Evidence used
- CISA confirms exploitation in the wild.
- The selected CVSS metric records a network-reachable, unauthenticated path with no user interaction.
- EPSS is 84.59% for the current model date.
BlackTreeCVE IntelligenceFull vulnerability report · 2026
CVE-2026-81578High confidence
PaperCut NG/MF Missing Authentication for Critical Function Vulnerability
PaperCut · NG/MF
8.8HighCVSS 4.0
Patch now
Patch availableCISA confirms exploitation in the wild and lists 2026-09-14 as the remediation due date.
R
Open reassessment dashboard →Operational reassessment
Published severity in operational context
Published severityHigh→Operational priority:Critical, raised one band.upgradedsince 31 Aug 2026
Compensating controls
- Validate the affected product branch and deploy the verified fixed release.
- Restrict the affected network interface to trusted sources where business-safe.
- Increase monitoring for the attack path and post-exploitation behaviour described in the report.
Verification
- Confirm that the asset runs PaperCut NG/MF and falls inside the recorded affected range.
- Verify the installed build against the product-specific fixed version after deployment.
- Validate exposure, authentication requirements and compensating controls in the actual environment.
- Reopen this reassessment when CVSS, KEV, EPSS, exploit evidence or remediation changes.
CISA confirms exploitation in the wild and lists 2026-09-14 as the remediation due date.
Patch available01
What, why and how
PaperCut NG/MF contains a missing authentication for critical function vulnerability which allows an unauthenticated remote attacker to modify certain system configurations. This vulnerability can be chained with CVE-2026-82078.
What
PaperCut NG/MF contains a missing authentication for critical function vulnerability which allows an unauthenticated remote attacker to modify certain system configurations. This vulnerability can be chained with CVE-2026-82078.
Why
The authentication algorithm is sound, but the implemented mechanism can be bypassed as the result of a separate weakness that is primary to the authentication error.
How
An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.
What
PaperCut NG/MF contains a missing authentication for critical function vulnerability which allows an unauthenticated remote attacker to modify certain system configurations. This vulnerability can be chained with CVE-2026-82078.
Why
The authentication algorithm is sound, but the implemented mechanism can be bypassed as the result of a separate weakness that is primary to the authentication error.
How
An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.
02
Exploit reality and attack path
CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.
Observed exploitation Confirmed in the wild
?
Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.CISA added this CVE to its Known Exploited Vulnerabilities catalogue on 2026-08-31.
Public PoC / exploit material None recorded
?
Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.No exploit-tagged reference or CISA SSVC proof-of-concept state is currently recorded. Research may still exist outside the structured feeds.
- Likely attack path
- a network path → Authentication Bypass by Primary Weakness → cause the confidentiality, integrity or availability impact described by the vendor
- Attack surface
- Network
- Privileges required
- None: unauthenticated exploitation is possible
- User interaction
- None
- Attack complexity
- Low: no specialised conditions are recorded
- Security boundary
- Not a CVSS 4.0 base metric
- Weakness
?
CWE means Common Weakness Enumeration: a standard category for the underlying weakness. - CWE-305 ↗
CWE-305: Authentication Bypass by Primary Weakness. The authentication algorithm is sound, but the implemented mechanism can be bypassed as the result of a separate weakness that is primary to the authentication error.
- CVSS vector
?
CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity. CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:H/VA:L/SC:N/SI:N/SA:NCommon Vulnerability Scoring System 4.0: the compact vector below is decoded into plain language.
AVNetworkAttack vector: The vulnerable component can be reached over a network.ACLowAttack complexity: No specialised conditions are required beyond attacker-controlled input.ATNoneAttack requirements: No additional deployment or execution condition is required.PRNonePrivileges required: The attacker does not need an account or existing privileges.UINoneUser interaction: No action by another user is required.VCLowVulnerable-system confidentiality: A successful attack can cause a limited loss.VIHighVulnerable-system integrity: A successful attack can cause a major loss.VALowVulnerable-system availability: A successful attack can cause a limited loss.SCNoneSubsequent-system confidentiality: No direct loss is represented by this metric.SINoneSubsequent-system integrity: No direct loss is represented by this metric.SANoneSubsequent-system availability: No direct loss is represented by this metric.- Post-exploitation / living off the land
- No specific living-off-the-land technique is confirmed in the structured sources. Monitor normal administration tools for activity inconsistent with the affected service's baseline.
03
Patch and workaround
Operational remediation based on structured source evidence.
- Status
?
Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change. - Patch available
- Action
- Review the linked authoritative reference and apply the recorded fixed release appropriate to the affected product branch.
- Workaround
- No verified workaround is recorded. If business-safe, reduce exposure to the affected interface and allow only trusted sources until authoritative guidance is available.
04
Evidence and provenance
Published 28 Aug 2026 · Last source change 13 Sept 2026, 23:15 UTC · CWE-305 · Authentication Bypass by Primary Weakness
CVE recordCVE.org · 5.2
CVSS sourceCNA
EPSS source FIRST · tracked since 2026-08-29
?
