CASCACascade Atlas

Evidence dossier

CVE-2021-1879

This issue was addressed by improved management of object lifetimes.

Exploited in the wild (CISA KEV since Nov 3, 2021). NVD reports CVSS 3.1 6.1. EPSS estimates 7.1% exploit likelihood as of Aug 27, 2026.

64.7–67.4Priority evidence range
Evidence current through Aug 27, 2026, 6:09 PM UTC

As of Aug 27, 2026

Normalized restatement

This issue was addressed by improved management of object lifetimes. This issue is fixed in iOS 12.5.2, iOS 14.4.2 and iPadOS 14.4.2, watchOS 7.3.3. Processing maliciously crafted web content may lead to universal cross site scripting. Apple is aware of a report that this issue may have been actively exploited..

State
PUBLISHED
Published
Apr 2, 2021
Updated
Oct 21, 2025
Evidence coverage
93%

Evidence chronology

What was known when

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  1. Source dateSource date omittedFirst observed by CASCA
    apple

    Record text: This issue was addressed by improved management of object lifetimes. This issue is fixed in iOS 12.5.2, iOS 14.4.2 and iPadOS 14.4.2, watchOS 7.3.3. Processing maliciously crafted web content may lead to universal cross site scripting. Apple is aware of a report that this issue may have been actively exploited..

    Inspect raw assertion
    Field
    container
    Value
    This issue was addressed by improved management of object lifetimes. This issue is fixed in iOS 12.5.2, iOS 14.4.2 and iPadOS 14.4.2, watchOS 7.3.3. Processing maliciously crafted web content may lead to universal cross site scripting. Apple is aware of a report that this issue may have been actively exploited..
    Original evidence ↗
  2. Source dateSource date omittedFirst observed by CASCA
    CISA-ADP

    Record text: CISA ADP Vulnrichment

    Inspect raw assertion
    Field
    container
    Value
    CISA ADP Vulnrichment
    Original evidence ↗
  3. 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 ↗
  4. Source dateFirst observed by CASCA
    CISA KEV

    Exploitation cataloged: Apple iOS, iPadOS, and watchOS WebKit Cross-Site Scripting (XSS) Vulnerability

    Inspect raw assertion
    Field
    observed_exploitation
    Value
    Apple iOS, iPadOS, and watchOS WebKit Cross-Site Scripting (XSS) Vulnerability
    Original evidence ↗
  5. Source dateFirst observed by CASCA
    FIRST EPSS

    EPSS score: 7.08% probability · 93.74th percentile

    Inspect raw assertion
    Field
    model_probability
    Value
    Probability 0.070820000000; percentile 0.937390000000
    Original evidence ↗
ExploitationCatalog member

CISA KEV · catalog date Nov 3, 2021 · first observed Jul 19, 2026

Exploit likelihood7.08%

FIRST EPSS · score date Aug 27, 2026 · 93.7th percentile · first observed Aug 27, 2026

SeverityCVSS 6.1

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 statusEvidence supported

Eligible evidence is present for this bounded claim.

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

appleOriginal assertion
Record text

This issue was addressed by improved management of object lifetimes. This issue is fixed in iOS 12.5.2, iOS 14.4.2 and iPadOS 14.4.2, watchOS 7.3.3. Processing maliciously crafted web content may lead to universal cross site scripting. Apple is aware of a report that this issue may have been actively exploited..

Inspect raw assertion
Field
container
Value
This issue was addressed by improved management of object lifetimes. This issue is fixed in iOS 12.5.2, iOS 14.4.2 and iPadOS 14.4.2, watchOS 7.3.3. Processing maliciously crafted web content may lead to universal cross site scripting. Apple is aware of a report that this issue may have been actively exploited..
Source dateSource date omittedFirst observed by CASCAOriginal evidence ↗
CISA-ADPIndependent enrichment
Record text

CISA ADP Vulnrichment

Inspect raw assertion
Field
container
Value
CISA ADP Vulnrichment
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 ↗
CISA KEVOriginal assertion
Exploitation cataloged

Apple iOS, iPadOS, and watchOS WebKit Cross-Site Scripting (XSS) Vulnerability

Inspect raw assertion
Field
observed_exploitation
Value
Apple iOS, iPadOS, and watchOS WebKit Cross-Site Scripting (XSS) Vulnerability
Source dateFirst observed by CASCAOriginal evidence ↗
FIRST EPSSOriginal assertion
EPSS score

7.08% probability · 93.74th percentile

Inspect raw assertion
Field
model_probability
Value
Probability 0.070820000000; percentile 0.937390000000
Source dateFirst observed by CASCAOriginal evidence ↗

Applicability

Cited product scope

Trace impact →
4Underlying assertions
3Canonical products
4Target 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

6 scope groups

apple · source assertedAppleiOSDirect source scope
Affected: unspecified to before 12.5 (custom comparison)
Source-reported scope

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

Inspect raw assertion[{"status": "affected", "version": "unspecified", "lessThan": "12.5", "versionType": "custom"}]
apple · source assertedAppleiOS and iPadOSDirect source scope
Affected: unspecified to before 14.4 (custom comparison)
Source-reported scope

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

Inspect raw assertion[{"status": "affected", "version": "unspecified", "lessThan": "14.4", "versionType": "custom"}]
apple · source assertedApplewatchOSDirect source scope
Affected: unspecified to before 7.3 (custom comparison)
Source-reported scope

