CVE-2023-27351

PaperCut NG/MF authentication bypass, confirmed exploited in the wild.

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

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78%chance of exploitation in the next 30 days (EPSS), 99th percentile

20 Apradded to CISA's Known Exploited Vulnerabilities list, 2026

4 Mayfederal remediation deadline, already passed

Passedpast the deadline: patch now

CISA's name for it	PaperCut NG/MF Improper Authentication Vulnerability
Vendor and product	PaperCut · NG/MF
Type	authentication bypass · CWE-287
Exploited	Confirmed by CISA listed 20 April 2026
Likelihood	one of the most likely to be exploited of every vulnerability tracked
Deadline	4 May 2026 · already passed
Used in ransomware	Yes: CISA reports it used in ransomware campaigns
Advisories	www.papercut.com ↗ · nvd.nist.gov ↗

What to do

Three steps, in this order

Step 1

Apply the vendor fix and restart the affected service.

Step 2

Put the login or management interface behind a VPN or allow-list; a bypass makes passwords irrelevant.

Step 3

Rotate credentials and session keys the product holds, and review accounts and configuration changes since the listing date.

CISA's 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.

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Questions

CVE-2023-27351 in short

Is CVE-2023-27351 being exploited?

Yes. CISA added CVE-2023-27351 to its Known Exploited Vulnerabilities catalogue on 20 April 2026, which it does only on evidence of exploitation in the wild.

What is the CISA deadline for CVE-2023-27351?

US federal agencies must remediate it by 4 May 2026. Everyone else should treat that date as the latest safe point to patch an internet-facing system.

How likely is CVE-2023-27351 to be exploited in the next 30 days?

FIRST's Exploit Prediction Scoring System gives it 78%, the 99th percentile of every CVE it scores.

How do I fix CVE-2023-27351?

Apply the vendor fix and restart the affected service. Put the login or management interface behind a VPN or allow-list; a bypass makes passwords irrelevant. Rotate credentials and session keys the product holds, and review accounts and configuration changes since the listing date.

Same vendor

Other PaperCut vulnerabilities being exploited

CVE	Product	Type	Listed
CVE-2026-82078	NG/MF	exploited vulnerability	31 August 2026
CVE-2026-81578	NG/MF	authentication bypass	31 August 2026

Sources: CISA Known Exploited Vulnerabilities catalogue (released 10 November 2026) and FIRST EPSS. Page compiled automatically by SAK T.L.M, the threat-intelligence tool of SAK T.E.C, on 13 November 2026.