The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.European sourceENISA EUVD · EUVD-2026-67713
Product sourceCISA KEV
Remediation sourceCVE/CNA references
CWE sourceCNA
NVD statusNVD enriched
Core structured fields are present and their contributing authorities are shown above.
Material change intelligence
View recent updates ↗What changed after publication
- Affected versionsThe structured affected or fixed version information changed.CISA KEV ↗
- Before
- PaperCut MF/NG: < 24.1.10, 25.0.13, 26.0.5 · Fixed: An authoritative update reference is available, but the fixed version is not recorded in the structured CVE fields. Check the linked vendor advisory for the applicable release.
- After
- PaperCut MF/NG: < 24.1.10, 25.0.0 < 25.0.13, 26.0.0 < 26.0.5 · Fixed: An authoritative update reference is available, but the fixed version is not recorded in the structured CVE fields. Check the linked vendor advisory for the applicable release.
- BlackTree coverageBlackTree article coverage changed from 1 BlackTree article to 1 BlackTree article.BlackTree editorial ↗
- Before
- 1 BlackTree article
- After
- 1 BlackTree article
- Affected versionsThe structured affected or fixed version information changed.CNA ↗
- Before
- < 24.1.10, 25.0.13, 26.0.5 · Fixed: An authoritative update reference is available, but the fixed version is not recorded in the structured CVE fields. Check the linked vendor advisory for the applicable release.
- After
- PaperCut MF/NG: < 24.1.10, 25.0.13, 26.0.5 · Fixed: An authoritative update reference is available, but the fixed version is not recorded in the structured CVE fields. Check the linked vendor advisory for the applicable release.
- ENISA known-exploited stateENISA EUVD now records this CVE in its known-exploited dataset.ENISA EUVD ↗
- Before
- not listed in ENISA EUVD known-exploited dataset
- After
- listed in ENISA EUVD known-exploited dataset (EUVD-2026-67713)
- Vendor guidanceAuthoritative vendor guidance changed: added patch: cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-81578; added patch: github.com/21842; 2 further additions.papercut.com ↗
- Before
- no authoritative guidance recorded
- After
- patch: cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-81578 · patch: github.com/21842 · patch: papercut.com/security-bulletin-27-aug-2026-urgent-security-advisory · 1 more references
- Affected versionsThe structured affected or fixed version information changed.CNA ↗
- Before
- < 24.1.10, 25.0.13, 26.0.5 · Fixed: No fixed version is explicitly recorded in the structured CVE data.
- After
- < 24.1.10, 25.0.13, 26.0.5 · Fixed: An authoritative update reference is available, but the fixed version is not recorded in the structured CVE fields. Check the linked vendor advisory for the applicable release.
- Remediation statusRemediation status changed from Awaiting fix to Patch available.papercut.com ↗
- Before
- Awaiting fix
- After
- Patch available
- Public exploit evidencePublic exploit evidence changed from Public exploit reference to No public exploit.CVE.org ↗
- Before
- Public exploit reference
- After
- No public exploit
- CISA KEV stateCISA KEV now confirms exploitation in the wild.CISA KEV ↗
- Before
- listed in CISA KEV since 2026-08-28
- After
- listed in CISA KEV since 2026-08-31
- CISA KEV stateCISA KEV now confirms exploitation in the wild.CISA KEV ↗
- Before
- not listed in CISA KEV
- After
- listed in CISA KEV since 2026-08-28
- Public exploit evidencePublic exploit evidence changed from Public exploit reference to Public exploit reference.CVE.org ↗
- Before
- Public exploit reference
- After
- Public exploit reference
- Public exploit evidencePublic exploit evidence changed from No public exploit to Public exploit reference.github.com ↗
- Before
- No public exploit
- After
- Public exploit reference
- ENISA EUVD mappingEUVD-2026-67713 was added to the official ENISA EUVD mapping for this CVE.ENISA EUVD ↗
- Before
- not recorded
- After
- {"euvdId":"EUVD-2026-67713"}
- BlackTree coverageBlackTree article coverage changed from no BlackTree article to 1 BlackTree article.BlackTree editorial ↗
- Before
- no BlackTree article
- After
- 1 BlackTree article
- Catalogue recordCVE added to the BlackTree catalogue.CNA ↗
CVE published
Added to CISA KEV
Fixed release or patch reference recorded
Technical terms and abbreviations used in this report
- CVE
- Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
- CVSS
- Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
- EPSS
- Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
- CWE
- Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
- CNA
- CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
- CISA ADP
- Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
- NVD
- National Vulnerability Database: NIST's enrichment service for CVE records.
- CERT / CSIRT
- A computer security incident response team that publishes warnings or coordinates incident response.
- PoC
- Proof of concept: public material that demonstrates or helps reproduce exploitation.
- CSAF
- Common Security Advisory Framework: a machine-readable format for security advisories.
- LoTL
- Living off the land: abuse of legitimate tools or system functions during an attack.