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

High severity, CVSS 7.5. Actively exploited: in CISA KEV since 2026-04-20. EPSS: 78.1% chance of exploitation in the next 30 days.

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.

Affected products

• PaperCut PaperCut MF: from 15.0, before 20.1.7 (fixed in 20.1.7); from 21.0.0, before 21.2.11 (fixed in 21.2.11); from 22.0.0, before 22.0.9 (fixed in 22.0.9)
• PaperCut PaperCut NG: from 15.0, before 20.1.7 (fixed in 20.1.7); from 21.0.0, before 21.2.11 (fixed in 21.2.11); from 22.0.0, before 22.0.9 (fixed in 22.0.9)

Published 2023-04-20. Last modified 2026-10-01.