Apache Tomcat is the leading Java application server by market share and the world's most widely used web application server overall. Currently at version 8, the popular web server has not been without its security flaws, perhaps most famously publicized in this incident of aircraft hacking by security researcher Chris Roberts earlier this year. However, hardening Tomcat's default configuration is just plain good security sense—even if you don't plan on using it on your plane's network. The following are 15 way to secure Apache Tomcat 8, out-of-the-box.
Table of contents
- Don't run Tomcat as the root user
- Remove any default sample or test web applications
- Put Tomcat's shutdown procedure on lockdown
- Disable support for TRACE requests
- Disable sending of the X-Powered-By HTTP header
- Disable SSLv3 to prevent POODLE attacks
- Set the deployXML attribute to false in a hosted environment
- Configure and use realms judiciously
- Set Tomcat to create new facade object for each request
- Ensure that access to resources is set to read-only
- Disable Tomcat from displaying directory listings
- Enable logging of network traffic
- Disable automated deployment if not in use
- Disable or limit the Tomcat Manager Webapp
- Limit the availability of connectors
1. Don't run Tomcat as the root user
This line of advice applies to most web server platforms. Web-related services should not be run by user accounts with a high level of administrative access. In Tomcat's case, a user with the minimum necessary OS permissions should be created exclusively to run the Tomcat process.
2. Remove any default sample or test web applications
Most web server platforms also provide a set of sample or test web application for demo and learning purposes. These applications have been known to harbor vulnerabilities, and should be removed if not in use. Tomcat's examples web application is an application that should be removed to prevent exploitation.
3. Put Tomcat's shutdown procedure on lockdown
This prevents malicious actors from shutting down Tomcat's web services. Either disable the shutdown port by setting the port attribute in the server.xml file to -1. If the port must be kept open, be sure to configure a strong password for shutdown.
4. Disable support for TRACE requests
Though useful for debugging, enabling allowTrace can expose some browsers to an cross-site scripting XSS attack. This can be mitigated by disabling allowTrace in the server.xml file.
5. Disable sending of the X-Powered-By HTTP header
If enabled, Tomcat will send information such as the Servlet and JSP specification versions and the full Tomcat version, among others. This gives attackers a workable starting point to craft an attack. To prevent this information leakage, disable the xpoweredBy attribute in the server.xml file.
6. Disable SSLv3 to prevent POODLE attacks
POODLE is a SSL v3 protocol vulnerability discovered in 2014. An attacker can gain access to sensitive information such as passwords and browser cookies by exploiting this vulnerability; subsequently, SSL v3 (and SSL in general) should not be included in server.xml file under the sslEnabledProtocols attribute.
7. Set the deployXML attribute to false in a hosted environment
The prevents would-be attackers from attempting to increase privileges to a web application by packaging an altered/custom context.xml. This is especially critical in hosted environments where other web applications sharing the same server resources cannot be trusted.
8. Configure and use realms judiciously
Tomcat's realms are designed differently and their limitations should be understood before use. For example, the DataSourceRealm should be used in place of the JDBCRealm, as the latter is single threaded for all authentication/authorization options and not suited for production use. The JAASRealm should also be avoided, as it is seldom used and sports an immature codebase.
9. Set Tomcat to create new facade object for each request
This can be configured by setting the org.apache.catalina.connector.RECYCLE_FACADES system property to true. By doing this, you reduce the chance of a buggy application exposing data between requests.
10. Ensure that access to resources is set to read-only
This can be done by setting readonly to true under DefaultServlet, effectively preventing clients from deleting/modifying static resources on the server and uploading new resources.
11. Disable Tomcat from displaying directory listings
Listing the contents of directories with a large number of files can consume considerable system resources, and can therefore be used in a denial-of-service (DoS) attack. Setting listings to false under DefaultServlet mitigates this risk.
12. Enable logging of network traffic
In general, logs should generated and maintained on all levels (e.g., user access, Tomcat internals, et al), but network traffic logging is especially useful for breach assessment and forensics. To set up your Tomcat application to create logs of network traffic, use/configure the AccessLogValve component.
13. Disable automated deployment if not in use
If you're running a fully-realized CI/CD pipeline, good for you—you'll need full use of Tomcat's host components. However, if not—be sure to set all the host attributes to false (autoDeploy, deployOnStartup, and deployXML) to prevent them from being compromised by an attacker.
14. Disable or limit the Tomcat Manager Webapp
Tomcat Manager enables easy configuration and management of Tomcat instances through one web interface. Convenient, no doubt—for both authorized administrators and attackers. Alternative methods for administering Tomcat instances are therefore better, but if Tomcat Manager must be used, be sure to use its configuration options to limit your risk exposure.
15. Limit the availability of connectors
Connectors by default listen to all interfaces. For better security, they should only listen to those required by your web application and ignore the rest. This can be accomplished by setting the address attribute of the connector element.
In short, Apache Tomcat's popularity invariably means that its vulnerabilities and exploits are well known by both security professionals and malicious actors alike. Out-of-the-box security is never sufficient for protecting against today's cyber threats, and proper hardening of Tomcat is especially critical given the server platform's ubiquity. Looking for a way to perform these hardening checks and more, automatically—with just a few mouse clicks? Check out ScriptRock's platform for vulnerability detection and security monitoring. It's free for up to 10 servers, so try it today on us.