CASCACascade Atlas

Evidence dossier

CVE-2025-66376

Zimbra Collaboration (ZCS) 10 before 10.0.18 and 10.1 before 10.1.13 allows Classic UI stored XSS via Cascading Style Sheets (CSS) @import directives in an HTML e-mail message.

Exploited in the wild (CISA KEV since Mar 18, 2026). NVD reports CVSS 3.1 6.1. Severity assessments differ within at least one CVSS version. EPSS estimates 19.3% exploit likelihood as of Aug 27, 2026.

66.7–71.0Priority evidence range
Evidence current through Aug 27, 2026, 6:09 PM UTC

As of Aug 27, 2026

Normalized restatement

Zimbra Collaboration (ZCS) 10 before 10.0.18 and 10.1 before 10.1.13 allows Classic UI stored XSS via Cascading Style Sheets (CSS) @import directives in an HTML e-mail message.

State
PUBLISHED
Published
Jan 5, 2026
Updated
Mar 19, 2026
Evidence coverage
82%

Evidence chronology

What was known when

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

    Record text: Zimbra Collaboration (ZCS) 10 before 10.0.18 and 10.1 before 10.1.13 allows Classic UI stored XSS via Cascading Style Sheets (CSS) @import directives in an HTML e-mail message.

    Inspect raw assertion
    Field
    container
    Value
    Zimbra Collaboration (ZCS) 10 before 10.0.18 and 10.1 before 10.1.13 allows Classic UI stored XSS via Cascading Style Sheets (CSS) @import directives in an HTML e-mail message.
    Original evidence ↗
  3. Source dateFirst observed by CASCA
    CISA KEV

    Exploitation cataloged: Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting Vulnerability

    Inspect raw assertion
    Field
    observed_exploitation
    Value
    Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting Vulnerability
    Original evidence ↗
  4. Source dateFirst observed by CASCA
    FIRST EPSS

    EPSS score: 19.3% probability · 97.14th percentile

    Inspect raw assertion
    Field
    model_probability
    Value
    Probability 0.193040000000; percentile 0.971390000000
    Original evidence ↗

Assessments differ

NVD6.1CVSS 3.1 · source date omitted
cve@mitre.org7.2CVSS 3.1 · source date omitted

Values are shown separately by source and CVSS version.

ExploitationCatalog member

CISA KEV · catalog date Mar 18, 2026 · first observed Jul 19, 2026

Exploit likelihood19.30%

FIRST EPSS · score date Aug 27, 2026 · 97.1th percentile · first observed Aug 27, 2026

SeverityAssessments differ

NVD · CVSS 3.1 · first observed Jul 19, 2026 · values shown separately below

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 assessmentAssessments differ

Eligible assertions materially conflict and remain visible side by side.

Revision
casca-direct-cvss-eligibility-v1
Cutoff
Aug 27, 2026
Resolution
Resolve conflict
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

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 ↗
mitreOriginal assertion
Record text

Zimbra Collaboration (ZCS) 10 before 10.0.18 and 10.1 before 10.1.13 allows Classic UI stored XSS via Cascading Style Sheets (CSS) @import directives in an HTML e-mail message.

Inspect raw assertion
Field
container
Value
Zimbra Collaboration (ZCS) 10 before 10.0.18 and 10.1 before 10.1.13 allows Classic UI stored XSS via Cascading Style Sheets (CSS) @import directives in an HTML e-mail message.
Source dateSource date omittedFirst observed by CASCAOriginal evidence ↗
CISA KEVOriginal assertion
Exploitation cataloged

Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting Vulnerability

Inspect raw assertion
Field
observed_exploitation
Value
Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting Vulnerability
Source dateFirst observed by CASCAOriginal evidence ↗
FIRST EPSSOriginal assertion
EPSS score

19.3% probability · 97.14th percentile

Inspect raw assertion
Field
model_probability
Value
Probability 0.193040000000; percentile 0.971390000000
Source dateFirst observed by CASCAOriginal evidence ↗

Applicability

Cited product scope

Trace impact →
2Underlying assertions
1Canonical 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

2 scope groups

mitre · source assertedZimbraCollaborationDirect source scope
Affected: 10.0 to before 10.0.18 (custom comparison)Affected: 10.1 to before 10.1.13 (custom comparison)
Source-reported scope

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

Inspect raw assertion[{"status": "affected", "version": "10.0", "lessThan": "10.0.18", "versionType": "custom"}, {"status": "affected", "version": "10.1", "lessThan": "10.1.13", "versionType": "custom"}]
NVD CPE · APPLICATIONsynacorzimbra_collaboration_suiteVulnerable target · 2 assertions
Any version (unconstrained) (>= 10.0.0, < 10.0.18); Any version (unconstrained) (>= 10.1.0, < 10.1.13)Canonical identity product-4e282fadbbcc212039ad71a0e7de43d3b9757c46bbe8fd5c086551b6c01bb56aLinked exact
Scope supported
Inspect raw assertions
  1. cpe:2.3:a:synacor:zimbra_collaboration_suite:*:*:*:*:*:*:*:*
    Official link
    Linked exact
    Role
    Vulnerable target
    Configuration
    0 · node/0 · match 1
    Logic
    OR
    Version bounds
    from including 10.1.0; through excluding 10.1.13
    Match ID
    7c3f6b1e-1671-461b-a093-7b6854c227fe
  2. cpe:2.3:a:synacor:zimbra_collaboration_suite:*:*:*:*:*:*:*:*
    Official link
    Linked exact
    Role
    Vulnerable target
    Configuration
    0 · node/0 · match 0
    Logic
    OR
    Version bounds
    from including 10.0.0; through excluding 10.0.18
    Match ID
    7d423db3-fcd4-445f-a778-bc5f83e01953

Affected-product evidence

Accepted scope and product mapping

1 canonical links · 1 source-reported links

Mapping establishedEvidence supported

vendor-3d8b4bf53132b048a53e1d14e1e14dd5a07b75f8055a3624a0041d87433ca594 · product-4e282fadbbcc212039ad71a0e7de43d3b9757c46bbe8fd5c086551b6c01bb56a

Source class
Nvd cpe vulnerable target
Assertions
2
Mapping revision
cpe23-exact-mapping-v1
Observed cutoff
Aug 27, 2026
Retained assertion IDs
883fb46f-2cd5-41e9-a84b-a1119cfe574a9308682e-ab9a-4e22-9113-2decdc60b086
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
b7e8580a-9b03-4eef-9f19-e38ba130285c

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
7.2
cve@mitre.orgCVSS 3.1 · role Secondary · priority eligiblevalid_matchCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N
7.2
mitreCVSS 3.1 · role unknown · display onlyDirect record assessment retained outside normalized eligibilityCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N

Direct CVE/CNA normalized decisions

7.2Priority eligible

mitre

CVSS 3.1 · Primary · Original assertion · rank 1

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N
Validation
Valid match
Recomputed
7.2
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.