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Actively exploited

CVE-2021-37973 Google Chromium Portals Use-After-Free Vulnerability

Google Chromium Portals contains a use-after-free vulnerability that allows a remote attacker, who has compromised the renderer process, to potentially perform a sandbox escape via a crafted HTML page. This vulnerability affects web browsers that utilize Chromium, including Google Chrome and Microsoft Edge.

From the CISA KEV catalogue version 2026.11.06, with Cybergen analysis. Updated 6 Nov 2026.

Our Assessment

Should You Worry?

Patch nowCybergen assessment
  • CISA confirmed exploitation in the wild and added it to the Known Exploited Vulnerabilities catalogue on 3 Nov 2021.
  • Rated Critical severity (CVSS 9.6, scored by CISA).
  • It has been in the catalogue for 1,829 days. Systems still unpatched now have almost certainly been scanned for it.
The Vulnerability

What It Is

Use after free in Portals in Google Chrome prior to 94.0.4606.61 allowed a remote attacker who had compromised the renderer process to potentially perform a sandbox escape via a crafted HTML page.

Affected Versions

ProductVersions
Google Chromeunspecified to before 94.0.4606.61

From the public CVE record, as supplied by the vendor. Always confirm against the vendor advisory.

From Watch to Action

What To Do Now

  1. 1

    Find it

    Search your asset inventory and external attack surface for Google Chromium Portals. Include cloud images, appliances and anything a supplier runs for you.

    Attack Surface Management
  2. 2

    Fix it

    Apply updates per vendor instructions.

    Vulnerability Management
  3. 3

    Hunt for compromise

    If an affected system was reachable before you patched, assume it may have been hit. Check logs, new accounts, web shells and outbound connections from the date of exposure.

    Incident Response
  4. 4

    Prove it is fixed

    Rescan or test the system after patching. Upgrades that fail silently and forgotten secondary instances are common.

    Penetration Testing

Vendor Advisories

Regulation

The Compliance Clock

Cyber EssentialsRated critical, so if it affects devices in your Cyber Essentials scope, the update must be installed within 14 days of the vendor releasing it.NIS2If exploitation causes a significant incident, essential and important entities owe their CSIRT an early warning within 24 hours and a notification within 72 hours.DORAFinancial entities must classify ICT incidents and send an initial notification for a major incident within strict deadlines, with exploited flaws a common cause.US federal (BOD 22-01)Federal civilian agencies had until 17 Nov 2021 to remediate. A sensible benchmark for everyone else.

General guidance, not legal advice. Your obligations depend on your sector, scope and jurisdiction.

Stay Ahead

More Exploited Google Flaws

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CVE-2026-111497Google Brotli Unchecked Return Value VulnerabilityAdded 27 Oct 2026CVE-2026-58704Google Pixel Improper Authorization VulnerabilityAdded 16 Sep 2026CVE-2026-87491Google Chromium V8 Out of Bounds Write VulnerabilityAdded 9 Sep 2026CVE-2026-85046Google Chromium V8 Type Confusion VulnerabilityAdded 4 Sep 2026CVE-2026-11645Google Chromium V8 Out-of-Bounds Read and Write VulnerabilityAdded 9 Jun 2026CVE-2026-5281Google Dawn Use-After-Free VulnerabilityAdded 1 Apr 2026

All 76 exploited Google vulnerabilities

Not Sure If You Are Exposed?

Our attack surface and vulnerability teams can check your internet-facing estate for CVE-2021-37973 and every other exploited flaw on the list.

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Evidence

Sources

  1. CISA Known Exploited Vulnerabilities catalogue
  2. NVD: CVE-2021-37973
  3. CVE record: CVE-2021-37973
  4. FIRST EPSS
  5. crbug.com/1251727
  6. chromereleases.googleblog.com/2021/09/stable-channel-update-for-desktop_24.html
  7. lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/4DDW7HAHTS3
  8. lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/PM7MOYYHJSW
  9. debian.org/security/2022/dsa-5046