Tomcat security: Why run an exploit if you can just log in?, (Thu, Feb 5th)

In our honeypots, we recently saw a spike of requests for http://[ip address]:8080/manager/html . These requests appear to target the Apache Tomcat server. In case you havent heard of Tomcat before (unlikely): It is a Java Servlet and JavaServer Pages technology [1]. Essentially an easy way to create web applications using Java servlets. While Java may be on its way out on the client (wishful thinking…), it is still well liked and used in webapplications. The vulnerabilities being attacked by the requests above are unlikely the same buffer-overflow type vulnerabilities we worry about on the client. Instead, you will likely see standard web application exploits, and in particular attacks against weak Tomcat configurations.

In particular the URL above points to the manager web app, a web application that comes with Tomcat to allow you to manage Tomcat. Luckily it is secure by default in that there are no default users configured to use this manager web application. So you will need to add your own users. The password better be complex.

By default, passwords are not hashed or encrypted in Tomcats configuration file. However, they can be hashed. To do so, you need to edit the confserver.xml file. By default, the confserver.xml file includes a line like:

Change this to

The hashing is performedby the digest.sh script, that you can find in the tomcat bin directory. (for Windows: digest.bat). You can use this script to hash your password:

digest.sh -a SHA password

Ironically, digest.sh is just a wrapper, calling a script tools-wrapper.sh . and various SHA versions (e.g. sha-512). But it is better then keeping the password in the clear. (anybody got a link to a comprehensive documentation for this?)

Once a user is able to connect to the Application Manager, they have full access to the server in that they are able to change the configuration or upload new applications, essentially allowing them to run arbitrary code on the server.

OWASP also offers a brief guide to secure Tomcat [2] . It also doesnt hurt to check the Tomcat manual once in a while.

[1] http://tomcat.apache.org
[2]https://www.owasp.org/index.php/Securing_tomcat


Johannes B. Ullrich, Ph.D.
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