PaperCut NG/MF Missing Authentication for Critical Function
CVE-2026-81578 is a critical-severity authentication bypass by primary weakness vulnerability in PaperCut MF/NG from PaperCut, with a CVSS 3.1 base score of 9.8 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists versions 24.1.10, 25.0.13, 26.0.5 as the first without the flaw, so updating PaperCut MF/NG to one of those releases or later removes the exposure. CISA added it to the Known Exploited Vulnerabilities catalogue on August 31, 2026, which means attacks have been observed in the wild.
Attackers are already exploiting this vulnerability, according to CISA.
What to do
- Update PaperCut MF/NG to 24.1.10 or 25.0.13 or 26.0.5, whichever matches your release line, or a later version.
- Update Papercut Mf to 24.1.9 or 25.0.12 or 26.0.4, whichever matches your release line, or a later version.
- Update Papercut Ng to 24.1.9 or 25.0.12 or 26.0.4, whichever matches your release line, or a later version.
- CISA's 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.
- Read the advisory on papercut.com for workarounds and exact fixed builds.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| PaperCut | PaperCut MF/NG | before 24.1.10; 25.0.0 up to, but not including, 25.0.13; 26.0.0 up to, but not including, 26.0.5 | 24.1.10, 25.0.13, 26.0.5 |
| Papercut | Papercut Mf | before 24.1.9; 25.0.2 up to, but not including, 25.0.12; 26.0.2 up to, but not including, 26.0.4 | 24.1.9, 25.0.12, 26.0.4 |
| Papercut | Papercut Ng | before 24.1.9; 25.0.2 up to, but not including, 25.0.12; 26.0.2 up to, but not including, 26.0.4 | 24.1.9, 25.0.12, 26.0.4 |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 4.0 | 8.8 | High | CNA |
| CVSS 3.1 | 9.8 | Critical | NVD |
Official 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.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: 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.
More Authentication Bypass by Primary Weakness vulnerabilities (CWE-305)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: active, automatable: yes, technical impact: partial).
- Added to CISA's Known Exploited Vulnerabilities catalogue.
- Record last changed materially (score, affected products, status or references).
- Deadline for US federal agencies to remediate, set by CISA.
References
Patches and release notes
- github.com/rapid7/metasploit-framework/pull/21842Issue Tracking
- cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-81578Third Party Advisory, US Government Resource
Our coverage
Other vulnerabilities in PaperCut MF/NG
- 9.1 Critical severity
PaperCut NG/MF Unsafe Reflection Exploited
Recent Authentication Bypass by Primary Weakness vulnerabilities
- 9.3 Critical severity
- 7.6 High severity
- 8.8 High severity
- 7.5 High severity
- 9.0 Critical severity
- 8.8 High severity
Spotted an error? Tell us.