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Known exploited · Apple

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

What it is

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 November 3, 2021Due November 17, 2021CISA KEV catalog 2026.10.01

Vendor
Apple
Product
iOS, iPadOS, and macOS
Added to KEV
November 3, 2021
CISA due date
November 17, 2021
Ransomware use
Unknown

What CISA requires

Apply updates per vendor instructions.

Forensic triage

No

What to do now

  1. Find every instance of iOS, iPadOS, and macOS you run, including the forgotten ones, and check its version against the vendor advisory.
  2. Apply the vendor's fix or mitigation, before November 17, 2021 if you are bound by CISA's deadline, sooner if it faces the internet.
  3. Assume it was tried against you already: look for signs of exploitation from the date it was added, not from the day you patched.

References

CVE-2021-1871 in the National Vulnerability Database

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Source: CISA Known Exploited Vulnerabilities Catalog (public domain), catalog version 2026.10.01.