Apache Tomcat 4.1.0 through 4.1.39, 5.5.0 through 5.5.27, and 6.0.0 through 6.0.18, when FORM authentication is used, allows remote attackers to enumerate valid usernames via requests to /j_security_check with malformed URL encoding of passwords, related to improper error checking in the (1) MemoryRealm, (2) DataSourceRealm, and (3) JDBCRealm authentication realms, as demonstrated by a % (percent) value for the j_password parameter.
Apache Tomcat 4.1.0 through 4.1.39, 5.5.0 through 5.5.27, and 6.0.0 through 6.0.18 permits web applications to replace an XML parser used for other web applications, which allows local users to read or modify the (1) web.xml, (2) context.xml, or (3) tld files of arbitrary web applications via a crafted application that is loaded earlier than the target application.
The JK Connector (aka mod_jk) 1.2.0 through 1.2.26 in Apache Tomcat allows remote attackers to obtain sensitive information via an arbitrary request from an HTTP client, in opportunistic circumstances involving (1) a request from a different client that included a Content-Length header but no POST data or (2) a rapid series of requests, related to noncompliance with the AJP protocol's requirements for requests containing Content-Length headers.