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CVE-2025-21566: Vulnerability in the MySQL Server product of Oracle MySQL (component: Server: Optimizer). Supported versions that are affected are 9.1.0 and prior. Easily exploitable vulnerability allows low privileged attacker with network access via multiple protocols to compromise MySQL Server. Successful attacks of this vulnerability can result in unauthorized ability to cause a hang or frequently repeatable crash (complete DOS) of MySQL Server. CVSS 3.1 Base Score 6.5 (Availability impact

mediumCVSS 6.5CVE-2025-21566

CSIRTS triage

vendor: Oracleproduct: MySQL ServerDenial of serviceaffected: 9.1.0 and prior
What
An optimizer component vulnerability allows a low-privileged attacker with network access to compromise MySQL Server.
Who is affected
All MySQL 9.1.0 and prior deployments are affected, including those with low-privilege user accounts with network access.
Urgency
Medium priority with a CVSS of 6.5; easily exploitable by low-privilege attackers and requires immediate patching.
Action
Upgrade to a patched version after 9.1.0.

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Details

Source
Microsoft Security Response Center (INTL · vendor-psirt · site)
Severity
medium — CVSS 6.5
Published
2026-08-06
Exploitation
Not in CISA KEV at last sync

Original advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2025-21566

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Referenced CVEs

CVECSIRTS overviewExternal
CVE-2025-21566coverage & exploitation statusNVD · CVE.org

Recent advisories for MySQL Server product

A cluster of recent advisories against the same product widens the attack surface — attackers routinely chain freshly published CVEs on one product, so review these together.

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