CVE-2021-1871: Apple iOS, iPadOS, and macOS WebKit Remote Code Execution Vulnerability
- Is it exploited?
Yes. CISA added it to the Known Exploited Vulnerabilities catalog on 3 Nov 2021, 215 days after the CVE record was published.
- How likely is exploitation in the next 30 days?
- 7%
EPSS score, percentile 94.1 of all scored records
- How severe?
- 9.8 Critical
CVSS v3.1 base score, from CISA's enrichment of the record
- What should I do?
Required action (CISA), due 17 Nov 2021: Apply updates per vendor instructions.
- Which versions are affected?
Affected: before 14.4; before 11.2
Source: CISA Known Exploited Vulnerabilities (KEV) catalog, 2026.10.28, as of 28 Oct 2026; FIRST Exploit Prediction Scoring System (EPSS), v2026.06.15, as of 28 Oct 2026; CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.
What to do
Required action, set by CISA
Apply updates per vendor instructions.
CISA due date for this action: 17 November 2021.
Advisories and patches
Linked from CISA's catalog entry
Affected products and versions
As listed in the CVE record.
| Status | Versions |
|---|---|
| Affected | before 14.4 |
| Status | Versions |
|---|---|
| Affected | before 11.2 |
Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.
About this vulnerability
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.
Summary: CISA's KEV catalog, as of 28 Oct 2026.
- CISA added CVE-2021-1871 to its Known Exploited Vulnerabilities (KEV) catalog on 3 Nov 2021.
- CISA's ransomware flag for this entry is "Unknown": no evidence of ransomware use in the catalog, which is not proof of none.
- The due date CISA sets for the required action is 17 Nov 2021.
- The CVE record was published on 2 Apr 2021, 215 days before it was added to KEV.
- The CVE record carries a CVSS v3.1 base score of 9.8 (Critical), taken from CISA's enrichment of the record.
- FIRST's EPSS model puts the probability of exploitation in the next 30 days at 7% (percentile 94.1), as of 28 Oct 2026.
- CISA's SSVC assessment in the CVE record: exploitation active, automatable yes, technical impact total.
Source: CISA Known Exploited Vulnerabilities (KEV) catalog, 2026.10.28, as of 28 Oct 2026; CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026; FIRST Exploit Prediction Scoring System (EPSS), v2026.06.15, as of 28 Oct 2026. About the data.
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..
Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.
Weakness
CWE and CAPEC are maintained by MITRE; the entries are those named in the CVE record and the KEV entry.
Timeline
| Date | Event |
|---|---|
| 2 Apr 2021 | CVE record published |
| 3 Nov 2021 | Added to CISA KEV |
| 17 Nov 2021 | CISA due date for the required action |
| 21 Oct 2025 | CVE record last updated |
References
More exploited Apple vulnerabilities
- CVE-2026-86950: Apple Multiple Products Out-of-Bounds Write Vulnerability
- CVE-2026-65400: Apple macOS Improper Authentication Vulnerability
- CVE-2025-31277: Apple Multiple Products Buffer Overflow Vulnerability
- CVE-2025-43510: Apple Multiple Products Improper Locking Vulnerability
- CVE-2025-43520: Apple Multiple Products Classic Buffer Overflow Vulnerability
- CVE-2021-30952: Apple Multiple Products Integer Overflow or Wraparound Vulnerability