Background exploitation KEV catalog Ransomware No authentication

CVE-2023-27351

PaperCut NG/MF Improper Authentication Vulnerability

CheckOps priority index

8.6/10 Patch within 24 h

Severity8.2

Probability7.8

Exploitation5/5

Severity = CVSS. Probability = EPSS (FIRST). Exploitation = public signals: KEV, EUVD, ransomware, EPSS above 10 %, no account required.

EPSS · today 78.1% higher than 99.6% of CVEs

CVSS 3.0 8.2 AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:

Exploited for 197 days 20 Apr 2026

CISA due date 04 May 2026 for US federal agencies

Exploitation probability EPSS · FIRST

EPSS probability (%)Percentile among all CVEs

Exploitation signals 5 / 5

KEV catalog (CISA)20 Apr 2026
Exploited in EUVD (ENISA)20 Apr 2026
Used by ransomwareyes
EPSS above 10 %78.1%
No account, over the networkyes

What to do

Fix

Apply the vendor’s fix as soon as it is available.

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

Meanwhile

Take the service off the internet or restrict access to it, watch the logs and look for signs of compromise.

Manufacturers (CRA)

Exploited vulnerability in your product: early warning to ENISA within 24 h, then notification within 72 h (Article 14 of the Cyber Resilience Act). The CRA explained

Description ENISA EUVD

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

NGNG/MF

Affected versions

22.0.5 (Build 63914)

Weaknesses (CWE)

CWE-287

Open source packages OSV

Affected libraries according to OSV, with fixed versions.

Timeline

20 Apr 2023
Published
20 Apr 2026
Exploitation reported (ENISA)
20 Apr 2026
Added to the KEV catalog
04 May 2026
CISA remediation due date
26 Sept 2026
EPSS peak: 78.1%

References

Other exploited vulnerabilities from the same vendor

CVE-2026-82078PaperCut NG/MF Unsafe Reflection Vulnerability
7.5 · Actively exploited
CVE-2026-81578PaperCut NG/MF Missing Authentication for Critical Function Vulnerability
8.5 · Actively exploited
CVE-2023-2533PaperCut NG/MF Cross-Site Request Forgery (CSRF) Vulnerability
6.0 · Background exploitation
CVE-2023-27350PaperCut MF/NG Improper Access Control Vulnerability
9.9 · Background exploitation