CVE-2023-27351: PaperCut NG/MF Improper Authentication Vulnerability

In short

PaperCut NG/MF has a weakness classified as improper authentication (CWE-287). CISA added it to its Known Exploited Vulnerabilities catalog on 2026-04-20. NVD lists CVSS 3.1 at 7.5 HIGH. CISA reports known ransomware campaign use.

What it is

“PaperCut NG/MF contains an improper authentication vulnerability that could allow remote attackers to bypass authentication on affected installations via the SecurityRequestFilter class.” — CISA KEV, retrieved 2026-11-01

“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.” — NVD, retrieved 2026-11-01

Who is affected

PaperCut NG/MF. NVD lists the following versions as affected:

• Papercut Papercut Mf: from 15.0 inclusive, before 20.1.7
• Papercut Papercut Mf: from 21.0.0 inclusive, before 21.2.11
• Papercut Papercut Mf: from 22.0.0 inclusive, before 22.0.9
• Papercut Papercut Ng: from 15.0 inclusive, before 20.1.7
• Papercut Papercut Ng: from 21.0.0 inclusive, before 21.2.11
• Papercut Papercut Ng: from 22.0.0 inclusive, before 22.0.9

Exploitation status

CISA KEV added: 2026-04-20. Known ransomware campaign use: Known (reported by CISA). Due date CISA set for US federal civilian agencies: 2026-05-04.

Scores

NVD CVSS 3.1: 7.5 HIGH; vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N; source [email protected].

EPSS by FIRST: 78.05%; percentile 99.58; score date 2026-10-31. EPSS estimates the probability of exploitation in the next 30 days.

CWE: CWE-287.

Timeline

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.” — CISA KEV

What to do

• Confirm whether you run PaperCut NG/MF and which version.
• Apply the vendor update or mitigation in the advisory.
• Follow CISA’s required action.
• Review the vendor guidance on signs of compromise.
• Track the fix through completion.

References

• Vendor Advisory: https://www.papercut.com/kb/Main/PO-1216-and-PO-1219
• Third Party Advisory, VDB Entry: https://www.zerodayinitiative.com/advisories/ZDI-23-232/
• NVD detail
• CVE.org record
• CISA KEV catalog

Sources and dates

CISA Known Exploited Vulnerabilities Catalog, version 2026.10.30; retrieved 2026-11-01. CISA KEV data: CC0 1.0. No endorsement by CISA.

NVD retrieved: 2026-11-01. This product uses the NVD API but is not endorsed or certified by the NVD.

EPSS scores by FIRST; score date 2026-10-31.