IRONSMITHINTEL
CRITICALCVSS9.8
|
Actively Exploited
|CISA KEV|CVE-2021-1871|Auth: none — unauthenticated|Reboot: required|Manual only

Apple iOS, iPadOS, and macOS WebKit Remote Code Execution Vulnerability (CVE-2021-1871)

Apple iOS, iPadOS, and macOS WebKit contain an unspecified logic vulnerability that allows a remote attacker to execute code. This vulnerability could impact HTML parsers that use WebKit, including but not limited to Apple Safari and non-Apple products which rely on WebKit for HTML processing.

Published Apr 2, 2021 · Updated May 17, 2026
Why patchRisk explained in plain English
Worst-case scenarioIf unpatched

A remote attacker, without authentication, can achieve full data confidentiality loss, arbitrary modification of data, complete denial of service or system unavailability. Federal agencies are required to remediate by 2021-11-17 under CISA BOD 22-01.

How the attack worksNo clicks needed

This vulnerability affects Apple iOS, iPadOS, and macOS. A logic issue was addressed with improved restrictions. This issue is fixed in macOS Big Sur 11.2, Security Update 2021-001 Catalina, Security Update 2021-001 Mojave, iOS 14.4 and iPadOS 14.4. A remote attacker may be able to cause arbitrary code execution. Apple is aware of a report that this issue may have been actively exploited.. Exploitation requires remote network access, low attack complexity, no authentication required, and no user interaction required.

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Phishing link

→

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Malicious file

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Server compromised

Am I affected?Quick check

Probably yes if any of these apply:

●Apple Device Administrators
●Endpoint Security
●IT Security
●Running ipados: v < 14.4; iphone os: v < 14.4; mac os x: 10.15 ≤ v < 10.15.7, 10.15.7; macos: 11.0.1 ≤ v < 11.2; debian linux: 10.0; fedora: 33
Real-world incidentsWhat we've seen

CISA added this CVE to the Known Exploited Vulnerabilities catalog on 2021-11-03 based on evidence of active exploitation in the wild. Federal agencies required to remediate by 2021-11-17.

How to patch

Manual remediation steps

1
Identify affected hosts: query inventory for os installs in scope.
2
Apply the vendor security update referenced in CVE-2021-1871's advisory. No specific KB/version is encoded yet — consult the linked MSRC/vendor URL.
3
Verify the fix per the vendor's published verification steps.
4
Document the remediation in your change ticket and re-scan with your vulnerability scanner to confirm closure.
PowerShell automationComing soon

No tested PowerShell script for this entry yet. We’re prioritising automation based on user demand.

References

↗ CVE-2021-1871↗ MSRC Advisory↗ NVD↗ Vendor Advisory