# TYPO3 extensions¶

As already mentioned above, most of the security issues have been discovered in TYPO3 extensions, not in the TYPO3 Core . Due to the fact that everybody can publish an extension in the TYPO3 repository, you never know how savvy and experienced the programmer is and how the code was developed from a security perspective.

The following sections deal with extensions in general, the risks and the basic countermeasures to address security related issues.

## Stable and reviewed extensions¶

Only a small percentage of the extensions available in the TER have been reviewed by the TYPO3 Security team. This does not imply that extensions without such an audit are insecure, but they probably have not been checked for potential security issues by an independent 3rd party (such as the TYPO3 Security Team).

The status of an extension (alpha, beta, stable, etc.) should also give you an indication in which state the developer claims the extension is. However, this classification is an arbitrary setting by the developer and may not reflect the real status and/or opinions of independent parties.

Always keep in mind that an extension may not perform the functionality that it pretends to do: An attacker could write an extension that contains malicious code or functions and publish it under a promising name. It is also possible that a well-known, harmless extension will be used for an attack in the future by introducing malicious code with an update. In a perfect world, every updated version would be reviewed and checked, but it is understandable that this approach is unlikely to be practical in most installations.

Following the guidelines listed below would improve the level of security, but the trade-off would be more effort in maintaining your website and a delay of updating existing extensions, which would possibly be against the react quickly paradigm. Thus, it depends on the specific case and project, and the intention of listing the points below is more to raise the awareness of possible risks.

• Do not install extensions or versions marked as alpha or obsolete: The developer classified the code as a early version, preview, prototype, proof-of-concept and/or as not maintained – nothing you should install on a production site.
• Be very careful when using extensions or versions marked as beta: According to the developer, this version of the extension is still in development, so it is unlikely that any security-related tests or reviews have been undertaken so far.
• Be careful with extensions and versions marked as stable, but not reviewed by the TYPO3 Security Team.
• Check every extension and extension update before you install it on a production site and review it in regards to security, see Use staging servers for developments and tests.

## Executable binaries shipped with extensions¶

TYPO3 extensions (.zip files) are packages, which may contain any kind of data/files. This can be readable PHP or Javascript source code, as well as binary files like compiled executables, e.g. Unix/Linux ELF files or Microsoft Windows .exe files.

Executing these files on a server is a security risk, because it can not be verified what these files really do (unless they are reverse-engineered or dissected likewise). Thus it is highly recommended not to use any TYPO3 extensions, which contain executable binaries. Binaries should only come from trusted and/or verified sources such as the vendor of your operating system - which also ensures, these binaries get updated in a timely manner, if a security vulnerability is discovered in these components.

## Remove unused extensions and other code¶

TYPO3 distinguishes between “imported” and “loaded” extensions. Imported extensions exist in the system and are ready to be integrated into TYPO3 but they are not installed yet. Loaded extensions are available for being used (or are being used automatically, depending on their nature), so they are “installed”.

A dangerous and loaded extension is able to harm your system in general because it becomes part of the system (functions are integrated into the system at runtime). Even extensions which are not loaded (but only “imported”) include a kind of risk because their code may contain malicious or vulnerable functions which in theory could be used to attack the system.

As a general rule, it is highly recommended you remove all code from the system that is not in use. This includes TYPO3 extensions, any TypoScript (see below), PHP scripts as well as all other functional components. In regards to TYPO3 extensions, you should remove unused extensions from the system (not only unload/deinstall them). The Extension Manager offers an appropriate function for this - an administrator backend account is required.

## Low-level extensions¶

So called “low-level” extensions provide “questionable” functionality to a level below what a standard CMS would allow you to access. This could be for example direct read/write access to the file system or direct access to the database (see Guidelines for System Administrators: Database access). If a TYPO3 integrator or a backend user (e.g. an editor) depends on those extensions, it is most likely that a misconfiguration of the system exists in general.

TYPO3 extensions like phpMyAdmin, various file browser/manager extensions, etc. may be a good choice for a development or test environment but are definitely out of place at production sites.

Extensions that allow editors to include PHP code must be avoided, too.

## Check for extension updates regularly¶

The importance of the knowledge that security updates are available has been discussed above (see TYPO3 security-bulletins). It is also essential to know how to check for extension updates: the Extension Manager (EM) is a TYPO3 backend module accessible for backend users with administrator privileges. A manual check for extension updates is available in this module.

The EM uses a cached version of the extension list from the TYPO3 Extension Repository (TER) to compare the extensions currently installed and the latest versions available. Therefore, you should retrieve an up-to-date version of the extension list from TER before checking for updates.

If extension updates are available, they are listed together with a short description of changes (the “upload comment” provided by the extension developers) and you can download/install the updates if desired. Please note that under certain circumstances, new versions may behave differently and a test/review is sometimes useful, depending on the nature and importance of your TYPO3 instance. Often a new version of an extension published by the developer is not security-related.

A scheduler task is available that lets you update the extension list automatically and periodically (e.g. once a day). In combination with the task “System Status Update (reports)”, it is possible to get a notification by email when extension updates are available.