TYPO3 is vulnerable to Cross-Site Scripting via frontend rendering

> ### CVSS: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:L/E:F/RL:O/RC:C (8.2)

Problem

TYPO3 core component GeneralUtility::getIndpEnv() uses the unfiltered server environment variable PATH_INFO, which allows attackers to inject malicious content.

In combination with the TypoScript setting config.absRefPrefix=auto, attackers can inject malicious HTML code into pages that have not yet been rendered and cached. As a result, injected values would be cached and delivered to other website visitors (persisted cross-site scripting).

Individual code which relies on the resolved value of GeneralUtility::getIndpEnv('SCRIPT_NAME') and corresponding usages (as shown below) are vulnerable as well.

• GeneralUtility::getIndpEnv('PATH_INFO')
• GeneralUtility::getIndpEnv('SCRIPT_NAME')
• GeneralUtility::getIndpEnv('TYPO3_REQUEST_DIR')
• GeneralUtility::getIndpEnv('TYPO3_REQUEST_SCRIPT')
• GeneralUtility::getIndpEnv('TYPO3_SITE_PATH')
• GeneralUtility::getIndpEnv('TYPO3_SITE_SCRIPT')
• GeneralUtility::getIndpEnv('TYPO3_SITE_URL')

Installations of TYPO3 versions 8.7 and 9.x are probably only affected when server environment variable TYPO3_PATH_ROOT is defined - which is the case if they were installed via Composer.

Additional investigations confirmed that Apache and Microsoft IIS web servers using PHP-CGI (FPM, FCGI/FastCGI, or similar) are affected. There might be the risk that nginx is vulnerable as well. It was not possible to exploit Apache/mod_php scenarios.

Solution

The usage of server environment variable PATH_INFO has been removed from corresponding processings in GeneralUtility::getIndpEnv(). Besides that, the public property TypoScriptFrontendController::$absRefPrefix is encoded for both being used as a URI component and for being used as a prefix in an HTML context. This mitigates the cross-site scripting vulnerability.

Update to TYPO3 versions 8.7.51 ELTS, 9.5.40 ELTS, 10.4.36 LTS, 11.5.23 LTS and 12.2.0 that fix the problem described above.

> ℹ️ Strong security defaults - Manual actions required
> Any web server using PHP-CGI (FPM, FCGI/FastCGI, or similar) needs to ensure that the PHP setting cgi.fix_pathinfo=1 is used, which is the default PHP setting. In case this setting is not enabled, an exception is thrown to avoid continuing with invalid path information.

For websites that cannot be patched timely the TypoScript setting config.absRefPrefix at least should be set to a static path value, instead of using auto - e.g. config.absRefPrefix=/ - this does not fix all aspects of the vulnerability, and is just considered to be an intermediate mitigation to the most prominent manifestation.

References

• TYPO3-CORE-SA-2023-001
• TYPO3-CORE-PSA-2023-001 pre-announcement