CVE-2025-21521 is a security vulnerability in the thread pooling component of the MySQL server, as identified by Red Hat Product Security. The vulnerability is unspecified in detail but is considered important and affects Red Hat Enterprise Linux 9.2 Extended Update Support and related distributions. Red Hat has released updated MySQL packages (version 8.0.40-1.el9_2.1) to remediate this issue. The advisory does not provide a CVSS score or detailed technical exploitation information but directs users to apply the update to mitigate the risk.

The vulnerability affects the MySQL server's thread pooling functionality, which could potentially impact the stability or security of multi-threaded operations within the database server. The exact impact is not detailed, but the severity is rated as Important by Red Hat, indicating a significant security concern that warrants prompt remediation. There are no known exploits in the wild at the time of the advisory.

Red Hat has released an official security update that addresses CVE-2025-21521. Users should apply the MySQL update packages version 8.0.40-1.el9_2.1 or later for Red Hat Enterprise Linux 9.2 Extended Update Support and related variants as detailed in Red Hat Advisory RHSA-2025:1767. For detailed update instructions, refer to https://access.redhat.com/articles/11258. No additional mitigation steps are specified or required beyond applying the official update.