CVE-2021-30663Known exploitationNetwork attack vector

Code execution via WebKit integer overflow

Published Sep 8, 2021 · Updated Oct 21, 2025

Integer overflow in WebKit in Apple macOS Big Sur before 11.3.1 allows remote attackers to execute code through crafted web content. Apple has not disclosed the affected WebKit function; the published mechanism is insufficient input validation that permits an integer calculation to overflow. A user must load the content before attacker-supplied code can run with the process's privileges.

CVSS severity8.8
High
EPSS probability3.49%
Next 30 days · Sep 16, 2026
Known exploitationReported
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Integer overflow in WebKit in Apple macOS Big Sur before 11.3.1 allows remote attackers to execute code through crafted web content. Apple has not disclosed the affected WebKit function; the published mechanism is insufficient input validation that permits an integer calculation to overflow. A user must load the content before attacker-supplied code can run with the process's privileges.

The record

CVE
CVE-2021-30663
Published
Sep 8, 2021
Updated
Oct 21, 2025
Vendor
Apple
Product
macOS
Classifications
CWE-190, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 8, 2021CVE publishedPublication date reported by the CVE source.
  2. Nov 3, 2021Exploitation reportedCISA Known Exploited Vulnerabilities listing
  3. Oct 21, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=unspecified <11.3
  2. Affected versionversion=unspecified <12.5
  3. Affected versionversion=unspecified <14.1
  4. Affected versionversion=unspecified <14.5
  5. Affected versionversion=unspecified <14.6

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Apple · macOSversion=unspecified <11.3; version=unspecified <12.5; version=unspecified <14.1; version=unspecified <14.5; version=unspecified <14.6

Published CVSS scores

8.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
7.8CISA-ADPCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
6.8NIST NVDAV:N/AC:M/Au:N/C:P/I:P/A:P

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationReported
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-190Integer Overflow or Wraparound
T1203Exploitation for Client Execution

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Reported exploitation

Technologies

Your stack

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Your stack

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