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

Inspect raw assertion[{"status": "affected", "version": "unspecified", "lessThan": "7.3", "versionType": "custom"}]
NVD CPE · OPERATING SYSTEMappleipadosVulnerable target · 1 assertions
Any version (unconstrained) (< 14.4.2)Canonical identity product-8e7094ac066248cd4828b6ec8e3a96d010ed1c68f6083af46638775d737da0adLinked exact
Scope supported
Inspect raw assertion
  1. cpe:2.3:o:apple:ipados:*:*:*:*:*:*:*:*
    Official link
    Linked exact
    Role
    Vulnerable target
    Configuration
    0 · node/0 · match 0
    Logic
    OR
    Version bounds
    through excluding 14.4.2
    Match ID
    20b9f5c7-15b9-44f6-8167-2532394c8346
NVD CPE · OPERATING SYSTEMappleiphone_osVulnerable target · 2 assertions
Any version (unconstrained) (< 12.5.2); Any version (unconstrained) (>= 13.0, < 14.4.2)Canonical identity product-665d7155d02581979844685e7fca6c2680af997f9200af455887b1c71c483272Linked exact
Scope supported
Inspect raw assertions
  1. cpe:2.3:o:apple:iphone_os:*:*:*:*:*:*:*:*
    Official link
    Linked exact
    Role
    Vulnerable target
    Configuration
    0 · node/0 · match 2
    Logic
    OR
    Version bounds
    from including 13.0; through excluding 14.4.2
    Match ID
    5a5dbdbf-b828-416d-b69c-f70f1078c13a
  2. cpe:2.3:o:apple:iphone_os:*:*:*:*:*:*:*:*
    Official link
    Linked exact
    Role
    Vulnerable target
    Configuration
    0 · node/0 · match 1
    Logic
    OR
    Version bounds
    through excluding 12.5.2
    Match ID
    7fe2035d-b101-455f-b591-c2eec59ace9d
NVD CPE · OPERATING SYSTEMapplewatchosVulnerable target · 1 assertions
Any version (unconstrained) (< 7.3.3)Canonical identity product-1b28e85eba5cb27cd93d563b4ea63a555b916484cee543c65fdbe57d529fc0d1Linked exact
Scope supported
Inspect raw assertion
  1. cpe:2.3:o:apple:watchos:*:*:*:*:*:*:*:*
    Official link
    Linked exact
    Role
    Vulnerable target
    Configuration
    0 · node/0 · match 3
    Logic
    OR
    Version bounds
    through excluding 7.3.3
    Match ID
    d8059bac-7c40-446d-aa16-a5ea5eebcea8

Affected-product evidence

Accepted scope and product mapping

3 canonical links · 1 source-reported links

Mapping establishedEvidence supported

vendor-d6ed6f1e35de2e16a8a10f2ae364dab009bb2afadd609071b20da24d60ce2829 · product-1b28e85eba5cb27cd93d563b4ea63a555b916484cee543c65fdbe57d529fc0d1

Source class
Nvd cpe vulnerable target
Assertions
1
Mapping revision
cpe23-exact-mapping-v1
Observed cutoff
Aug 27, 2026
Retained assertion IDs
c82f31b5-eaa2-4674-8154-1b031c53a0be
Mapping establishedEvidence supported

vendor-d6ed6f1e35de2e16a8a10f2ae364dab009bb2afadd609071b20da24d60ce2829 · product-665d7155d02581979844685e7fca6c2680af997f9200af455887b1c71c483272

Source class
Nvd cpe vulnerable target
Assertions
2
Mapping revision
cpe23-exact-mapping-v1
Observed cutoff
Aug 27, 2026
Retained assertion IDs
afc1d2aa-60c7-49ad-bad3-30a7938001f9c33ad0a5-0237-4e49-bbe0-f3baac01ab00
Mapping establishedEvidence supported

vendor-d6ed6f1e35de2e16a8a10f2ae364dab009bb2afadd609071b20da24d60ce2829 · product-8e7094ac066248cd4828b6ec8e3a96d010ed1c68f6083af46638775d737da0ad

Source class
Nvd cpe vulnerable target
Assertions
1
Mapping revision
cpe23-exact-mapping-v1
Observed cutoff
Aug 27, 2026
Retained assertion IDs
17eae1a8-098e-49d2-abe3-c921db3b87cc
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
3
Mapping revision
cpe23-exact-mapping-v1
Observed cutoff
Aug 27, 2026
Retained assertion IDs
3b0da551-d80a-4e63-a927-a041c1198ba7616433a5-3efe-462c-9dc9-ab27c8ea4c5980c2efe4-480b-4341-8f46-b1ccb05fcec0

Assessments

CVSS by origin

6.1
NVDCVSS 3.1 · role Primary · priority eligiblevalid_matchCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
4.3
NVDCVSS 2.0 · role Primary · priority eligiblevalid_matchAV:N/AC:M/Au:N/C:N/I:P/A:N
6.1
CVE Program sourceCVSS 3.1 · role Secondary · priority eligiblevalid_matchCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
6.1
CISA-ADPCVSS 3.1 · role unknown · display onlyDirect record assessment retained outside normalized eligibilityCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Direct CVE/CNA normalized decisions

6.1Priority eligible

CISA-ADP

CVSS 3.1 · Secondary · Independent enrichment · rank 2

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Validation
Valid match
Recomputed
6.1
Decision reason
Evidence supported
Policy
casca-direct-cvss-eligibility-v1

Assessments are retained side by side under closed precedence. Cascade never averages CVSS.

Evidence boundaries

  • KEV membership is authoritative for the catalog, not proof of exposure in any environment.
  • 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.