CASCACascade Atlas

Evidence dossier

CVE-2023-27992

The pre-authentication command injection vulnerability in the Zyxel NAS326 firmware versions prior to V5.21(AAZF.14)C0, NAS540 firmware versions prior to V5.21(AATB.11)C0, and…

Exploited in the wild (CISA KEV since Jun 23, 2023). Zyxel reports CVSS 3.1 9.8. EPSS estimates 84.2% exploit likelihood as of Aug 27, 2026.

87.0–89.7Priority evidence range
Evidence current through Aug 27, 2026, 6:09 PM UTC

As of Aug 27, 2026

Normalized restatement

The pre-authentication command injection vulnerability in the Zyxel NAS326 firmware versions prior to V5.21(AAZF.14)C0, NAS540 firmware versions prior to V5.21(AATB.11)C0, and NAS542 firmware versions prior to V5.21(ABAG.11)C0 could allow an unauthenticated attacker to execute some operating system (OS) commands remotely by sending a crafted HTTP request.

State
PUBLISHED
Published
Jun 19, 2023
Updated
Oct 21, 2025
Evidence coverage
92%

Evidence chronology

What was known when

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  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
    CVE Program

    Record text: CVE Program Container

    Inspect raw assertion
    Field
    container
    Value
    CVE Program Container
    Original evidence ↗
  3. Source dateSource date omittedFirst observed by CASCA
    Zyxel

    Record text: The pre-authentication command injection vulnerability in the Zyxel NAS326 firmware versions prior to V5.21(AAZF.14)C0, NAS540 firmware versions prior to V5.21(AATB.11)C0, and NAS542 firmware versions prior to V5.21(ABAG.11)C0 could allow an unauthenticated attacker to execute some operating system (OS) commands remotely by sending a crafted HTTP request.

    Inspect raw assertion
    Field
    container
    Value
    The pre-authentication command injection vulnerability in the Zyxel NAS326 firmware versions prior to V5.21(AAZF.14)C0, NAS540 firmware versions prior to V5.21(AATB.11)C0, and NAS542 firmware versions prior to V5.21(ABAG.11)C0 could allow an unauthenticated attacker to execute some operating system (OS) commands remotely by sending a crafted HTTP request.
    Original evidence ↗
  4. Source dateFirst observed by CASCA
    CISA KEV

    Exploitation cataloged: Zyxel Multiple NAS Devices Command Injection Vulnerability

    Inspect raw assertion
    Field
    observed_exploitation
    Value
    Zyxel Multiple NAS Devices Command Injection Vulnerability
    Original evidence ↗
  5. Source dateFirst observed by CASCA
    FIRST EPSS

    EPSS score: 84.2% probability · 99.68th percentile

    Inspect raw assertion
    Field
    model_probability
    Value
    Probability 0.841950000000; percentile 0.996770000000
    Original evidence ↗
ExploitationCatalog member

CISA KEV · catalog date Jun 23, 2023 · first observed Jul 19, 2026

Exploit likelihood84.19%

FIRST EPSS · score date Aug 27, 2026 · 99.7th percentile · first observed Aug 27, 2026

SeverityCVSS 9.8

Zyxel · 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

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 ↗
ZyxelOriginal assertion
Record text

The pre-authentication command injection vulnerability in the Zyxel NAS326 firmware versions prior to V5.21(AAZF.14)C0, NAS540 firmware versions prior to V5.21(AATB.11)C0, and NAS542 firmware versions prior to V5.21(ABAG.11)C0 could allow an unauthenticated attacker to execute some operating system (OS) commands remotely by sending a crafted HTTP request.

