CVE-2026-81578

PaperCut NG/MF Missing Authentication for Critical Function Vulnerability

Actively exploited (CISA KEV) Critical 9.8 CVSS 3.1

Description

An improper access control vulnerability exists in the web management interface of PaperCut MF and PaperCut NG. Under specific conditions, unauthenticated remote requests targeting administrative functions can trigger backend actions prior to the completion of access validation checks. This allows an unauthenticated remote attacker to modify certain system configurations.

Description as published by the source, in English.

Key facts

Published: 2026-08-28
Last modified: 2026-09-14
Assigned by: eb41dac7-0af8-4f84-9f6d-0272772514f4
CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Scored by: nvd@nist.gov (NVD Primary)
Fix available: Yes, see references

Actively exploited

CISA added this vulnerability to the Known Exploited Vulnerabilities catalogue on 2026-08-31, with a remediation deadline of 2026-09-14 for US federal agencies.

Required action: Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.

Affected products

Vendor	Product	Versions	Status
Papercut	Papercut Mf	< 24.1.9	Affected
Papercut	Papercut Mf	≥ 25.0.2, < 25.0.12	Affected
Papercut	Papercut Mf	≥ 26.0.2, < 26.0.4	Affected
Papercut	Papercut Ng	< 24.1.9	Affected
Papercut	Papercut Ng	≥ 25.0.2, < 25.0.12	Affected
Papercut	Papercut Ng	≥ 26.0.2, < 26.0.4	Affected

Weakness type

CWE-306: Missing Authentication for Critical Function
The product does not perform any authentication for functionality that requires a provable user identity or consumes a significant amount of resources.
CWE-305: Authentication Bypass by Primary Weakness
The authentication algorithm is sound, but the implemented mechanism can be bypassed as the result of a separate weakness that is primary to the authentication error.

References

https://www.papercut.com/kb/Main/security-bulletin-27-aug-2026-urgent-security-advisory/ Patch, Vendor Advisory
https://github.com/rapid7/metasploit-framework/pull/21842 Issue Tracking, Patch
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-81578 Patch, Third Party Advisory, US Government Resource

Related at Berigo

Articles

The vendor confirms ongoing attacks against every version of PaperCut Same product 2026-09-01
PaperCut confirms that a vulnerability present in every release of PaperCut NG and MF is being exploited. Emergency patches for versions 25 and 26 ar…

Does this affect you?

A vulnerability matters only if you run the product, in an affected version, somewhere an attacker can reach.

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Sources and freshness

CVE

What it is: A reference number naming one specific vulnerability, for example CVE-2024-9474.
What it tells you: Which vulnerability we are talking about, and in which product.
What it does NOT tell you: Nothing about how serious it is, whether anyone is exploiting it, or whether it concerns you.
Why it matters: Without a shared number, vendor, authority and tooling cannot discuss the same flaw.
Used with the others: The number is the key. NVD, KEV and EPSS all describe the same CVE.

NVD CWE CISA KEV EPSS

How to read this together

No single value should be used on its own. A high CVSS score does not mean a vulnerability is being exploited, and a low one does not mean it is harmless. The four sources answer four different questions.

CVE names the specific vulnerability.
NVD adds severity and technical detail about it.
CWE describes the type of mistake behind it.
CISA KEV shows that it is already being exploited.
EPSS estimates how likely exploitation is soon.

The order that decides what is urgent

Do you actually have the product?
Is the version you run affected?
Is it listed in CISA KEV?
Does it have a high EPSS score?
Is the system reachable from the internet or from others?
How important is the system to the business?
Are there compensating controls already in place?

The first two questions are not about the vulnerability at all. They are about you, and they remove most of the list before you start.

A short example

Fix this week

CVSS 6,5 (medium)

In CISA KEV: yes
EPSS: 94 per cent
A firewall facing the internet

Can be scheduled

CVSS 9,8 (critical)

In CISA KEV: no
EPSS: 0,04 per cent
A test server with no internet access

Sorted by CVSS alone, the one on the right comes first. It is the more serious flaw in theory. But the one on the left is being used against real organisations right now, and it sits where an attacker can reach it. That is the one to fix first.

The critical one still has to be fixed. It just does not have to be fixed today.

This product uses the NVD API but is not endorsed or certified by the NVD. CVE and the CVE logo are registered trademarks of The MITRE Corporation; CVE records are used under the CVE Terms of Use. CWE is a trademark of The MITRE Corporation, used per the CWE Terms of Use. KEV data from CISA (CC0). Exploitation probability from EPSS, a FIRST.org project. Open-source package data from OSV and the GitHub Advisory Database (CC-BY 4.0).

Scores and vectors are shown as published by the sources. The ordering of results is Berigo's own editorial assessment, described on the search page, and is not NVD data. An empty result never means a system is safe.