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Actively exploited in the wild. This CVE is on the CISA Known Exploited Vulnerabilities list — treat remediation as urgent. Federal remediation due by 17 Nov 2021.
SafariWeb browser · Apple

CVE-2021-30663

HIGH · 8.8 CVSS v3.1 Published 2021-09-08
Fix available
A fix is available. Upgrade to 11.3.1 / 12.5.3 or later.
See remediation →
100/100
Remediation priority · Urgent
In the wild 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
An integer overflow was addressed with improved input validation. This issue is fixed in iOS 14.5.1 and iPadOS 14.5.1, tvOS 14.6, iOS 12.5.3, Safari 14.1.1, macOS Big Sur 11.3.1. 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

Integer overflow vulnerability in WebKit allowing arbitrary code execution when processing maliciously crafted web content, fixed through improved input validation.

MitigationApply vendor patches: update to iOS 14.5.1+/iPadOS 14.5.1+/tvOS 14.6+/iOS 12.5.3+/Safari 14.1.1+/macOS Big Sur 11.3.1+ on all affected devices.

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
SafariWeb browser
Affected:< 14.1.1
IpadosOperating system
Affected:>= 14.0, < 14.5.1
Iphone OsOperating system
Affected:< 12.5.3>= 14.0, < 14.5.1
macOSOperating system
Affected:>= 11.0, < 11.3.1
TvosOperating system
Affected:< 14.6

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 your Apple device and operating system
    On iPhone/iPad: go to Settings > General > About to see iOS/iPadOS version. On Mac: click Apple menu > About This Mac to see macOS version. On Apple TV: go to Settings > General > About to see tvOS version.
    Affected if The device runs any of the affected Apple operating systems (iOS, iPadOS, macOS, tvOS) or uses Safari browser.
  2. Check the installed Safari version on macOS
    Open Safari, then click Safari menu > About Safari to view the version number.
    Affected if Safari version is earlier than 14.1.1 on macOS.
  3. Check iOS or iPadOS version
    Go to Settings > General > About on iPhone or iPad and note the version number.
    Affected if iOS/iPadOS version is earlier than 12.5.3, or is 14.0 to 14.5.1 range.
  4. Check tvOS version on Apple TV
    Go to Settings > General > About on Apple TV and note the version number.
    Affected if tvOS version is earlier than 14.6.
  5. Confirm WebKit usage
    This vulnerability affects WebKit, the rendering engine used by Safari and in-app browsers on Apple devices. If you use Safari or any app that renders web content, WebKit is active.
    Affected if You use Safari or any application that utilizes WebKit for web content rendering on an affected device.

You are affected if your device runs an Apple operating system or Safari version that falls within the vulnerable ranges: iOS/iPadOS < 12.5.3 or 14.0-14.5.1, macOS 11.0-11.3.1 with Safari < 14.1.1, tvOS < 14.6, or Safari < 14.1.1 on older macOS versions.

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 11.3.1 / 12.5.3 / 14.1.1 or later
Fixed in 11.3.112.5.314.1.1
Interim mitigation

Apply vendor patches: update to iOS 14.5.1+/iPadOS 14.5.1+/tvOS 14.6+/iOS 12.5.3+/Safari 14.1.1+/macOS Big Sur 11.3.1+ on all affected devices.

Recommended fix High confidence

Upgrade to iOS 14.5.1 / iOS 12.5.3, iPadOS 14.5.1, macOS Big Sur 11.3.1, tvOS 14.6, or Safari 14.1.1 as appropriate for your device

  1. For iPhone and iPod Touch: Go to Settings > General > Software Update and install iOS 14.5.1 (or iOS 12.5.3 for devices that cannot run iOS 14)
  2. For iPad: Go to Settings > General > Software Update and install iPadOS 14.5.1
  3. For Mac: Go to System Preferences > Software Update and install macOS Big Sur 11.3.1
  4. For Apple TV: Go to Settings > General > Software Update and install tvOS 14.6
  5. For Safari on older macOS: Download and install Safari 14.1.1 from Apple's support website
Caveat Standard OS upgrade considerations apply - ensure backup of important data before upgrading

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

Fix this in Safari Exploited in the wild — priority engagement
  • Consultation3.0 h
  • Implementation6.0 h
  • Testing3.0 h
  • Review / QA2.0 h
14.0 hours of engineering $2,490
Get it fixed fast

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,984.

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-2021-30663 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