CriticalCVE-2026-82078

    PaperCut MF/NG: Unsafe Dynamic Class Loading in Database Connector (CVE-2026-82078)

    Published Last modified In CISA KEV since Sources: CVE.org

    What is affected, what to do

    An unsafe dynamic class loading vulnerability exists in the database connection utilities of PaperCut MF and PaperCut NG. The application instantiates database driver classes based on configurable driver names without validating against an allowlist of approved drivers.

    The vulnerability is being actively exploited; treat it as a priority. Update PaperCut MF/NG to version 24.1.10, PaperCut MF/NG to version 25.0.13, PaperCut MF/NG to version 26.0.5. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • PaperCut MF/NG lt *..24.1.10
    • PaperCut MF/NG lt 25.0.0..25.0.13
    • PaperCut MF/NG lt 26.0.0..26.0.5
    Fixed in
    • PaperCut MF/NG 24.1.10
    • PaperCut MF/NG 25.0.13
    • PaperCut MF/NG 26.0.5

    Not sure whether and how you are affected? Ask a question about this vulnerability

    Metrics

    9.4

    Priority

    XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

    Source: Vendor (CNA), CVSS v4

    9.1

    CVSS v3

    Severity Critical on the scale from 0 to 10.

    Source: CVE.org

    60.9 %

    EPSS score

    High — model estimates ≥ 50% chance of real-world exploitation within 30 days.

    Source: FIRST EPSS, percentile 99.15

    Show all metrics
    Severity
    Critical
    Priority (0–325)

    The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?

    Read in glossary
    250.55 Methodology
    Exploit maturity

    An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.

    Read in glossary
    actively exploitedSource: VulnCheck KEV (opens in a new tab), CIRCL Sightings How we classify
    XIEM Effective CVSS

    XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.

    Read in glossary
    9.4 Methodology
    CVSS v3

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    9.1
    CVSS v4

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    9.4
    EPSS score

    The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.

    Read in glossary
    60.9 %
    High — model estimates ≥ 50% chance of real-world exploitation within 30 days.
    EPSS percentile

    The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.

    Read in glossary
    99.15
    Critical — this CVE ranks in the top fifth of all CVEs scored today (rank ≥ 80%).
    KEV status

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    Actively exploited
    Published
    In CISA KEV since

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    CWE

    CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.

    Read in glossary
    CWE-470

    Response and mitigation

    Why act now?

    Prioritisation rationale

    This CVE is on KEV because it turns the PaperCut server into a reliable code-execution target under the service account, and CISA explicitly flags that it can be chained with CVE-2026-81578, effectively neutralising the „high privileges required" entry barrier. Exploitation likelihood sits among the very highest EPSS has tracked recently, and PaperCut deployments are common in universities, public administration, healthcare and other NIS2-regulated verticals — frequently exposed to the internet to support mobile print. Score it P1 whenever the admin UI is reachable from non-management networks or the server has unrestricted egress; otherwise P2 with a hard 72-hour patch window. CISA has not flagged ransomware use for this specific CVE, but prior PaperCut vulnerabilities moved from KEV listing to active ransomware deployment within weeks.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Patch PaperCut NG/MF to a vendor-fixed release — every build in 24.1.9, 25.0.2–25.0.12 and 26.0.2–26.0.4 is affected; take the exact target version from the current PaperCut security bulletin and track it via change record.
      • Remove the admin web UI (default TCP/9191 HTTP, TCP/9192 HTTPS) from the public internet immediately; restrict it to an admin jump-host segment. Print service ports (TCP/9100, IPP 631) stay functional but must not be internet-reachable either.
      • Rotate admin credentials and enforce MFA; the CVE requires high privileges on paper, but those same credentials are the pivot target when chained with CVE-2026-81578. Review every admin login of the last 30 days for plausibility.
      • Audit the database driver configuration parameters (print.database.*) in the admin UI: only legitimate JDBC driver classes such as org.postgresql.Driver or com.microsoft.sqlserver.jdbc.SQLServerDriver may be set. Anything else is a compromise indicator.
      • Inventory the PaperCut server classpath: diff [app-path]/server/lib, lib-ext and any custom directory against a hash baseline from a clean install; flag unexpected JAR/CLASS files.
      • If patching cannot land inside the change window: put the PaperCut service into maintenance mode, firewall-block all external admin access and put IR on standby.

