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Mysql ServerDatabase / datastore · Oracle

CVE-2025-21521

HIGH · 7.5 CVSS v3.1 Published 2025-01-21
Fix available
A fix is available. Upgrade to after 9.0.1 or later.
See remediation →
84/100
Remediation priority · High
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
Vulnerability in the MySQL Server product of Oracle MySQL (component: Server: Thread Pooling). Supported versions that are affected are 8.0.39 and prior, 8.4.2 and prior and 9.0.1 and prior. Easily exploitable vulnerability allows unauthenticated 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 7.5 (Availability impacts). CVSS Vector: (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H).

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

Denial of service vulnerability in MySQL Server's Thread Pooling component. An unauthenticated attacker with network access can cause MySQL Server to hang or repeatedly crash by exploiting the thread pooling functionality.

MitigationApply Oracle MySQL security patches to upgrade to versions 8.0.40, 8.4.3, or 9.0.2 or later. If immediate patching is not feasible, restrict network access to MySQL ports using firewalls or network segmentation.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Mysql ServerDatabase / datastore
Affected:>= 8.0.0, <= 8.0.39>= 8.4.0, <= 8.4.2>= 9.0.0, <= 9.0.1

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify MySQL version
    Run SELECT VERSION(); or mysql --version from command line
    Affected if Version falls within 8.0.0-8.0.39, 8.4.0-8.4.2, or 9.0.0-9.0.1
  2. Check if thread pooling is enabled
    Run SHOW VARIABLES LIKE 'thread_pool%'; to see thread pool configuration
    Affected if Thread pooling is active (thread_pool_size is set to a non-default value or thread_pool_mode is enabled)
  3. Verify network exposure
    Check MySQL bind-address and port configuration via SHOW VARIABLES LIKE 'bind_address'; and confirm port 3306 is externally accessible
    Affected if MySQL port is reachable from untrusted networks (not localhost-only or firewalled)

You are affected if your MySQL version is in the vulnerable range AND thread pooling is enabled AND the database is network-accessible to unauthenticated attackers.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to a release after 9.0.1
Interim mitigation

Apply Oracle MySQL security patches to upgrade to versions 8.0.40, 8.4.3, or 9.0.2 or later. If immediate patching is not feasible, restrict network access to MySQL ports using firewalls or network segmentation.

Recommended fix High confidence

MySQL 8.0.40, 8.4.3, or 9.0.2 (depending on your major version branch)

  1. 1. Identify the current MySQL Server version using: `mysql --version` or `SELECT VERSION();`
  2. 2. Stop the MySQL Server service before upgrading
  3. 3. For Oracle MySQL: Download and install MySQL Server 8.0.40 or later, 8.4.3 or later, or 9.0.2 or later from the official Oracle MySQL download page
  4. 4. For MySQL packages via package manager (e.g., yum, apt): Update the package repository and upgrade using: `yum update mysql-server` or `apt-get update && apt-get install mysql-server`
  5. 5. Start the MySQL Server service after upgrade
  6. 6. Verify the upgrade was successful by checking the version: `SELECT VERSION();`
  7. 7. Review Oracle MySQL release notes for any post-upgrade requirements or migration steps
Caveat Oracle MySQL minor version upgrades typically have minimal breaking changes but always review the release notes for deprecation notices and migration requirements before upgrading

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Mysql Server Scoped from the published advisory
  • Consultation3.0 h
  • Implementation4.0 h
  • Testing6.0 h
  • Review / QA2.0 h
15.0 hours of engineering $2,580
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2025-21521 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data