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CVE-2021-1871

Apple iOS, iPadOS, and macOS WebKit Remote Code Execution

9.8 CRITICALActively exploited (CISA KEV)EPSS 7.00%
  1. Published2 Apr 2021
  2. Added to CISA KEV3 Nov 2021
  3. Remediation due17 Nov 2021
Actively exploited (CISA KEV)

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.

Added to KEV: 3 Nov 2021Federal remediation due: 17 Nov 2021

Description

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..

CVSS 3.1 breakdown

Attack vectorNetwork
Attack complexityLow
Privileges requiredNone
User interactionNone
ScopeUnchanged
ConfidentialityHigh
IntegrityHigh
AvailabilityHigh
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected products

Apple iPadOS< 14.4
Apple iPhone OS< 14.4
Apple macOS≥ 11.0.1 < 11.2
Apple Mac OS X≥ 10.15 < 10.15.7 · 10.15.7
Debian Linux10.0
Fedoraproject Fedora33

Remediation

Fixed in
Apple iPadOS≥ 14.4
Apple iPhone OS≥ 14.4
Apple macOS≥ 11.2
Apple Mac OS X≥ 10.15.7

References

Frequently asked

Is CVE-2021-1871 being actively exploited?

Yes. CVE-2021-1871 is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, added 3 Nov 2021.

How severe is CVE-2021-1871?

CVE-2021-1871 has a CVSS 3.1 base score of 9.8, rated critical. EPSS estimates a 7.00% probability of exploitation.

Which products are affected by CVE-2021-1871?

Affected products include Apple iPadOS, Apple iPhone OS, Apple macOS, Apple Mac OS X, Debian Linux, and 1 more.

How do I fix CVE-2021-1871?

Upgrade affected software to a fixed version, for example Apple iPadOS 14.4, Apple iPhone OS 14.4, Apple macOS 11.2 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2021-1871 against the real software inventory on every managed device, as each hourly inventory arrives. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. Because it is on the CISA KEV list, a risk for it never ranks below high, and the update that fixes it moves to the Emergency patch lane. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.