← Vulnerability feed

Vulnerability record · CVE-2021-30663 · published 8 September 2021

CVE-2021-30663: Apple WebKit integer overflow allows code execution

Apple · Safari

An integer overflow in Apple's WebKit engine was addressed with improved input validation. Processing maliciously crafted web content can lead to arbitrary code execution, affecting Safari, iOS, iPadOS, macOS and tvOS. The flaw is remotely reachable and listed in CISA's Known Exploited Vulnerabilities catalog, so it warrants prompt patching.

8.8 CVSS 3.1 High CISA KEV since 3 Nov 2021 EPSS 3.5% · top 11.3% CWE-190 · Integer overflow
8.8CVSS 3.1 base score, v2 6.8
3.5%EPSS exploitation probability, 30 days
YesIn CISA KEV, fix deadline passed
5Affected product versions listed by NVD
11References
17 Jun 2026Last modified by NVD

Description

An integer overflow was addressed with improved input validation. This issue is fixed in iOS 14.5.1 and iPadOS 14.5.1, tvOS 14.6, iOS 12.5.3, Safari 14.1.1, macOS Big Sur 11.3.1. Processing maliciously crafted web content may lead to arbitrary code execution.

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

Automated analysis

Generated by VULONE's analysis model from the NVD record, CISA KEV and EPSS data on 17 September 2026. Confidence: high.

high priorityRemote code execution in widely deployed Apple products with confirmed in-the-wild exploitation per CISA KEV, though user interaction is required.

What it is

An integer overflow in Apple's WebKit engine was addressed with improved input validation. Processing maliciously crafted web content can lead to arbitrary code execution, affecting Safari, iOS, iPadOS, macOS and tvOS. The flaw is remotely reachable and listed in CISA's Known Exploited Vulnerabilities catalog, so it warrants prompt patching.

Impact

An attacker can execute arbitrary code in the context of the affected browser or web content process, potentially gaining control of the device or user data. The CVSS vector rates high confidentiality, integrity and availability impact.

Attack surface

Reached over the network by serving malicious web content; no privileges are required but user interaction (visiting or rendering the crafted content) is needed per the CVSS vector. No authentication is required.

Exploitation

Listed in CISA KEV with a 2021-11-17 remediation due date, indicating known exploitation in the wild. EPSS 30-day probability is about 3.5 percent (88.5th percentile), and references are vendor advisories plus the KEV entry.

What to do

  • Apply the vendor updates: iOS 14.5.1 and iPadOS 14.5.1, tvOS 14.6, iOS 12.5.3, Safari 14.1.1, macOS Big Sur 11.3.1.
  • Prioritize patching internet-facing and user-facing Apple devices, especially those used for browsing.
  • Enforce automatic updates or a patch management process to confirm all listed products are on fixed versions.
  • Where patching is delayed, restrict browsing of untrusted web content and consider content filtering.
  • Track KEV remediation deadlines and verify closure for all affected assets.

Detection

  • Monitor for exploitation attempts against WebKit via browser or endpoint telemetry, focusing on crashes or anomalous code execution in Safari/WebKit processes.
  • Review device inventories for unpatched iOS, iPadOS, macOS, tvOS and Safari versions against the fixed releases.
  • Correlate web proxy or DNS logs for delivery of malicious web content to Apple devices.
  • Alert on unexpected process creation or memory corruption indicators originating from browser processes.

This assessment is produced automatically and is not human-reviewed. Verify against the vendor advisory before acting on it.

Exploitation in the wild

CISA added CVE-2021-30663 to the Known Exploited Vulnerabilities catalog on 3 November 2021 as "Apple Multiple Products WebKit Integer Overflow Vulnerability". Required action: Apply updates per vendor instructions. Federal deadline 17 November 2021.

Affected products

5 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://support.apple.com/en-us/HT212335 Release NotesVendor Advisory
https://support.apple.com/en-us/HT212336 Release NotesVendor Advisory
https://support.apple.com/en-us/HT212341 Release NotesVendor Advisory
https://support.apple.com/en-us/HT212532 Release NotesVendor Advisory
https://support.apple.com/en-us/HT212534 Release NotesVendor Advisory
https://support.apple.com/en-us/HT212335 Release NotesVendor Advisory
https://support.apple.com/en-us/HT212336 Release NotesVendor Advisory
https://support.apple.com/en-us/HT212341 Release NotesVendor Advisory
https://support.apple.com/en-us/HT212532 Release NotesVendor Advisory
https://support.apple.com/en-us/HT212534 Release NotesVendor Advisory
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-30663 Third Party AdvisoryUS Government Resource

Track CVE-2021-30663 inside VULONE

Watch it alongside the ransomware crews, C2 infrastructure and forum chatter that reference it, query it through the API and pull it into your SIEM over TAXII.

Start free Open in platform

Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

10.0CVE-2025-43300Apple iOS, iPadOS and macOS out-of-bounds write via malicious imageAn out-of-bounds write in Apple iOS, iPadOS and macOS is triggered when processing a malicious image file, causing memory corruption. Apple states th…KEVEPSS 22%analysed10.0CVE-2025-24201Apple WebKit out-of-bounds write allows sandbox escapeCVE-2025-24201 is an out-of-bounds write in Apple's WebKit that was addressed with improved checks. Maliciously crafted web content may break out of …KEVEPSS 3.8%analysed10.0CVE-2025-24085Apple iOS, iPadOS, macOS, tvOS, visionOS, watchOS Use-After-Free Privilege EscalationA use-after-free flaw in Apple's operating systems was fixed through improved memory management in iOS 18.3, iPadOS 18.3 and 17.7.6, macOS Sequoia 15…KEVEPSS 18%analysed9.8CVE-2026-65400Apple macOS Screen Sharing authentication bypassAn improper authentication flaw in Apple macOS Screen Sharing allows a network attacker to authenticate without valid credentials. Apple fixed it via…KEVEPSS 1.2%analysed9.8CVE-2025-31200Apple OS media parsing memory corruption allows code executionA memory corruption flaw in Apple's audio stream processing was fixed with improved bounds checking across iOS, iPadOS, macOS, tvOS, visionOS and wat…KEVEPSS 19%analysed9.8CVE-2025-31201Apple OS Pointer Authentication bypass via arbitrary read/writeApple removed vulnerable code that allowed an attacker holding arbitrary read and write capability to bypass Pointer Authentication across iOS, iPadO…KEVEPSS 14%analysed9.8CVE-2022-22587Apple iOS, iPadOS and macOS kernel memory corruption via out-of-bounds writeAn out-of-bounds write (CWE-787) in Apple iOS, iPadOS and macOS is caused by insufficient input validation and can corrupt memory. Apple states it is…KEVEPSS 12%analysed9.8CVE-2021-1870Apple WebKit logic flaw allows remote code executionA logic issue in Apple's WebKit was addressed with improved restrictions, affecting macOS Big Sur, Catalina, Mojave, iOS and iPadOS, plus WebKitGTK a…KEVEPSS 7.7%analysed

Source: NIST National Vulnerability Database (record CVE-2021-30663), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.