How severe is CVE-2021-30666?

CVE-2021-30666 has a CVSS 3.x base score of 8.8, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2021-30666 being actively exploited?

Yes. CVE-2021-30666 is on CISA's Known Exploited Vulnerabilities (KEV) catalog, added on 2021-11-03, which means active exploitation has been confirmed. It should be prioritised for remediation.

What products are affected by CVE-2021-30666?

CVE-2021-30666 affects Apple Iphone Os. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-30666?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Because this CVE is known to be actively exploited, treat remediation as urgent — CISA KEV typically sets a short remediation deadline.

Does CVE-2021-30666 have an EU (EUVD) identifier?

Yes. CVE-2021-30666 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2021-17583. It is also flagged as exploited in the EUVD (since 2021-11-03).

When was CVE-2021-30666 published?

CVE-2021-30666 was published on 2021-09-08 and last updated on 2026-06-17.

CVE-2021-30666

CVE-2021-30666 is a high-severity vulnerability in Apple Iphone Os with a CVSS 3.x base score of 8.8. It is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog, confirming it has been exploited in the wild (added 2021-11-03). The underlying weakness is classified as CWE-119.

Key facts

Severity: High (CVSS 3.x base score 8.8)
CVSS v2: 6.8
EPSS exploit prediction: 3% (86th percentile)
Actively exploited: Yes — listed in CISA KEV (added 2021-11-03)
EU (EUVD) id: EUVD-2021-17583
EU exploitation: Flagged exploited in the ENISA EU Vulnerability Database (since 2021-11-03)
Weakness: CWE-119
Affected product: Apple Iphone Os
Published: 2021-09-08
Last modified: 2026-06-17

Description

A buffer overflow issue was addressed with improved memory handling. This issue is fixed in iOS 12.5.3. Processing maliciously crafted web content may lead to arbitrary code execution. Apple is aware of a report that this issue may have been actively exploited..

Frequently asked questions

What is CVE-2021-30666?: A buffer overflow issue was addressed with improved memory handling. This issue is fixed in iOS 12.5.3. Processing maliciously crafted web content may lead to arbitrary code execution. Apple is aware of a report that this issue may have been actively exploited..
How severe is CVE-2021-30666?: CVE-2021-30666 has a CVSS 3.x base score of 8.8, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2021-30666 being actively exploited?: Yes. CVE-2021-30666 is on CISA's Known Exploited Vulnerabilities (KEV) catalog, added on 2021-11-03, which means active exploitation has been confirmed. It should be prioritised for remediation.
What products are affected by CVE-2021-30666?: CVE-2021-30666 affects Apple Iphone Os. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-30666?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Because this CVE is known to be actively exploited, treat remediation as urgent — CISA KEV typically sets a short remediation deadline.
Does CVE-2021-30666 have an EU (EUVD) identifier?: Yes. CVE-2021-30666 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2021-17583. It is also flagged as exploited in the EUVD (since 2021-11-03).
When was CVE-2021-30666 published?: CVE-2021-30666 was published on 2021-09-08 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:o:apple:iphone_os:*:*:*:*:*:*:*:*

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