CASCACascade Atlas

Evidence dossier

CVE-2021-21123

Insufficient data validation in File System API in Google Chrome prior to 88.0.4324.96 allowed a remote attacker to bypass filesystem restrictions via a crafted HTML page.

NVD reports CVSS 3.1 6.5. EPSS estimates 10.9% exploit likelihood as of Aug 27, 2026.

27.0–68.1Priority evidence range
Evidence current through Aug 27, 2026, 6:09 PM UTC

As of Aug 27, 2026

Normalized restatement

Insufficient data validation in File System API in Google Chrome prior to 88.0.4324.96 allowed a remote attacker to bypass filesystem restrictions via a crafted HTML page.

State
PUBLISHED
Published
Feb 9, 2021
Updated
Aug 3, 2024
Evidence coverage
55%

Evidence chronology

What was known when

Download this view's receipt →
  1. Source dateSource date omittedFirst observed by CASCA
    Chrome

    Record text: Insufficient data validation in File System API in Google Chrome prior to 88.0.4324.96 allowed a remote attacker to bypass filesystem restrictions via a crafted HTML page.

    Inspect raw assertion
    Field
    container
    Value
    Insufficient data validation in File System API in Google Chrome prior to 88.0.4324.96 allowed a remote attacker to bypass filesystem restrictions via a crafted HTML page.
    Original evidence ↗
  2. Source dateSource date omittedFirst observed by CASCA
    CVE Program

    Record text: CVE Program Container

    Inspect raw assertion
    Field
    container
    Value
    CVE Program Container
    Original evidence ↗
  3. Source dateFirst observed by CASCA
    FIRST EPSS

    EPSS score: 10.91% probability · 95.54th percentile

    Inspect raw assertion
    Field
    model_probability
    Value
    Probability 0.109100000000; percentile 0.955390000000
    Original evidence ↗
ExploitationCISA KEV: unlisted at 27 Aug 2026 18:09 UTC

The item is not listed in the bounded source as of the stated cutoff; this does not establish safety or absence outside that source.

Exploit likelihood10.91%

FIRST EPSS · score date Aug 27, 2026 · 95.5th percentile · first observed Aug 27, 2026

SeverityCVSS 6.5

NVD · CVSS 3.1 · first observed Jul 19, 2026 · same-version scores align in this snapshot

Evidence detail

Source limits and decisions

Why each evidence state has this value

casca-unknown-reasons-v1
Exploitation statusUnlisted at snapshot cutoff

The item is not listed in the bounded source as of the stated cutoff; this does not establish safety or absence outside that source.

Revision
evidence-policy-v1.1.0
Cutoff
Aug 27, 2026
Resolution
Monitor bounded source
Exploit likelihoodEvidence supported

Eligible evidence is present for this bounded claim.

Revision
evidence-policy-v1.1.0
Cutoff
Aug 27, 2026
Resolution
None
Severity assessmentEvidence supported

Eligible evidence is present for this bounded claim.

Revision
casca-direct-cvss-eligibility-v1
Cutoff
Aug 27, 2026
Resolution
None
Affected productsSource-reported scope

The cited source assertion is retained while canonical product linkage remains open.

Revision
casca-factor-d-obligations-v1
Cutoff
Aug 27, 2026
Resolution
Resolve identity

Source comparison

Who said what

ChromeOriginal assertion
Record text

Insufficient data validation in File System API in Google Chrome prior to 88.0.4324.96 allowed a remote attacker to bypass filesystem restrictions via a crafted HTML page.

Inspect raw assertion
Field
container
Value
Insufficient data validation in File System API in Google Chrome prior to 88.0.4324.96 allowed a remote attacker to bypass filesystem restrictions via a crafted HTML page.
Source dateSource date omittedFirst observed by CASCAOriginal evidence ↗
CVE ProgramDerivative copy
Record text

CVE Program Container

Inspect raw assertion
Field
container
Value
CVE Program Container
Source dateSource date omittedFirst observed by CASCAOriginal evidence ↗
FIRST EPSSOriginal assertion
EPSS score

10.91% probability · 95.54th percentile

Inspect raw assertion
Field
model_probability
Value
Probability 0.109100000000; percentile 0.955390000000
Source dateFirst observed by CASCAOriginal evidence ↗

Applicability

Cited product scope

Trace impact →
2Underlying assertions
2Canonical products
2Target assertions
0Constraint assertions

Grouped from 1 configuration nodes in this exact snapshot. Visual grouping is navigational; asset exposure and root cause require cited evidence.

