CASCACascade Atlas

Evidence dossier

CVE-2026-81578

PaperCut MF/NG: Authentication Bypass

Exploited in the wild (CISA KEV since Aug 31, 2026). PaperCut reports CVSS 4.0 8.8. EPSS estimates 85.6% exploit likelihood as of Oct 22, 2026.

80.5–88.4Priority evidence range
Evidence through Oct 22, 2026, 6:07 PM UTC

As of Oct 22, 2026

Normalized restatement

An improper access control vulnerability exists in the web management interface of PaperCut MF and PaperCut NG. Under specific conditions, unauthenticated remote requests targeting administrative functions can trigger backend actions prior to the completion of access validation checks. This allows an unauthenticated remote attacker to modify certain system configurations.

State
PUBLISHED
Published
Aug 28, 2026
Updated
Sep 13, 2026
Evidence coverage
85%

Evidence chronology

What was known when

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  1. Source dateFirst observed by CASCA
    CISA KEV

    Exploitation cataloged: PaperCut NG/MF Missing Authentication for Critical Function Vulnerability

    Inspect raw assertion
    Field
    observed_exploitation
    Value
    PaperCut NG/MF Missing Authentication for Critical Function Vulnerability
    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
    PaperCut

    Record text: PaperCut MF/NG: Authentication Bypass

    Inspect raw assertion
    Field
    container
    Value
    PaperCut MF/NG: Authentication Bypass
    Original evidence ↗
  4. Source dateFirst observed by CASCA
    FIRST EPSS

    EPSS score: 85.58% probability · 99.73th percentile

    Inspect raw assertion
    Field
    model_probability
    Value
    Probability 0.855810000000; percentile 0.997260000000
    Original evidence ↗
ExploitationCatalog member

CISA KEV · catalog date Aug 31, 2026 · first observed Sep 1, 2026

Exploit likelihood85.58%

FIRST EPSS · score date Oct 22, 2026 · 99.7th percentile · first observed Oct 22, 2026

SeverityCVSS 8.8

PaperCut · CVSS 4.0 · first observed Sep 14, 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 statusLast verified source snapshot retained

The last verified source boundary remains in force for this claim.

Revision
evidence-policy-v1.1.0
Cutoff
Oct 22, 2026
Resolution
Review source contract
Exploit likelihoodEvidence supported

Eligible evidence is present for this bounded claim.

Revision
evidence-policy-v1.1.0
Cutoff
Oct 22, 2026
Resolution
None
Severity assessmentEvidence supported

Eligible evidence is present for this bounded claim.

Revision
casca-direct-cvss-eligibility-v1
Cutoff
Oct 22, 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
Oct 22, 2026
Resolution
Resolve identity

Source comparison

Who said what

CISA KEVOriginal assertion
Exploitation cataloged

PaperCut NG/MF Missing Authentication for Critical Function Vulnerability

Inspect raw assertion
Field
observed_exploitation
Value
PaperCut NG/MF Missing Authentication for Critical Function Vulnerability
Source dateFirst 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 ↗
PaperCutOriginal assertion
Record text

PaperCut MF/NG: Authentication Bypass

Inspect raw assertion
Field
container
Value
PaperCut MF/NG: Authentication Bypass
Source dateSource date omittedFirst observed by CASCAOriginal evidence ↗
FIRST EPSSOriginal assertion
EPSS score

85.58% probability · 99.73th percentile

Inspect raw assertion
Field
model_probability
Value
Probability 0.855810000000; percentile 0.997260000000
Source dateFirst observed by CASCAOriginal evidence ↗

Applicability

Cited product scope

Trace impact →

7 scope groups

PaperCut · source assertedPaperCutPaperCut MF/NGDirect source scope
Affected: 0 to before 24.1.10 (semver comparison)Affected: 25.0.0 to before 25.0.13 (semver comparison)Affected: 26.0.0 to before 26.0.5 (semver comparison)
Source-reported scope

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

Inspect raw assertion[{"status": "affected", "version": "0", "lessThan": "24.1.10", "versionType": "semver"}, {"status": "affected", "version": "25.0.0", "lessThan": "25.0.13", "versionType": "semver"}, {"status": "affected", "version": "26.0.0", "lessThan": "26.0.5", "versionType": "semver"}]
NVD · source assertedVendor unspecified by sourceProduct unspecified by sourceDirect source scope
Version bounds not stated
Scope supported
Inspect raw assertioncpe:2.3:a:papercut:papercut_mf:*:*:*:*:*:*:*:*; end excluding 24.1.9
NVD · source assertedVendor unspecified by sourceProduct unspecified by sourceDirect source scope
Version bounds not stated
Scope supported
Inspect raw assertioncpe:2.3:a:papercut:papercut_mf:*:*:*:*:*:*:*:*; start including 25.0.2; end excluding 25.0.12
NVD · source assertedVendor unspecified by sourceProduct unspecified by sourceDirect source scope
Version bounds not stated
Scope supported
Inspect raw assertioncpe:2.3:a:papercut:papercut_mf:*:*:*:*:*:*:*:*; start including 26.0.2; end excluding 26.0.4
NVD · source assertedVendor unspecified by sourceProduct unspecified by sourceDirect source scope
Version bounds not stated
Scope supported
Inspect raw assertioncpe:2.3:a:papercut:papercut_ng:*:*:*:*:*:*:*:*; end excluding 24.1.9
NVD · source assertedVendor unspecified by sourceProduct unspecified by sourceDirect source scope
Version bounds not stated
Scope supported
Inspect raw assertioncpe:2.3:a:papercut:papercut_ng:*:*:*:*:*:*:*:*; start including 25.0.2; end excluding 25.0.12
NVD · source assertedVendor unspecified by sourceProduct unspecified by sourceDirect source scope
Version bounds not stated
Scope supported
Inspect raw assertioncpe:2.3:a:papercut:papercut_ng:*:*:*:*:*:*:*:*; start including 26.0.2; end excluding 26.0.4

Affected-product evidence

Accepted scope and product mapping

0 canonical links · 2 source-reported links

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
Oct 22, 2026
Retained assertion IDs
1d0c1a73-758c-4d76-9daa-2c71e843ef4c
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
Nvd cpe vulnerable target
Assertions
6
Mapping revision
cpe23-exact-mapping-v1
Observed cutoff
Oct 22, 2026
Retained assertion IDs
11e8201a-a5d6-4f59-9e75-b3b696e6ce551ca441d9-29c8-4702-9f72-858111dea6853c47c12e-413f-4dba-8d18-dfc7a64955c0889b6c84-5af9-4332-8d22-33cbd91b0222b4e53c17-d40b-454c-a1db-e7b7364ae360d7fdcdac-f1b4-4729-bc71-d02381707fb2

Assessments

CVSS by origin

9.8
NVDCVSS 3.1 · role Primary · priority eligiblevalid_matchCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
8.8
CVE Program sourceCVSS 4.0 · role Secondary · priority eligiblevalid_matchCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:H/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
8.8
PaperCutCVSS 4.0 · role unknown · display onlyDirect record assessment retained outside normalized eligibilityCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:H/VA:L/SC:N/SI:N/SA:N

Direct CVE/CNA normalized decisions

8.8Priority eligible

PaperCut

CVSS 4.0 · Primary · Original assertion · rank 1

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:H/VA:L/SC:N/SI:N/SA:N
Validation
Valid match
Recomputed
8.8
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.