Security Digest · Vulnerability record · Known exploited
CVE-2023-27351: PaperCut NG/MF Improper Authentication Vulnerability
Exploited in the wild (CISA KEV). This vulnerability allows remote attackers to bypass authentication on affected installations of PaperCut NG 22.0.5 (Build 63914).
CISA KEV · added 2026-04-20 CVSS 8.2 High EPSS 78.1% · p99.6
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 2026-04-20, which means there is reliable evidence of exploitation in the wild. US federal agencies must remediate by 2026-05-04; treat that as the outer limit, not the target. CISA also lists it as known to be used in ransomware campaigns.
- EPSS 78.1%, percentile 99.6: FIRST’s model estimates a 78.1% chance of exploitation activity in the next 30 days, higher than 99.6% 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.
What it is
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.
CISA’s summary
PaperCut NG/MF contains an improper authentication vulnerability that could allow remote attackers to bypass authentication on affected installations via the SecurityRequestFilter class.
Weakness type: CWE-287.
Product: PaperCut NG/MF · Assigned by: zdi · Published: 2023-04-20
Affected and fixed versions
| Vendor | Product | Affected versions (per CVE record) |
|---|---|---|
| PaperCut | NG | 22.0.5 (Build 63914) |
Severity scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| zdi | 3.0 | 8.2 High | CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N |
- Attack vector: network (remotely reachable)
- Attack complexity: low
- Privileges required: none (no login)
- User interaction: none
- Scope: unchanged
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 2026-04-20; federal due date 2026-05-04. Known ransomware use: Known.
- CISA 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.
- CISA SSVC assessment: exploitation active, automatable yes, technical impact total.
- FIRST EPSS (model of 2026-10-21): 78.05% probability of exploitation activity in the next 30 days; percentile 99.6.
Timeline
- — CVE record published by zdi
- — Added to CISA’s Known Exploited Vulnerabilities catalog
- — CISA remediation deadline for US federal agencies
- — CVE record last updated
Sources and references
Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.
Vendor and project advisories, patches
- Listed in CISA KEV notes (papercut.com) papercut.com
Vulnerability records
- CVE.org record CVE-2023-27351 cve.org
- NVD entry CVE-2023-27351 nvd.nist.gov
Government
Other references from the CVE record and advisory
- zerodayinitiative.com zerodayinitiative.com
All exploited PaperCut vulnerabilities · Today’s Security Digest