What is CVE-2021-1871?

CVE-2021-1871 is a critical-severity vulnerability in Apple iOS And Ipados. CVSS score: 9.8/10. Published 2021-04-02.

How severe is CVE-2021-1871?

Critical severity. CVSS v3 base score is 9.8 out of 10.

Is CVE-2021-1871 known to be exploited?

Yes. CVE-2021-1871 is listed in the CISA Known Exploited Vulnerabilities catalog (added 2021-11-03), indicating it is being actively exploited. 5 public proof-of-concept repositories are indexed.

Vulnerability in Apple iOS And Ipados

CVE-2021-1871

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..

Published 2021-04-02 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.070 (94.1th percentile), scored 2026-10-20.

Low probability of exploitation in the next 30 days, but still tracked. 94th percentile — 94.1% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.070 · newest: 0.070 · change: 0.000

Affected products

Apple iOS And Ipados — versions unspecified
Apple Ipados
Apple Iphone OS
Apple macOS — versions unspecified
Apple Mac OS X — versions 10.15.7
Debian Linux — versions 10.0
Fedoraproject Fedora — versions 33

CISA KEV (Known Exploited Vulnerabilities)

This CVE is on the CISA KEV catalog, added on 2021-11-03. CISA KEV inclusion means CISA has confirmed in-the-wild exploitation; US federal agencies are required to remediate within a published due date.

BOD 22-01 due date: 2021-11-17.

Required action: Apply updates per vendor instructions.

Public proof-of-concept exploits

References

support.apple.com/en-us/HT212147 (Release Notes, Vendor Advisory)
support.apple.com/en-us/HT212146 (Release Notes, Vendor Advisory)
lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/… (vendor-advisory, Mailing List, Broken Link)
www.debian.org/security/2021/dsa-4923 (vendor-advisory, Mailing List, Third Party Advisory)
134c704f-9b21-4f2e-91b3-4a467353bcc0 (US Government Resource)

Frequently asked questions

What is CVE-2021-1871?: CVE-2021-1871 is a critical-severity vulnerability in Apple iOS And Ipados. CVSS score: 9.8/10. Published 2021-04-02.
How severe is CVE-2021-1871?: Critical severity. CVSS v3 base score is 9.8 out of 10.
Is CVE-2021-1871 known to be exploited?: Yes. CVE-2021-1871 is listed in the CISA Known Exploited Vulnerabilities catalog (added 2021-11-03), indicating it is being actively exploited. 5 public proof-of-concept repositories are indexed.