Identity source boundaries
  • Cpe dictionary1,775,266 records · observed through 2026-07-21T06:45:29.809Z27d65b0f-b718-4b4f-bb79-c47c68d09dfa
  • Cpe match643,502 records · observed through 2026-07-21T08:13:17.697Z955dae73-7302-438b-aee1-058d7cc5d48e

3 scope groups

Chrome · source assertedGoogleChromeDirect source scope
Affected: unspecified to before 88.0.4324.96 (custom comparison)
Source-reported scope

Canonical linkage remains open; the cited source assertion is retained below.

Inspect raw assertion[{"status": "affected", "version": "unspecified", "lessThan": "88.0.4324.96", "versionType": "custom"}]
NVD CPE · APPLICATIONgooglechromeVulnerable target · 1 assertions
Any version (unconstrained) (< 88.0.4324.96)Canonical identity product-6239ec405e2e1cdd75fd8ed01bb6845a448ecca3c3edcc8b0c5ccc2adb8b6bcdLinked exact
Scope supported
Inspect raw assertion
  1. cpe:2.3:a:google:chrome:*:*:*:*:*:*:*:*
    Official link
    Linked exact
    Role
    Vulnerable target
    Configuration
    0 · node/0 · match 0
    Logic
    OR
    Version bounds
    through excluding 88.0.4324.96
    Match ID
    565ed6b8-8f41-4e79-a280-33cb321e607f
NVD CPE · APPLICATIONmicrosoftedge_chromiumVulnerable target · 1 assertions
Any version (unconstrained) (< 88.0.705.50)Canonical identity product-151fa43ce688e686b0979b3df6d6fc924c7ee990e167f81db3729dc080ad5098Linked exact
Scope supported
Inspect raw assertion
  1. cpe:2.3:a:microsoft:edge_chromium:*:*:*:*:*:*:*:*
    Official link
    Linked exact
    Role
    Vulnerable target
    Configuration
    0 · node/0 · match 1
    Logic
    OR
    Version bounds
    through excluding 88.0.705.50
    Match ID
    f4045760-df4a-4728-9b52-0280fc45c05d

Affected-product evidence

Accepted scope and product mapping

2 canonical links · 1 source-reported links

Mapping establishedEvidence supported

vendor-01299a5a765aea70faa05f2d06e0c26a5d498fd34553e868d89e8a43b31864db · product-151fa43ce688e686b0979b3df6d6fc924c7ee990e167f81db3729dc080ad5098

Source class
Nvd cpe vulnerable target
Assertions
1
Mapping revision
cpe23-exact-mapping-v1
Observed cutoff
Aug 27, 2026
Retained assertion IDs
62b11ec5-7841-424e-ab7a-7053a3cf9d1a
Mapping establishedEvidence supported

vendor-88869ec57256fdf5d0b9ffd6f3d141ad371acdd6f81405ddb6c5e9e45b10869c · product-6239ec405e2e1cdd75fd8ed01bb6845a448ecca3c3edcc8b0c5ccc2adb8b6bcd

Source class
Nvd cpe vulnerable target
Assertions
1
Mapping revision
cpe23-exact-mapping-v1
Observed cutoff
Aug 27, 2026
Retained assertion IDs
ed67906c-5197-4938-bc9f-21fe22f95820
Source-reported scopeSource-reported scope

Canonical linkage remains open; the cited source assertion is retained below.

Vendor specified only by source · Product specified only by source

Source class
Direct cve affected
Assertions
1
Mapping revision
cpe23-exact-mapping-v1
Observed cutoff
Aug 27, 2026
Retained assertion IDs
691c2722-d9d4-4839-8033-d9fefe5125cc

Assessments

CVSS by origin

6.5
NVDCVSS 3.1 · role Primary · priority eligiblevalid_matchCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N
4.3
NVDCVSS 2.0 · role Primary · priority eligiblevalid_matchAV:N/AC:M/Au:N/C:N/I:P/A:N

Evidence boundaries

  • CISA KEV catalog silence leaves exploitation status unassessed.
  • EPSS is a dated model probability and not an individual-environment prediction.
  • Affected or fixed status applies only to the exact cited product and version scope; remaining scope stays source-scoped.
  • NVD-carried upstream facts remain derivative; independent corroboration requires a separately authored source.
  • Only NVD metrics validated under the generation-bound calculator are Public Priority eligible; direct CVE record metrics remain display-only.
  • NVD CVSS source eligibility is closed: NVD-authored, exact record-source, or registered same-CVE container origin; unmapped sources remain display-only.
  • Core replay supports the active and immediately prior generation; retrospective valid-at replay is deferred.
  • OSV aggregation and OSV-converted NVD material are not independent corroboration.
  • Red Hat facts are vendor assertions for the exact supplied products.
  • Nonmembership and not-yet-observed states are not proof of safety.