Inspect raw assertion
Field
container
Value
The pre-authentication command injection vulnerability in the Zyxel NAS326 firmware versions prior to V5.21(AAZF.14)C0, NAS540 firmware versions prior to V5.21(AATB.11)C0, and NAS542 firmware versions prior to V5.21(ABAG.11)C0 could allow an unauthenticated attacker to execute some operating system (OS) commands remotely by sending a crafted HTTP request.
Source dateSource date omittedFirst observed by CASCAOriginal evidence ↗
CISA KEVOriginal assertion
Exploitation cataloged

Zyxel Multiple NAS Devices Command Injection Vulnerability

Inspect raw assertion
Field
observed_exploitation
Value
Zyxel Multiple NAS Devices Command Injection Vulnerability
Source dateFirst observed by CASCAOriginal evidence ↗
FIRST EPSSOriginal assertion
EPSS score

84.2% probability · 99.68th percentile

Inspect raw assertion
Field
model_probability
Value
Probability 0.841950000000; percentile 0.996770000000
Source dateFirst observed by CASCAOriginal evidence ↗

Applicability

Cited product scope

Trace impact →
6Underlying assertions
6Canonical products
3Target assertions
3Constraint assertions

Grouped from 6 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

9 scope groups

Zyxel · source assertedZyxelNAS326 firmwareDirect source scope
Affected: < V5.21(AAZF.14)C0
Source-reported scope

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

Inspect raw assertion[{"status": "affected", "version": "< V5.21(AAZF.14)C0"}]
Zyxel · source assertedZyxelNAS540 firmwareDirect source scope
Affected: < V5.21(AATB.11)C0
Source-reported scope

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

Inspect raw assertion[{"status": "affected", "version": "< V5.21(AATB.11)C0"}]
Zyxel · source assertedZyxelNAS542 firmwareDirect source scope
Affected: < V5.21(ABAG.11)C0
Source-reported scope

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

Inspect raw assertion[{"status": "affected", "version": "< V5.21(ABAG.11)C0"}]
NVD CPE · HARDWAREzyxelnas326Environmental constraint · 1 assertions
Version not applicableCanonical identity product-bf651576568acdfc3dc579a4c64a0bb9783eea91458acad62e03f3146266c057Linked exact
Scope constrained
Inspect raw assertion
  1. cpe:2.3:h:zyxel:nas326:-:*:*:*:*:*:*:*
    Official link
    Linked exact
    Role
    Environmental constraint
    Configuration
    0 · node/1 · match 0
    Logic
    OR
    Version bounds
    No explicit bounds
    Match ID
    e0a01b19-4a91-4fbc-8447-2e854346dac5
NVD CPE · OPERATING SYSTEMzyxelnas326_firmwareVulnerable target · 1 assertions
Any version (unconstrained) (< 5.21\(aazf.14\)c0)Canonical identity product-c6d151a93544cac337f2464ac0dcf433ddb4169e8f873baebe945aa6876f626fLinked exact
Scope supported
Inspect raw assertion
  1. cpe:2.3:o:zyxel:nas326_firmware:*:*:*:*:*:*:*:*
    Official link
    Linked exact
    Role
    Vulnerable target
    Configuration
    0 · node/0 · match 0
    Logic
    OR
    Version bounds
    through excluding 5.21\(aazf.14\)c0
    Match ID
    a4a72863-e165-4a25-b53f-ee5f97236c5a
NVD CPE · HARDWAREzyxelnas540Environmental constraint · 1 assertions
Version not applicableCanonical identity product-1c152a1dd0c433303f845c38f131e5decac29d80e270f9c6923d951f9d21b408Linked exact
Scope constrained
Inspect raw assertion
  1. cpe:2.3:h:zyxel:nas540:-:*:*:*:*:*:*:*
    Official link
    Linked exact
    Role
    Environmental constraint
    Configuration
    1 · node/1 · match 0
    Logic
    OR
    Version bounds
    No explicit bounds
    Match ID
    b2f7264c-d32a-4ee9-badc-78518d762bca
NVD CPE · OPERATING SYSTEMzyxelnas540_firmwareVulnerable target · 1 assertions
Any version (unconstrained) (< 5.21\(aatb.11\)c0)Canonical identity product-d8c969fdc431fb5ce0786fa27f33a634c833b1321fdd6afd0ef33a0f4aba487eLinked exact
Scope supported
Inspect raw assertion
  1. cpe:2.3:o:zyxel:nas540_firmware:*:*:*:*:*:*:*:*
    Official link
    Linked exact
    Role
    Vulnerable target
    Configuration
    1 · node/0 · match 0
    Logic
    OR
    Version bounds
    through excluding 5.21\(aatb.11\)c0
    Match ID
    e86737df-b02e-484d-afb8-00d4f3b15330
NVD CPE · HARDWAREzyxelnas542Environmental constraint · 1 assertions
Version not applicableCanonical identity product-5ea27cf72eca89499cf908a126502ea6e72adb8df71f48cf4ae61e7e443bf27cLinked exact
Scope constrained
Inspect raw assertion
  1. cpe:2.3:h:zyxel:nas542:-:*:*:*:*:*:*:*
    Official link
    Linked exact
    Role
    Environmental constraint
    Configuration
    2 · node/1 · match 0
    Logic
    OR
    Version bounds
    No explicit bounds
    Match ID
    31c4dd0f-28d0-4bf7-897b-5eec32aa7277
NVD CPE · OPERATING SYSTEMzyxelnas542_firmwareVulnerable target · 1 assertions
Any version (unconstrained) (< 5.21\(abag.11\)c0)Canonical identity product-f16b3717078b055e905281f392735a1d4d2202ab6216028c30f08195eac3cabeLinked exact
Scope supported
Inspect raw assertion
  1. cpe:2.3:o:zyxel:nas542_firmware:*:*:*:*:*:*:*:*
    Official link
    Linked exact
    Role
    Vulnerable target
    Configuration
    2 · node/0 · match 0
    Logic
    OR
    Version bounds
    through excluding 5.21\(abag.11\)c0
    Match ID
    db6182ff-5301-474f-b324-651208839b0f