    2. Runbook step 2

      Mitigation layers

      • Network segmentation: place the PaperCut server in a dedicated VLAN with default-deny egress; allow outbound only to printers, LDAP/AD, DB backend and the licence endpoint (update.papercut.com). Most RCE payloads need C2 egress — default-deny breaks the second stage.
      • Reverse proxy / WAF in front of 9191/9192: restrict admin paths (/app?service=page/* and /rpc/api/*) to known source IPs; log and block POST requests whose configuration parameters match a Java fully-qualified-class-name pattern ([a-zA-Z0-9_$]+\.[A-Z][a-zA-Z0-9_$]+(\.[A-Z][a-zA-Z0-9_$]+)+).
      • Host hardening: run the PaperCut service under a dedicated non-privileged service account (Windows: never LOCAL SYSTEM; Linux: a dedicated papercut user without shell). Tighten filesystem ACLs on server/lib so the service account cannot write there — this prevents dropping a malicious JAR into the classpath.
      • IAM / least privilege: split the admin role onto named accounts, disable the shared „admin" account, cut session timeout to 15 minutes, and enforce MFA via SAML/OIDC SSO.
      • Configuration monitoring: watch print.database.driver, print.database.url, auth.* and any custom-report-script parameter via FIM on server.properties plus API audit; alert on any change outside a scheduled change window.
      • Freeze a known-good backup of the configuration and the classpath directory so you have a defensible comparison baseline after any incident.

    3. Runbook step 3

      Detection rules

      • PaperCut web access logs (server/logs/server.log, access.log): POST to /rpc/api/* or /app?service=* carrying parameters with fully qualified Java class names. Sigma shape: selection: cs-uri-stem|contains: '/rpc/api' AND cs-method: POST AND cs-uri-query|re: '([a-z]+\.){2,}[A-Z][A-Za-z]+'.
      • Sysmon EID 1 / auditd execve: child processes of pc-app.exe or java within the PaperCut process tree spawning cmd.exe, powershell.exe, /bin/sh, bash, wget, curl, certutil or bitsadmin — the classic post-exploitation chain.
      • Sysmon EID 11 / auditd file watch: new .jar or .class files appearing under [papercut]/server/lib, server/lib-ext or the process working directory outside of vendor update windows.
      • Network telemetry (Zeek conn.log / Suricata): outbound connections from the PaperCut host to atypical ports (anything other than 443/389/636/1433/5432/631/9100) or to non-corporate ASNs. KQL shape: DeviceNetworkEvents | where InitiatingProcessFileName in~ ("java.exe","pc-app.exe") and RemotePort !in (443,389,636,1433,5432) | summarize by RemoteIP, RemotePort.
      • PaperCut audit log: admin logins outside business hours and changes to any config key containing „driver", „classpath", „script" or „command" — treat each as a high-severity SIEM alert.

    Detection rules

    No NEOSEC detection rule is available for this vulnerability yet.

    Classification under NIS2 and CRA

    Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

    NIS2

    NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

    Read in glossary
    Actively exploited: treat the vulnerability as a priority in vulnerability handling under Art. 21(2)(e) NIS2. If it is exploited in your environment, check the reporting obligation under Art. 23 (early warning within 24 hours).
    CRA

    The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

    Read in glossary
    Since 11.09.2026, manufacturers of affected products with digital elements must report actively exploited vulnerabilities under Art. 14 CRA, with an early warning within 24 hours via ENISA's single reporting platform.
    ISO/IEC 27001

    ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

    Read in glossary
    Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

    Description

    An unsafe dynamic class loading vulnerability exists in the database connection utilities of PaperCut MF and PaperCut NG. The application instantiates database driver classes based on configurable driver names without validating against an allowlist of approved drivers. If an attacker can manipulate system configuration parameters, this enables the execution of arbitrary Java bytecode residing on the application classpath under the security context of the PaperCut server process.

