The IIS/ISAPI specific code in the Apache Tomcat JK ISAPI Connector 1.2.0 to 1.2.42 that normalised the requested path before matching it to the URI-worker map did not handle some edge cases correctly. If only a sub-set of the URLs supported by Tomcat were exposed via IIS, then it was possible for a specially constructed request to expose application functionality through the reverse proxy that was not intended for clients accessing Tomcat via the reverse proxy.
Use CWE-22, Apache vendor hub and Tomcat Jk Connector product page to widen CVE-2018-1323 into its surrounding weakness, vendor, and product context.
Compare it with CVE-2016-6808 and CVE-2018-11759 for nearby disclosures in the same product family.