Security Considerations

Table of Contents

Introduction

Tomcat is configured to be reasonably secure for most use cases by default. Some environments may require more, or less, secure configurations. This page is to provide a single point of reference for configuration options that may impact security and to offer some commentary on the expected impact of changing those options. The intention is to provide a list of configuration options that should be considered when assessing the security of a Tomcat installation.

Note: Reading this page is not a substitute for reading and understanding the detailed configuration documentation. Fuller descriptions of these attributes may be found in the relevant documentation pages.

Non-Tomcat settings

Tomcat configuration should not be the only line of defense. The other components in the system (operating system, network, database, etc.) should also be secured.

Tomcat should not be run under the root user. Create a dedicated user for the Tomcat process and provide that user with the minimum necessary permissions for the operating system. For example, it should not be possible to log on remotely using the Tomcat user.

File permissions should also be suitably restricted. In the .tar.gz distribution, files and directories are not world readable and the group does not have write access. On Unix like operating systems, Tomcat runs with a default umask of 0027 to maintain these permissions for files created while Tomcat is running (e.g. log files, expanded WARs, etc.).

Taking the Tomcat instances at the ASF as an example (where auto-deployment is disabled and web applications are deployed as exploded directories), the standard configuration is to have all Tomcat files owned by root with group Tomcat and whilst owner has read/write privileges, group only has read and world has no permissions. The exceptions are the logs, temp and work directory that are owned by the Tomcat user rather than root. This means that even if an attacker compromises the Tomcat process, they can't change the Tomcat configuration, deploy new web applications or modify existing web applications. The Tomcat process runs with a umask of 007 to maintain these permissions.

At the network level, consider using a firewall to limit both incoming and outgoing connections to only those connections you expect to be present.

JMX

The security of the JMX connection is dependent on the implementation provided by the JRE and therefore falls outside the control of Tomcat.

Typically, access control is very limited (either read-only to everything or read-write to everything). Tomcat exposes a large amount of internal information and control via JMX to aid debugging, monitoring and management. Given the limited access control available, JMX access should be treated as equivalent to local root/admin access and restricted accordingly.

The JMX access control provided by most (all?) JRE vendors does not log failed authentication attempts, nor does it provide an account lock-out feature after repeated failed authentications. This makes a brute force attack easy to mount and difficult to detect.

Given all of the above, care should be taken to ensure that, if used, the JMX interface is appropriately secured. Options you may wish to consider to secure the JMX interface include:

  • configuring a strong password for all JMX users;
  • binding the JMX listener only to an internal network;
  • limiting network access to the JMX port to trusted clients; and
  • providing an application specific health page for use by external monitoring systems.

Default web applications

General

Tomcat ships with a number of web applications that are enabled by default. Vulnerabilities have been discovered in these applications in the past. Applications that are not required should be removed so the system will not be at risk if another vulnerability is discovered.

ROOT

The ROOT web application presents a very low security risk but it does include the version of Tomcat that is being used. The ROOT web application should normally be removed from a publicly accessible Tomcat instance, not for security reasons, but so that a more appropriate default page is shown to users.

Documentation

The documentation web application presents a very low security risk but it does identify the version of Tomcat that is being used. It should normally be removed from a publicly accessible Tomcat instance.

Examples

The examples web application should always be removed from any security sensitive installation. While the examples web application does not contain any known vulnerabilities, it is known to contain features (particularly the cookie examples that display the contents of all received and allow new cookies to be set) that may be used by an attacker in conjunction with a vulnerability in another application deployed on the Tomcat instance to obtain additional information that would otherwise be unavailable.

Manager

The Manager application allows the remote deployment of web applications and is frequently targeted by attackers due to the widespread use of weak passwords and publicly accessible Tomcat instances with the Manager application enabled. The Manager application is not accessible by default as no users are configured with the necessary access. If the Manager application is enabled then guidance in the section Securing Management Applications section should be followed.

Host Manager

The Host Manager application allows the creation and management of virtual hosts - including the enabling of the Manager application for a virtual host. The Host Manager application is not accessible by default as no user