We are following our security policy to release stable and maintenance releases concurrently in response to a security vulnerability. Details of the vulnerability will be shared on Monday 2 June, providing everyone time to update.
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GeoServer Project Steering Committee
After discussion between security researchers last week issue was downgraded from critical to high. So we had a slightly more urgent response (release stable and maintenance branches concurrently).
We advise everyone to stay up today, and release announcements that address security vulnerabilities are clearly indicated.