Cyber Resilience

CVE-2021-30663

Memory Safety in Apple Iphone Os ≤ 12.5.3

CISA KEVActive ExploitationEUVD ExploitedMemory Safety
Published
08 September 2021
Modified
23 October 2025
KEV Added
03 November 2021
Patch / advisory
View advisory
CVSS Score v3.1 8.8
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
EPSS Score 0.037 89th percentile
Risk Priority 90 floored blend · peak EPSS

Summary

CVE-2021-30663 is a high-severity Integer Overflow or Wraparound (CWE-190) vulnerability in Apple Iphone Os. Its CVSS base score is 8.8 (High).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Privilege Escalation (T1068); ranked in the top 11% of CVEs by exploit likelihood; CISA has added it to the Known Exploited Vulnerabilities catalog.

Deeper analysis AI-assisted summary

Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.

An integer overflow vulnerability, tracked as CVE-2021-30663 and assigned CWE-190, was present in the web content processing components of multiple Apple platforms. It affected iOS prior to 14.5.1 and 12.5.3, iPadOS prior to 14.5.1, tvOS prior to 14.6, Safari prior to 14.1.1, and macOS Big Sur prior to 11.3.1. The flaw was resolved through improved input validation in those releases.

A remote attacker can trigger the issue by supplying maliciously crafted web content that a user is induced to process, such as via a web browser or other WebKit-based application. Successful exploitation yields arbitrary code execution with high impact on confidentiality, integrity, and availability, consistent with the CVSS 3.1 vector AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H.

Apple security advisories for the listed updates direct administrators and users to install the patched versions of iOS, iPadOS, tvOS, Safari, and macOS Big Sur to address the integer overflow. No further details on exploitation in the wild are provided in the references.

EU & UK References

Vulnerability Data

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.

CWE(s)
CWE-190
KEV Date Added
03 November 2021

Related Threats

MITRE ATT&CK Enterprise Techniques

T1068 Exploitation for Privilege Escalation Privilege Escalation
Adversaries may exploit software vulnerabilities in an attempt to elevate privileges.
attack.mitre.org →
T1190 Exploit Public-Facing Application Initial Access
Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.
attack.mitre.org →
T1203 Exploitation for Client Execution Execution
Adversaries may exploit software vulnerabilities in client applications to execute code.
attack.mitre.org →
T1210 Exploitation of Remote Services Lateral Movement
Adversaries may exploit remote services to gain unauthorized access to internal systems once inside of a network.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2023-32434Same product: Apple Ipadosboth on KEV
CVE-2022-42856Same product: Apple Ipadosboth on KEV
CVE-2024-23222Same product: Apple Ipadosboth on KEV
CVE-2021-30661Same product: Apple Ipadosboth on KEV
CVE-2023-28205Same product: Apple Ipadosboth on KEV
CVE-2023-43000Same product: Apple Ipadosboth on KEV
CVE-2022-22620Same product: Apple Ipadosboth on KEV
CVE-2023-23529Same product: Apple Ipadosboth on KEV
CVE-2022-48503Same product: Apple Ipadosboth on KEV
CVE-2023-27937Same product: Apple Ipados

Affected Assets

apple
safari
≤ 14.1.1
apple
ipados
14.0 — 14.5.1
apple
iphone os
≤ 12.5.3 · 14.0 — 14.5.1
apple
macos
11.0 — 11.3.1
apple
tvos
≤ 14.6

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)

—

Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)

—

Validate
Prove the fix (OWASP ASVS)
  • V5.2.6

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.PS-06 mostly match
prevents

Secure SDLC practices directly require use of safe arithmetic, bounds checks, and testing that prevent integer overflows.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.8.29 Security testing in development and acceptance mostly match
finds

Security testing in development can detect integer overflows before release.

A.8.25 Secure development life cycle partial match
prevents

Secure SDLC mandates input validation and arithmetic checks that prevent integer overflows.

A.8.26 Application security requirements partial match
degrades

Application security requirements include bounds checking and safe arithmetic to avoid overflow conditions.

A.8.27 Secure system architecture and engineering principles partial match
degrades

Secure architecture principles require defensive coding patterns that mitigate integer wraparound risks.

A.8.28 Secure coding partial match
prevents

Secure coding standards explicitly forbid unsafe integer operations and mandate overflow-safe constructs.

References