dbcve.org
Mac Os XOperating system · Apple

CVE-2021-30766

HIGH · 7.8 CVSS v3.1 Published 2021-09-08
Fix available
A fix is available. Upgrade to 11.5 or later.
See remediation →
81/100
Remediation priority · High
No privileges

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
An out-of-bounds write was addressed with improved input validation. This issue is fixed in macOS Big Sur 11.5, Security Update 2021-004 Catalina, Security Update 2021-005 Mojave. An application may be able to execute arbitrary code with kernel privileges.

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

CVE-2021-30766 is a kernel-level out-of-bounds write vulnerability in macOS that allows a local attacker to execute arbitrary code with kernel privileges. The issue was addressed through improved input validation in vendor-supplied patches for macOS Big Sur 11.5 and Security Updates for Catalina and Mojave.

MitigationApply the appropriate Apple security update (macOS Big Sur 11.5, Security Update 2021-004 Catalina, or Security Update 2021-005 Mojave) to affected systems. This is a local privilege escalation vulnerability requiring an attacker to have local access to the target system.

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
Mac Os XOperating system
Affected:>= 10.14, <= 10.14.5>= 10.15, <= 10.15.6= 10.14.6= 10.15.7
macOSOperating system
Affected:>= 11.0, < 11.5

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
Local
Complexity
Low
Privileges
None
User interaction
Required
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/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. Check installed macOS version
    Run 'sw_vers -productVersion' in Terminal to get the exact version number (e.g., 10.15.7, 11.4)
    Affected if Version is 10.14.x where x <= 5, or 10.14.6, or 10.15.x where x <= 6, or 10.15.7, or 11.0.x where x < 5 (versions below 10.14.6, 10.15.7, or 11.5)
  2. Verify Security Update status
    Check System Preferences > Security & Privacy > General for recent security updates, or run 'defaults read /Library/Preferences/com.apple.SoftwareUpdate.plist LastSuccessfulDate'
    Affected if No security update installed in 2021 (specifically missing Security Update 2021-004 for Catalina or Security Update 2021-005 for Mojave)
  3. Confirm kernel extension loading (optional context)
    Run 'kextstat | grep -i apple' to list loaded Apple kernel extensions - this vulnerability is in low-level IOKit
    Affected if System is running unpatched macOS (the vulnerability exists regardless of specific configurations since it's a kernel input validation flaw)

The system is affected if it runs macOS 10.14.6, 10.15.7, or any macOS 11.0-11.4 (Big Sur) without the corresponding security patches applied.

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 11.5 or later
Fixed in 11.5
Interim mitigation

Apply the appropriate Apple security update (macOS Big Sur 11.5, Security Update 2021-004 Catalina, or Security Update 2021-005 Mojave) to affected systems. This is a local privilege escalation vulnerability requiring an attacker to have local access to the target system.

Recommended fix High confidence

macOS Big Sur 11.5 (or later), or apply Security Update 2021-004 (Catalina) / Security Update 2021-005 (Mojave)

  1. Check the current macOS version by clicking the Apple menu and selecting About This Mac
  2. For macOS Big Sur 11.0-11.4: Go to System Preferences > Software Update to install macOS Big Sur 11.5 or later
  3. For macOS Catalina (10.15): Go to System Preferences > Software Update to install Security Update 2021-004
  4. For macOS Mojave (10.14): Go to System Preferences > Software Update to install Security Update 2021-005
  5. After updating, restart the Mac to ensure the kernel security update takes effect
Caveat Standard upgrade considerations apply - ensure critical applications are compatible with the target OS version before updating

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

Fix this in Mac Os X Scoped from the published advisory
  • Consultation2.0 h
  • Implementation8.0 h
  • Testing4.0 h
  • Review / QA2.0 h
16.0 hours of engineering $2,800
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Scan for this in your stack

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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-2021-30766 in production — separate from our analysis above.

No notes yet

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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