CVE-2026-81578: PaperCut NG/MF

Should you act?

Exploited: patch now if you run it

CISA has confirmed exploitation in the wild. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

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.

CISA’s summary

PaperCut NG/MF contains a missing authentication for critical function vulnerability which allows an unauthenticated remote attacker to modify certain system configurations. This vulnerability can be chained with CVE-2026-82078.

Weakness type: CWE-305, CWE-306.

Product: PaperCut NG/MF · Assigned by: PaperCut · Published: 2026-08-28

Affected and fixed versions

Vendor	Product	Affected versions (per CVE record)
PaperCut	PaperCut MF/NG	< 24.1.10, 25.0.0 < 25.0.13, 26.0.0 < 26.0.5

Severity scores

Scored by	CVSS	Score	Vector
PaperCut	4.0	8.8 High	`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`

Attack vector: network (remotely reachable)
Attack complexity: low
Attack requirements: none
Privileges required: none (no login)
User interaction: none

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

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.

Timeline

2026-08-27 — erroneo.us brief: PaperCut NG/MF: Mass-Exploited Pre-Auth RCE Chain (KEV)
2026-08-28 — CVE record published by PaperCut
2026-08-31 — Added to CISA’s Known Exploited Vulnerabilities catalog
2026-09-13 — CVE record last updated
2026-09-14 — CISA remediation deadline for US federal agencies

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Other references from the CVE record and advisory

github.com github.com

All exploited PaperCut vulnerabilities · Today’s Security Digest