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[R2] Check_MK Multisite Web UI Stored and Reflected XSS



An internal server error can be triggered on the Check_MK Multisite web interface by providing an unexpected format to the output_format parameter. The internal server error page will then display output from the Apache error log. A remote unauthenticated attacker can introduce both reflected and stored HTML/Javascript to the error log using the output_format parameter or by the username in a failed HTTP basic authentication login attempt.

For example, visiting the following URL on an affected target will create a popup box. The target will also persist the code in the Apache error log so that the next user to view the internal server error page will also see the popup.



The vendor has released Check_MK versions 1.2.8p25 and 1.4.0p9 to address this issue.

Disclosure Timeline

2017-06-28 - Issue discovered
2017-07-04 - Disclosed to security at check-mk.org
2017-07-06 - Team at Check_MK confirm vulnerability, introduce fix for next release.
2017-07-24 - Fixed release 1.4.0p9 added to check-mk.org
2017-07-25 - Fixed release 1.2.8p25 added to check-mk.org
2017-08-16 - CVE requested / received

All information within TRA advisories is provided “as is”, without warranty of any kind, including the implied warranties of merchantability and fitness for a particular purpose, and with no guarantee of completeness, accuracy, or timeliness. Individuals and organizations are responsible for assessing the impact of any actual or potential security vulnerability.

Tenable takes product security very seriously. If you believe you have found a vulnerability in one of our products, we ask that you please work with us to quickly resolve it in order to protect customers. Tenable believes in responding quickly to such reports, maintaining communication with researchers, and providing a solution in short order.

For more details on submitting vulnerability information, please see our Vulnerability Reporting Guidelines page.

If you have questions or corrections about this advisory, please email [email protected]

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