    Source: cvelistv5, NVD (NIST), CISA KEV Catalog

    Affected products

    The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

    Affected products
    Affected versionsFixed in
    PaperCutPaperCut MF/NG
    • 25.0.0 – < 25.0.13
    • 26.0.0 – < 26.0.5
    • < 24.1.10
    • 25.0.13
    • 26.0.5
    • 24.1.10
    papercutpapercut_mf
    • 25.0.2 – < 25.0.12
    • < 24.1.9
    • 26.0.2 – < 26.0.4
    • 25.0.12
    • 24.1.9
    • 26.0.4
    papercutpapercut_ng
    • 26.0.2 – < 26.0.4
    • < 24.1.9
    • 25.0.2 – < 25.0.12
    • 26.0.4
    • 24.1.9
    • 25.0.12

    Vendors and products

    Weakness classes (CWE)

    • CWE-470Use of Externally-Controlled Input to Select Classes or Code ('Unsafe Reflection')

      Base

      The product uses external input with reflection to select which classes or code to use, but it does not sufficiently prevent the input from selecting improper classes or code.

      Entry at MITRE CWE-470

    Public exploit references

    Publicly reported proof-of-concepts, exploit modules and detection templates for this vulnerability. NEOSEC links to the original sources only and does not provide any exploit code.

    Public exploit references
    CISA KEV CatalogCISA Known Exploited Vulnerability (opens in a new tab)cisa.govactively exploited
    Metasploit Framework (Pull Request)Metasploit PR #21842 (opens in a new tab)github.comPoC (publicly reported)reported, not verified—

    References & sources

    • papercut.comkb/Main/security-bulletin-27-aug-2026-urgent-security-advisory
    • github.comrapid7/metasploit-framework/pull/21842Exploit
    • cisa.govCISA KEVgovernment-resource

    Changes to this CVE

    Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).

    1. Record modifiedeb41dac7…

      1 individual change: Affected versions (publisher)

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Affected versions (publisher)added
      —
      Affected value modified. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/82xxx/CVE-2026-82078.json">CVE-2026-82078</a>

      Source identifier: eb41dac7-0af8-4f84-9f6d-0272772514f4

    2. Record modifiedCISA ADP

      CISA assessment (SSVC): exploitation: active, automatable: no

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      SSVC assessmentchanged
      {"id":"CVE-2026-82078","role":"CISA Coordinator","options":[{"exploitation":"active"},{"automatable":"no"},{"technicalImpact":"total"}],"version":"2.0.3","timestamp":"2026-08-31T15:25:19.545218Z"}
      {"id":"CVE-2026-82078","role":"CISA Coordinator","options":[{"exploitation":"active"},{"automatable":"no"},{"technicalImpact":"total"}],"version":"2.0.3","timestamp":"2026-08-28T00:00:00+00:00"}

      Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

    3. Initial analysis by NVDNVD

      Newly listed as affected:
      • PaperCut MF (before 24.1.9; 25.0.2 – before 25.0.12; 26.0.2 – before 26.0.4)
      • PaperCut NG (before 24.1.9; 25.0.2 – before 25.0.12; 26.0.2 – before 26.0.4)

      CVSS V3.1: AV:N/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H

      Show 5 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      CVSSadded
      —
      AV:N/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H
      Product configurationadded
      —
      OR *cpe:2.3:a:papercut:papercut_mf:*:*:*:*:*:*:*:* versions up to (excluding) 24.1.9 *cpe:2.3:a:papercut:papercut_ng:*:*:*:*:*:*:*:* versions up to (excluding) 24.1.9 *cpe:2.3:a:papercut:papercut_mf:*:*:*:*:*:*:*:* versions from (including) 25.0.2 up to (excluding) 25.0.12 *cpe:2.3:a:papercut:papercut_mf:*:*:*:*:*:*:*:* versions from (including) 26.0.2 up to (excluding) 26.0.4 *cpe:2.3:a:papercut:papercut_ng:*:*:*:*:*:*:*:* versions from (including) 25.0.2 up to (excluding) 25.0.12 *cpe:2.3:a:papercut:papercut_ng:*:*:*:*:*:*:*:* versions from (including) 26.0.2 up to (excluding) 26.0.4
      Reference typeadded
      —
      PaperCut: https://www.papercut.com/kb/Main/security-bulletin-27-aug-2026-urgent-security-advisory/ Types: Patch, Vendor Advisory
      Reference typeadded
      —
      CISA-ADP: https://github.com/rapid7/metasploit-framework/pull/21842 Types: Issue Tracking, Patch
      Reference typeadded
      —
      CISA-ADP: https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-82078 Types: Patch, Third Party Advisory, US Government Resource

