dbcve.org
Mac Os XOperating system · Apple

CVE-2021-1876

HIGH · 8.8 CVSS v3.1 Published 2021-09-08
Fix available
A fix is available. Upgrade to 11.3 or later.
See remediation →
95/100
Remediation priority · Urgent
Remotely reachable 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
A use after free issue was addressed with improved memory management. This issue is fixed in macOS Big Sur 11.3, Security Update 2021-002 Catalina, Security Update 2021-003 Mojave. Processing maliciously crafted web content may lead to arbitrary code execution.

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

A use-after-free vulnerability in macOS web content processing (likely WebKit) allows arbitrary code execution when processing maliciously crafted web content. The vulnerability stems from improper memory management during web content handling.

MitigationApply the appropriate macOS security update: macOS Big Sur 11.3, Security Update 2021-002 for Catalina, or Security Update 2021-003 for Mojave. Until patched, avoid untrusted websites and disable JavaScript in browsers if possible.

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, <= 10.15.5= 10.14.6= 10.15.6= 10.15.7
macOSOperating system
Affected:>= 11.0, < 11.3

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
Required
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/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. Identify macOS version
    Run 'sw_vers -productVersion' in Terminal or check System Preferences > About
    Affected if Version is 10.14.x (10.14 to 10.14.6), 10.15.x (10.15 to 10.15.7), or 11.0 to 11.2.x (any version below 11.3)
  2. Confirm WebKit-based browser usage
    Identify browsers installed that use WebKit engine, such as Safari or any third-party browser relying on system WebKit
    Affected if WebKit-based browser (especially Safari) is installed and used
  3. Verify JavaScript is enabled
    In Safari: Preferences > Security > Enable JavaScript. In other WebKit browsers: check respective settings.
    Affected if JavaScript is enabled in the browser (required for web content to trigger the vulnerability)
  4. Check for recent security updates
    Run 'system_profiler SPSoftwareDataType' to view installed updates, or check System Preferences > Software Update for installed security patches
    Affected if No security update installed for this CVE (macOS 11.3, Security Update 2021-002 for Catalina, or Security Update 2021-003 for Mojave)

You are affected if your macOS version falls within 10.14-10.14.6, 10.15-10.15.7, or 11.0-11.2.x AND you use a WebKit-based browser with JavaScript enabled AND the corresponding security update is not installed.

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 11.3 or later
Fixed in 11.3
Interim mitigation

Apply the appropriate macOS security update: macOS Big Sur 11.3, Security Update 2021-002 for Catalina, or Security Update 2021-003 for Mojave. Until patched, avoid untrusted websites and disable JavaScript in browsers if possible.

Recommended fix High confidence

macOS Big Sur 11.3 or later (or Security Update 2021-002 for Catalina / Security Update 2021-003 for Mojave)

  1. For macOS Big Sur (11.x) users: Upgrade to macOS Big Sur 11.3 or later via System Preferences > Software Update
  2. For macOS Catalina (10.15) users: Apply Security Update 2021-002 through System Preferences > Software Update
  3. For macOS Mojave (10.14) users: Apply Security Update 2021-003 through System Preferences > Software Update
Caveat Security updates typically have minimal compatibility impact; however, ensure critical applications are compatible 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
  • Implementation4.0 h
  • Testing2.0 h
  • Review / QA1.0 h
9.0 hours of engineering $1,600
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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-2021-1876 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