tomcat/commit/970e615c7ade6ec6c341470bbc76aa1256353737
github.com/apache/tomcat/commit/d79c63d424fe6b225678416343b9ce106dec947c
github.com/apache/tomcat80/commit/dc4c3317452f0bc2c5e1f6a08d3bd9f22488b450
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nvd.nist.gov/vuln/detail/CVE-2016-0762
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