PaperCut NG/MF Improper Authentication
CVE-2023-27351 is a high-severity improper authentication vulnerability in NG from PaperCut, with a CVSS 3.1 base score of 7.5 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. Affected NG versions: 22.0.5 (Build 63914). The record does not name a fixed version, so check the vendor advisory. CISA added it to the Known Exploited Vulnerabilities catalogue on April 20, 2026, which means attacks have been observed in the wild, including in ransomware campaigns.
Attackers are already exploiting this vulnerability, according to CISA.
What to do
- Update Papercut Mf to 20.1.7 or 21.2.11 or 22.0.9, whichever matches your release line, or a later version.
- Update Papercut Ng to 20.1.7 or 21.2.11 or 22.0.9, whichever matches your release line, or a later version.
- 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.
- 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 | NG | 22.0.5 (Build 63914) | Not stated |
| Papercut | Papercut Mf | 15.0 up to, but not including, 20.1.7; 21.0.0 up to, but not including, 21.2.11; 22.0.0 up to, but not including, 22.0.9 | 20.1.7, 21.2.11, 22.0.9 |
| Papercut | Papercut Ng | 15.0 up to, but not including, 20.1.7; 21.0.0 up to, but not including, 21.2.11; 22.0.0 up to, but not including, 22.0.9 | 20.1.7, 21.2.11, 22.0.9 |
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
- NoneNothing can be modified.
- Availability
- NoneAvailability is not affected.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 7.5 | High | NVD |
| CVSS 3.0 | 8.2 | High | CNA (trendmicro.com) |
Official description
This vulnerability allows remote attackers to bypass authentication on affected installations of PaperCut NG 22.0.5 (Build 63914). Authentication is not required to exploit this vulnerability. The specific flaw exists within the SecurityRequestFilter class. The issue results from improper implementation of the authentication algorithm. An attacker can leverage this vulnerability to bypass authentication on the system. Was ZDI-CAN-19226.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Improper Authentication
When an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct.
How developers prevent this class of flaw
- Use an authentication framework or library such as the OWASP ESAPI Authentication feature.
Timeline
- CVE record published.
- Added to CISA's Known Exploited Vulnerabilities catalogue.
- CISA published its SSVC assessment (exploitation: active, automatable: yes, technical impact: total).
- Deadline for US federal agencies to remediate, set by CISA.
- Record last changed materially (score, affected products, status or references).
References
Advisories
Third-party and government advisories
- zerodayinitiative.com/advisories/ZDI-23-232/Third Party Advisory, VDB Entry
- cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2023-27351US Government Resource
Other vulnerabilities in NG
- 7.2 High severity
- 7.2 High severity
- 9.8 Critical severity
PaperCut MF/NG Improper Access Control Exploited
Recent Improper Authentication vulnerabilities
- 7.5 High severity
- 8.8 High severity
- 7.1 High severity
- 9.8 Critical severity
- 9.8 Critical severity
- 9.8 Critical severity
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