---
title: "CVE-2026-81578: PaperCut NG/MF Missing Authentication for Critical Function Vulnerability"
url: https://erroneo.us/security/cve/CVE-2026-81578/
description: "CVE-2026-81578 (PaperCut NG/MF): Exploited in the wild (CISA KEV). An improper access control vulnerability exists in the web management interface of…"
type: vulnerability-record
section: "Security Digest"
date_published: 2026-08-28
date_modified: 2026-10-21
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2026-81578"
kev: true
cvss: 8.8
epss: 0.85581
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2026-81578: PaperCut NG/MF Missing Authentication for Critical Function Vulnerability

**Signal:** Exploited: patch now if you run it. CISA has confirmed exploitation in the wild. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- Yes, if you run PaperCut NG/MF. CISA added this CVE to its Known Exploited Vulnerabilities catalog on 2026-08-31, which means there is reliable evidence of exploitation in the wild. US federal agencies must remediate by 2026-09-14 ; treat that as the outer limit, not the target.
- EPSS 85.6% , percentile 99.7: FIRST’s model estimates a 85.6% chance of exploitation activity in the next 30 days, higher than 99.7% of all scored CVEs (very high). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Editorial verdict: Act now. PaperCut NG/MF: Mass-Exploited Pre-Auth RCE Chain (KEV) — If a PaperCut NG/MF server below 24.1.10, 25.0.13 or 26.0.5 was reachable from the internet after late August, assume it was compromised: upgrade, then hunt and rebuild, because this chain gave unauthenticated attackers SYSTEM and was mass-exploited.

## What it is

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.

## Affected products (CVE record)

- PaperCut PaperCut MF/NG: < 24.1.10, 25.0.0 < 25.0.13, 26.0.0 < 26.0.5

## Severity

- PaperCut CVSS 4.0: 8.8 `CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:H/VA:L/SC:N/SI:N/SA:N`

## Exploitation

- CISA KEV: added 2026-08-31; federal due date 2026-09-14. Known ransomware use: Unknown.
- CISA 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.
- CISA SSVC assessment: exploitation active , automatable yes , technical impact partial .
- FIRST EPSS (model of 2026-10-21): 85.58% probability of exploitation activity in the next 30 days; percentile 99.7.

## Sources

- [Listed in CISA KEV notes (papercut.com)](https://www.papercut.com/kb/Main/security-bulletin-27-aug-2026-urgent-security-advisory/)
- [CVE.org record CVE-2026-81578](https://www.cve.org/CVERecord?id=CVE-2026-81578)
- [NVD entry CVE-2026-81578](https://nvd.nist.gov/vuln/detail/CVE-2026-81578)
- [CISA Known Exploited Vulnerabilities catalog entry](https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-81578)
- [Listed in CISA KEV notes (cisa.gov)](https://www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-based-risk)
- [Listed in CISA KEV notes (cisa.gov)](https://www.cisa.gov/news-events/directives/bod-26-04-implementation-guidance-prioritizing-security-updates-based-risk)
- [github.com](https://github.com/rapid7/metasploit-framework/pull/21842)

---
Source page: https://erroneo.us/security/cve/CVE-2026-81578/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt