CriticalCVE-2023-2533

    PaperCut MF/NG 22.0.10 (Build 65996 2023-03-27) - Remote code execution via CSRF (CVE-2023-2533)

    Published In CISA KEV since Sources: pwn.watch, CVE.org

    What is affected, what to do

    A Cross-Site Request Forgery (CSRF) vulnerability has been identified in PaperCut NG/MF, which, under specific conditions, could potentially enable an attacker to alter security settings or execute arbitrary code. This could be exploited if the target is an admin with a current login session.

    The vulnerability is being actively exploited; treat it as a priority. Update PaperCut NG/MF to version 2.1.1. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • PaperCut NG/MF lt 22.0.10..2.1.1
    Fixed in
    • PaperCut NG/MF 2.1.1

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

    Metrics

    8.8

    Priority

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

    Source: NVD, CVSS v3

    8.4

    CVSS v3

    Severity High on the scale from 0 to 10.

    Source: pwn.watch, CVE.org

    28.8 %

    EPSS score

    Elevated — model estimates 10-50% exploitation likelihood.

    Source: FIRST EPSS, percentile 98.1

    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
    221.96 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 exploited
    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
    8.8 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
    8.4
    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“.

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    28.8 %
    Elevated — model estimates 10-50% exploitation likelihood.
    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
    98.1
    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-352

    Response and mitigation

    Why act now?

    Prioritisation rationale

    PaperCut servers are a proven target after earlier campaigns against the same product line, because they typically run with high privileges, integrate with AD and are common in education, public-sector and manufacturing networks. This flaw is network-triggerable without authentication but needs a logged-in admin to click a crafted link. That makes it a natural fit for targeted phishing of IT staff, and abuse of scripting settings can turn it into code execution. Exploitation likelihood is very high, and CISA does not flag known ransomware use. If the admin UI is reachable from user networks or the internet, patch as critical within 72 hours. Where admin access is strictly segmented and done from a PAW, an accelerated regular patch cycle is defensible.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Patch: Upgrade PaperCut NG/MF to a fixed build. The context lists fixed versions 20.1.8, 21.2.12 and 22.1.1. One entry in the context is malformed („22.0.10 … 2.1.1“), so confirm the target version in the PaperCut vendor advisory. Prefer the current supported release line over the bare minimum.
      • Inventory: Find every PaperCut NG/MF application server and site server, e.g. by scanning for the default ports TCP 9191/9192 or querying software inventory. Check the version under Admin UI → „About“, and include forgotten test and lab instances.
      • Kill admin sessions: Log out all active admin sessions. Until patched, tell admins not to browse or open email links while logged into the PaperCut admin UI. Exploitation requires a live admin session plus a click by that admin.
      • Audit configuration: In the Config Editor, compare security-relevant settings against your baseline. This covers print and device scripting, sandbox flags (print.script.sandboxed), external auth, admin accounts and API tokens. Any unexplained change means you treat the server as compromised.
      • Rotate credentials if suspicious: Rotate the built-in admin password, the web-services/API tokens and the LDAP/AD sync service account credentials.

    2. Runbook step 2

      Mitigation layers

      • Network segmentation: Expose the admin UI (TCP 9191/9192, paths /admin and /app) only to a dedicated admin VLAN or jump hosts. It should never be internet-facing. Permit client, printer and release-station traffic separately.
      • Reverse proxy / WAF: Drop state-changing admin requests (POST or /app?service=direct/...) whose Origin or Referer header does not match your PaperCut FQDN. This is a standard anti-CSRF control that can be implemented in nginx, HAProxy or a WAF.
      • Application hardening: Disable print and device scripting if unused. Otherwise enforce print.script.sandboxed=Y. Keep admin session timeouts short. Enable the admin-access IP allowlist in PaperCut's security settings if your version supports it.
      • Workstation and identity: Administer PaperCut only from a separate hardened browser profile or a PAW with no email or general browsing. Apply least privilege to PaperCut admin rights, with few full admins and delegated roles for helpdesk tasks.
      • Server endpoint hardening: Run the service under a non-privileged account. Use EDR or AppLocker/WDAC to block pc-app.exe or the PaperCut Java process from spawning shells. Restrict server egress to required destinations (AD, mail, updates).

    3. Runbook step 3

      Detection rules

      • Process ancestry (Sysmon EID 1 / EDR): Watch for pc-app.exe or pc-app-service.exe spawning cmd.exe, powershell.exe, rundll32.exe, certutil.exe or bitsadmin.exe. KQL: DeviceProcessEvents | where InitiatingProcessFileName in~ ("pc-app.exe","pc-app-service.exe") | where FileName in~ ("cmd.exe","powershell.exe","pwsh.exe","rundll32.exe","certutil.exe"). On Linux, use auditd execve events where the parent is java running as the papercut user (/bin/sh, bash, curl, wget).
      • PaperCut application log: Search the application log or server/logs/server.log for Config Editor changes to print-and-device.script.enabled, print.script.sandboxed or auth and security keys. Also look for newly added admins or modified printer scripts. Alert on any such change without a matching change ticket.
      • Proxy/web logs: Look for admin requests to /app or /admin carrying a foreign Referer that coincide with an admin clicking an email or web link. Sigma shape: cs-uri-stem|startswith: '/app' AND cs-referer|re: '^https?://(?!papercut\.corp\.example)'.
      • Network telemetry (Zeek/Suricata): Flag new outbound connections or executable downloads from the PaperCut server. Also flag connections to TCP 9191/9192 from outside the admin zone.
      • Persistence (Windows EID 4698/4720/7045): Watch for new scheduled tasks, local accounts or services on the PaperCut host shortly after configuration changes.

    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

    A Cross-Site Request Forgery (CSRF) vulnerability has been identified in PaperCut NG/MF, which, under specific conditions, could potentially enable an attacker to alter security settings or execute arbitrary code. This could be exploited if the target is an admin with a current login session. Exploiting this would typically involve the possibility of deceiving an admin into clicking a specially crafted malicious link, potentially leading to unauthorized changes.

    Source: pwn.watch, NVD (NIST), cvelistv5, CISA KEV Catalog, CVE.org (MITRE)

    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 NG/MF
    • 22.0.10 – < 2.1.1
    • 2.1.1
    papercutpapercut_mf
    • 21.0.0 – < 21.2.12
    • < 20.1.8
    • 22.0.0 – < 22.1.1
    • 21.2.12
    • 20.1.8
    • 22.1.1
    papercutpapercut_ng
    • 21.0.0 – < 21.2.12
    • 22.0.0 – ≤ 22.1.1
    • < 20.1.8
    • 21.2.12
    • —
    • 20.1.8

    Vendors and products

    Weakness classes (CWE)

    • CWE-352Cross-Site Request Forgery (CSRF)

      Compound

      The web application does not, or cannot, sufficiently verify whether a request was intentionally provided by the user who sent the request, which could have originated from an unauthorized actor.

      Entry at MITRE CWE-352

    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

    References & sources

    • fluidattacks.comadvisories/arcangelExploit, Third-party advisory
    • papercut.comPaperCut advisory: PaperCut NG/MFVendor advisory, pwn-watch
    • cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2023-2533government-resource, US government resource
    • pwn.watchpwn.watch: PaperCut NG/MF: NG/MF Cross-Site Request Forgery (CSRF) Vulnerabilitypwn-watch
    • NVD (NIST)NVD: CVE-2023-2533pwn-watch
    • cisa.govCISA Known Exploited Vulnerabilities Catalogpwn-watch
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