PaperCut NG/MF Improper Authentication Vulnerability (CVE-2023-27351)

PaperCut NG/MF contains an improper authentication vulnerability that could allow remote attackers to bypass authentication on affected installations via the SecurityRequestFilter class.

Published Apr 20, 2023 · Updated May 29, 2026

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Why patchRisk explained in plain English

Worst-case scenarioIf unpatched

A remote attacker, without authentication, can achieve full data confidentiality loss. CISA has confirmed use of this vulnerability in known ransomware campaigns — treat as high priority for remediation. Federal agencies are required to remediate by 2026-05-04 under CISA BOD 22-01.

How the attack worksNo clicks needed

This is a Improper Authentication (CWE-287) vulnerability in PaperCut NG/MF. 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. Exploitation requires remote network access, low attack complexity, no authentication required, and no user interaction required.

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Phishing link

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Malicious file

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Server compromised

Am I affected?Quick check

Probably yes if any of these apply:

●IT Security

●Running papercut mf: 15.0 ≤ v < 20.1.7, 21.0.0 ≤ v < 21.2.11, 22.0.0 ≤ v < 22.0.9; papercut ng: 15.0 ≤ v < 20.1.7, 21.0.0 ≤ v < 21.2.11, 22.0.0 ≤ v < 22.0.9

Real-world incidentsWhat we've seen

CISA confirms this CVE has been used in known ransomware campaigns. Added to the KEV catalog on 2026-04-20; federal agencies required to remediate by 2026-05-04.

How to patch

Manual remediation steps

Apply the Vendor Patch

This vulnerability is in the CISA Known Exploited Vulnerabilities catalog — apply the vendor's security update as soon as possible.

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.