Threats / Google / CVE-2021-30633

CVE-2021-30633 · EUVD no mirror located · GCVE no mirror located Verified 2026-09-19

Google Chromium Indexed DB API vulnerability

Use-after-free in Chromium Indexed DB API allows sandbox escape when renderer process is compromised via crafted HTML.

Verdict

Today item — known-exploited.

A use-after-free vulnerability in the Indexed DB API enables attackers with renderer process control to escape the sandbox. Exploitation requires prior compromise and crafted HTML delivery, but impacts confidentiality and integrity across Chromium-based browsers.

CISA KEV Yes · 2021-11-03⁴EPSS 0.32657 (verify live)⁵CVSS 9.6 (CISA)³CISA SSVC Exploitation: active · Automatable: no · Impact: total³

Is it exploitable?

— the evidence, ranked above the score

Reported exploitation

2 independent public reports of in-the-wild exploitation are cataloged.Distinct reporting sources (vendor, incident response, government); open them for the underlying claims.

docs.google.com ↗cisa.gov ↗Confirmed

Exploited in the wild

Listed in the CISA Known Exploited Vulnerabilities catalog (added 2021-11-03).

CISA KEV ↗Confirmed

Probability (EPSS)

EPSS 0.32657 — modeled likelihood of exploitation activity.EPSS is a daily-changing model output — open the source for today's value.

FIRST EPSS ↗High

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 Indexed DB API. 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.

CISA-ADP ↗Reported

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.

NVD ↗Reported

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.

CISA-ADP ↗Reported

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.

CISA KEV ↗CVE.org ↗Reported

WeaknessCWE-416 · Use After FreeMemory safety

Who’s exploiting it?

— attribution turns risk into urgency

Attribution 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.

Why it matters

— the attack path, told twice: adversary, then board

Front door — unauthenticated access narrative 1

Attacker

I deliver a crafted HTML page to a target user in a Chromium-based browser.

Business

User visits attacker-controlled or compromised web content, initiating the attack chain.

Keys to the kingdom — privilege/identity takeover narrative 2

Attacker

I trigger the use-after-free in the Indexed DB API to compromise the renderer process.

Business

Renderer process isolation is breached, allowing code execution beyond normal web sandbox constraints.

Lateral reach — past segmentation narrative 3

Attacker

I leverage the compromised renderer to escape the browser sandbox and access system resources.

Business

Attacker gains elevated privileges and can access sensitive user data, install malware, or pivot to system compromise.

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.

Coverage & confidence

— what we know, and what we don’t

Established (cited)

KEV listing (CISA)

EPSS probability (FIRST)

2 reported-exploitation source(s)

CVSS 9.6 — CISA-assigned (CVE.org ADP)

CISA SSVC triage disposition (CVE.org ADP)

CWE weakness mapping (NVD feed — CNA left none)

Catalogued by Chrome (CNA)

Coverage gaps — stated, not hidden

No EUVD / GCVE mirror in feed — single-authority dependency for the identifier.

EPSS & exposure are time-varying; verify live at the source.

Threat-actor attribution not established from feed data — absence of a name is not absence of compromise.

No finder is named in the public CVE record — attribution scoped to the sources checked.

Disclosure & credit²

Catalogued by ChromeCNA

Credited with finding itNo finder is named in the public CVE record or the scanned vendor advisory — attribution scoped to the sources checked.

Found an error? Propose a correction.

A correction is a cited counter-claim — it must cite a source, gets reviewed by a second human, and is never auto-applied. See the correction convention and our identity npub1j7gt9ky7sfcrjn8jjee6693dkzvk4rahs0fk2suu7968dfns62zs3mqm3y.

With JavaScript off: publish a signed kind 1111 Nostr event tagging ["r", "https://basicsecurity.net/threat/cve-2021-30633.html"], ["v", "sha256:e35def788654698dc1c1cd61b6e235075706266d98947f4dd1a9c1ec161aa43a"] (the record version), plus ["src", "<your source URL>"] and ["t", "correction"], per the correction convention. Our identity: npub1j7gt9ky7sfcrjn8jjee6693dkzvk4rahs0fk2suu7968dfns62zs3mqm3y. Cite-or-die: an event with no src is a coverage finding, not a proposal.