Threats / Google / CVE-2021-37973
CVE-2021-37973
· EUVD no mirror located
· GCVE no mirror located
Verified 2026-08-04
Google Chromium Portals vulnerability
Use-after-free vulnerability in Google Chromium Portals allows a compromised renderer process to escape the sandbox via crafted HTML, affecting Chrome and Edge browsers.
Verdict
Today item — known-exploited.
A remote attacker who has already compromised the renderer process can exploit this use-after-free to potentially escape the browser sandbox. Active exploitation in the wild has been observed.
CISA KEV Yes · 2021-11-034EPSS 0.11735 (verify live)5CVSS 9.6 (CISA)3CISA SSVC Exploitation: active · Automatable: no · Impact: total3
01
Is it exploitable?
— the evidence, ranked above the scoreReported exploitation
6 independent public reports of in-the-wild exploitation are cataloged.Distinct reporting sources (vendor, incident response, government); open them for the underlying claims.
Exploited in the wild
Listed in the CISA Known Exploited Vulnerabilities catalog (added 2021-11-03).
Probability (EPSS)
EPSS 0.11735 — modeled likelihood of exploitation activity.EPSS is a daily-changing model output — open the source for today's value.
Severity / affected
CVSS 9.6 (CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H) · Affected: Google, Chromium Portals. Confirm exact fixed builds in the vendor advisory.CVSS — CISA-assigned via the ADP container (CVE.org), version 3.1; the CNA left no metrics, so CISA's own score is used ahead of NVD.
Weakness (CWE)
Mapped to CWE-416 Use After Free — weakness family: Memory safety.CWE assignment from the public NVD record (may be stale); the weakness class drives how the flaw is exploited.
CISA SSVC (triage disposition)
Exploitation: active · Automatable: no · Technical Impact: totalCISA's own stakeholder-specific triage inputs, published in the CVE record (CISA Coordinator role). NOTE: this is CISA's three decision points; the final Act/Attend/Track decision also requires a Mission & Well-being input not published here, so no overall decision is asserted.
Currency of the record
CISA added this to its KEV catalog 26 days after the CVE record was published.KEV lag = CISA-KEV dateAdded − CVE.org datePublished; a floor on how long the known-exploited flaw sat in the public record before the federal catalog listed it. Severity/weakness here is CNA- or CISA-assigned (current at disclosure), independent of NVD's analysis backlog.
02
Who’s exploiting it?
— attribution turns risk into urgencyAttribution not established
No confirmed (advisory-backed) threat-actor attribution is established for this record. Absence of a named actor is not absence of compromise — see Coverage & confidence.
03
Why it matters
— the attack path, told twice: adversary, then board1
Front door — unauthenticated access narrative 1
Attacker
I craft malicious HTML that triggers a use-after-free condition in the Portals implementation.
Business
User visits attacker-controlled or compromised website, initiating the attack chain.
2
Keys to the kingdom — privilege/identity takeover narrative 2
Attacker
I exploit the use-after-free to gain code execution within the renderer process.
Business
Attacker gains ability to read sensitive data from the renderer and bypass same-origin policies.
3
Lateral reach — past segmentation narrative 3
Attacker
I leverage renderer code execution to escape the sandbox and access the host system.
Business
System compromise becomes possible, enabling malware installation, credential theft, or lateral movement.
04
What to do
— defensible action- Remediate per the vendor advisory — confirm the fixed build for your version and verify exposure.1
Say it to the boardA vulnerability with this evidence profile is a defensible budget line, not a backlog ticket — fund the change against the proof above.
05