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SafariWeb browser · Apple

CVE-2021-30851

HIGH · 8.8 CVSS v3.1 Published 2021-08-24
Fix available
A fix is available. Upgrade to 8.0 / 12.0.1 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 memory corruption vulnerability was addressed with improved locking. This issue is fixed in Safari 15, tvOS 15, watchOS 8, iOS 15 and iPadOS 15. Processing maliciously crafted web content may lead to 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 · moderate confidence

A memory corruption vulnerability in WebKit (Apple's browser engine) was addressed with improved locking, likely fixing a race condition. Processing maliciously crafted web content in affected Safari, iOS, iPadOS, watchOS, or tvOS versions could lead to arbitrary code execution.

MitigationApply the vendor-supplied updates: upgrade to Safari 15+, iOS 15+, iPadOS 15+, watchOS 8+, or tvOS 15+ to remediate this vulnerability.

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:< 15.0
Debian LinuxOperating system
Affected:= 10.0= 11.0
FedoraOperating system
Affected:= 33= 34
IpadosOperating system
Affected:< 15.0
Iphone OsOperating system
Affected:< 15.0
macOSOperating system
Affected:< 12.0.1= 12.0.1
TvosOperating system
Affected:< 15.0
WatchosOperating system
Affected:< 8.0

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. Check Safari version on macOS
    Open Safari, click Safari menu > About Safari. The version number appears next to the Safari logo.
    Affected if The version shown is less than 15.0 (for example 14.1.2) or exactly 15.0 shows as the initial release without subsequent updates.
  2. Check iOS version on iPhone or iPad
    Go to Settings > General > About. Look at the Version field.
    Affected if The version shown is less than 15.0 (for example 14.7.1).
  3. Check macOS version
    Click Apple menu > About This Mac. The version number appears below the macOS name.
    Affected if The macOS version is 12.0.1 or earlier than 12.0.1 (for example 12.0, 11.x).
  4. Check tvOS or watchOS version on Apple TV or Apple Watch
    On Apple TV: go to Settings > General > About > Version. On Apple Watch: open the Watch app on iPhone > General > About > watchOS Version.
    Affected if The tvOS version is less than 15.0 or the watchOS version is less than 8.0.
  5. Check WebKitGTK version on Debian or Fedora Linux
    For Debian: run `dpkg -l | grep webkit`. For Fedora: run `rpm -qa | grep webkit`. Compare the installed version number against the vulnerable releases.
    Affected if The installed webkit2gtk package version corresponds to the WebKit engine bundled in Safari versions before 15.0.

You are affected if you are running any Safari, iOS, iPadOS, macOS, tvOS, or watchOS version listed as vulnerable (below 15.0 for mobile OS, below 12.0.1 for macOS, or specific older versions on Linux distributions).

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 8.0 / 12.0.1 / 15.0 or later
Fixed in 8.012.0.115.0
Interim mitigation

Apply the vendor-supplied updates: upgrade to Safari 15+, iOS 15+, iPadOS 15+, watchOS 8+, or tvOS 15+ to remediate this vulnerability.

Recommended fix High confidence

Apple products: iOS 15 / iPadOS 15 / macOS 12.0.1 / tvOS 15 / watchOS 8 / Safari 15 or later; Linux: Contact vendor for patch availability

  1. For Apple devices (iOS, iPadOS, macOS, tvOS, watchOS, Safari): Update to the fixed version as indicated: iOS 15 and iPadOS 15 or later, macOS 12.0.1 or later, tvOS 15 or later, watchOS 8 or later, Safari 15 or later
  2. On iOS/iPadOS: Go to Settings > General > Software Update and install the latest available update
  3. On macOS: Go to System Preferences > Software Update or use the App Store to install macOS 12.0.1 or later
  4. On tvOS: Go to Settings > System > Software Updates and enable 'Update Automatically' to receive tvOS 15 or later
  5. On watchOS: On your iPhone, open the Watch app, go to My Watch > General > Software Update and install watchOS 8 or later
  6. For Safari: Update via macOS software update to receive Safari 15 or later, or download from apple.com/safari
  7. For Linux (Debian 10/11, Fedora 33/34): Check distribution security advisories for available patches or consider upgrading to a newer stable release
Caveat Standard OS update risks apply (ensure backups before updating, some legacy software may be incompatible with new OS versions)

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

Fix this in Safari Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing2.0 h
  • Review / QA2.0 h
10.0 hours of engineering $1,780
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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-2021-30851 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