Affected-product evidence

Accepted scope and product mapping

3 canonical links · 1 source-reported links

Mapping establishedEvidence supported

vendor-b18047daaf1c9692aefa2edb7182e0b8d93a7a346ff6d96ee9c363ca18b9f5cc · product-c6d151a93544cac337f2464ac0dcf433ddb4169e8f873baebe945aa6876f626f

Source class
Nvd cpe vulnerable target
Assertions
1
Mapping revision
cpe23-exact-mapping-v1
Observed cutoff
Aug 27, 2026
Retained assertion IDs
acd1b04b-c3fe-4ecb-b127-a7a485da9caf
Mapping establishedEvidence supported

vendor-b18047daaf1c9692aefa2edb7182e0b8d93a7a346ff6d96ee9c363ca18b9f5cc · product-d8c969fdc431fb5ce0786fa27f33a634c833b1321fdd6afd0ef33a0f4aba487e

Source class
Nvd cpe vulnerable target
Assertions
1
Mapping revision
cpe23-exact-mapping-v1
Observed cutoff
Aug 27, 2026
Retained assertion IDs
d3b34619-2db5-4f05-9890-5a835e864cdc
Mapping establishedEvidence supported

vendor-b18047daaf1c9692aefa2edb7182e0b8d93a7a346ff6d96ee9c363ca18b9f5cc · product-f16b3717078b055e905281f392735a1d4d2202ab6216028c30f08195eac3cabe

Source class
Nvd cpe vulnerable target
Assertions
1
Mapping revision
cpe23-exact-mapping-v1
Observed cutoff
Aug 27, 2026
Retained assertion IDs
8ab30176-0ec5-41da-aec3-3e60dd6ff40d
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
47231275-ce46-4974-bc2d-e34762a360de6f73d85a-d0db-4d44-81f9-46e4ed2ff0f1f67cb153-b52f-407a-8457-eac4cd692fc4

Assessments

CVSS by origin

9.8
security@zyxel.com.twCVSS 3.1 · role Secondary · priority eligiblevalid_matchCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
9.8
ZyxelCVSS 3.1 · role unknown · display onlyDirect record assessment retained outside normalized eligibilityCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Direct CVE/CNA normalized decisions

9.8Priority eligible

Zyxel

CVSS 3.1 · Primary · Original assertion · rank 1

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Validation
Valid match
Recomputed
9.8
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.