      Source identifier: nvd@nist.gov

    4. Record modifiedCISA ADP

      CISA assessment (SSVC): exploitation: active, automatable: no

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      SSVC assessmentchanged
      {"id":"CVE-2026-82078","role":"CISA Coordinator","options":[{"exploitation":"poc"},{"automatable":"no"},{"technicalImpact":"total"}],"version":"2.0.3","timestamp":"2026-08-31T12:33:45.803363Z"}
      {"id":"CVE-2026-82078","role":"CISA Coordinator","options":[{"exploitation":"active"},{"automatable":"no"},{"technicalImpact":"total"}],"version":"2.0.3","timestamp":"2026-08-31T15:25:19.545218Z"}

      Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

    5. CISA KEV entry updated9119a7d8…

      4 individual changes: Date Added, Due Date, Required Action, Vulnerability Name

      Show 4 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Date Addedadded
      —
      2026-08-31
      Due Dateadded
      —
      2026-08-31
      Required Actionadded
      —
      2026-08-31
      Vulnerability Nameadded
      —
      2026-08-31

      Source identifier: 9119a7d8-5eab-497f-8521-727c672e3725

    Show 4 older changes

    1. Record modifiedCISA ADP

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-82078

      Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

    2. Record modifiedCISA ADP

      CISA assessment (SSVC): exploitation: proof of concept, automatable: no

      Show 2 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      https://github.com/rapid7/metasploit-framework/pull/21842
      SSVC assessmentchanged
      {"id":"CVE-2026-82078","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"no"},{"technicalImpact":"total"}],"version":"2.0.3","timestamp":"2026-08-28T00:00:00+00:00"}
      {"id":"CVE-2026-82078","role":"CISA Coordinator","options":[{"exploitation":"poc"},{"automatable":"no"},{"technicalImpact":"total"}],"version":"2.0.3","timestamp":"2026-08-31T12:33:45.803363Z"}

      Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

    3. Record modifiedCISA ADP

      CISA assessment (SSVC): exploitation: none known, automatable: no

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      SSVC assessmentchanged
      {"id":"CVE-2026-82078","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"no"},{"technicalImpact":"total"}],"version":"2.0.3","timestamp":"2026-08-28T15:35:13.512853Z"}
      {"id":"CVE-2026-82078","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"no"},{"technicalImpact":"total"}],"version":"2.0.3","timestamp":"2026-08-28T00:00:00+00:00"}

      Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

    4. Receivedeb41dac7…

      CVSS V4.0: AV:N/AC:L/AT:N/PR:H/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H

      Weakness type: CWE-470

      Description added or changed

      Show 5 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Descriptionadded
      —
      An unsafe dynamic class loading vulnerability exists in the database connection utilities of PaperCut MF and PaperCut NG. The application instantiates database driver classes based on configurable driver names without validating against an allowlist of approved drivers. If an attacker can manipulate system configuration parameters, this enables the execution of arbitrary Java bytecode residing on the application classpath under the security context of the PaperCut server process.
      CVSSadded
      —
      AV:N/AC:L/AT:N/PR:H/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H/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
      Weakness type (CWE)added
      —
      CWE-470
      Affected versions (publisher)added
      —
      New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/82xxx/CVE-2026-82078.json">CVE-2026-82078</a>
      Referenceadded
      —
      https://www.papercut.com/kb/Main/security-bulletin-27-aug-2026-urgent-security-advisory/

      Source identifier: eb41dac7-0af8-4f84-9f6d-0272772514f4

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