Apple iOS WebKit Buffer Overflow Vulnerability

Are you affected?

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• cpe apple/iphone osversion unspecified
• vendor Apple iOSversion unspecified

How to fix CVE-2021-30666

• Recommended remediation

  Apply updates per vendor instructions. CISA due date Nov 17, 2021.

• Official advisories

  • CISA KEV · cisa.gov
  • CVE.org · cve.org
  • FIRST EPSS · first.org
  • NIST NVD · nvd.nist.gov
  • VulnCheck KEV · vulncheck.com

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Code

The project this record applies to. Exploit listings stay in References.

No public source repository is identified for this product.

Timeline

Detection, updates, and resolution for this record.

1. Sep 8, 2021 · Catalog

   Detected

   Apple iOS WebKit contains a buffer-overflow vulnerability that leads to code execution when processing maliciously crafted web content. 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.

2. Nov 3, 2021 · CISA KEV

   Known exploited

   Apply updates per vendor instructions.

3. Nov 17, 2021 · CISA KEV

   Remediation due

   Apply updates per vendor instructions.

4. Jun 16, 2026 · Catalog

   Updated

   Apple iOS WebKit contains a buffer-overflow vulnerability that leads to code execution when processing maliciously crafted web content. 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.

Sources

• CISA KEVConfirmed exploitationCVE-2021-30666

  Apple iOS WebKit contains a buffer-overflow vulnerability that leads to code execution when processing maliciously crafted web content. 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.

  cisa.gov
• CVE.orgVulnerability recordCVE-2021-30666

  Official CVE identifier

  cve.org
• FIRST EPSSExploitation probabilityCVE-2021-30666

  30-day exploitation probability 3.0%

  first.org
• NIST NVDVulnerability recordCVE-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..

  nvd.nist.gov
• VulnCheck KEVConfirmed exploitationCVE-2021-30666

  Apple iOS WebKit contains a buffer-overflow vulnerability that leads to code execution when processing maliciously crafted web content. This vulnerability could impact HTML parsers that use WebKit, including but not limited to Apple Safari and non-Apple products which rely on Web

  vulncheck.com

References

• CISA note · nvd.nist.gov
• Release Notes · support.apple.com
• VulnCheck exploitation evidence · support.apple.com
• Third Party Advisory · cisa.gov
• VulnCheck exploitation evidence · cisa.gov

Freshness

Last verified in this catalog Oct 17, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.