Werk #22527: Invalid rule values no longer crash the whole Check_MK service

Component	Core & setup
Title	Invalid rule values no longer crash the whole Check_MK service
Date	Oct 12, 2026
Level	Trivial Change
Class	Bug Fix
Compatibility	Compatible - no manual interaction needed
Checkmk versions & editions	3.0.0b1 Not yet released Checkmk Community, Checkmk Pro, Checkmk Ultimate, Checkmk Cloud, Checkmk Ultimate MT 2.5.0p16 Not yet released Checkmk Community, Checkmk Pro, Checkmk Ultimate, Checkmk Cloud, Checkmk Ultimate MT 2.4.0p38 Not yet released Checkmk Community, Checkmk Pro, Checkmk Ultimate, Checkmk Cloud, Checkmk Ultimate MT

If a rule contained a parameter value in a format Checkmk cannot read, for example a leftover value from a very old configuration, the "Check_MK" service of the affected host crashed. As a result, none of the services of that host were checked anymore.

Now the crash is limited to the service that uses the invalid value: that service goes to UNKNOWN and the crash report names it, instead of the "Check_MK" service. All other services of the host are checked as usual.

To get rid of the crash, open the affected rule in the setup and save it again, or recreate it. When you update a site, cmk-update-config lists such rules with the warning "Invalid rule configuration detected".

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