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CVE-2023-27351

This vulnerability allows remote attackers to bypass authentication on affected installations of PaperCut NG 22.0.5 (Build 63914).

High Known exploited
Severity
7.5 / 10
High · CVSS 3.1
Exploit chance (EPSS)
78.05%
Chance of exploitation in the next 30 days. Higher than 99.58% of scored vulnerabilities.
Known exploited
Yes
In CISA's catalog since Apr 20, 2026
Weakness
CWE-287 Improper Authentication
Fix
None yet
No fixed version published
Exploited in the wild. PaperCut NG/MF Improper Authentication Vulnerability (PaperCut NG/MF). 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. Due for U.S. federal agencies by May 4, 2026. Known to be used in ransomware campaigns.

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.

How to fix

No fixed version has been published yet. Until one is, remove or replace the package, or turn off or isolate the affected feature. This page updates when a fix ships.

Severity breakdown

CVSS 3.1 7.5

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
None

Weakness

CWE-287: 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 to prevent it
  • Architecture and Design: Use an authentication framework or library such as the OWASP ESAPI Authentication feature.

References

Advisories

Other links

Timeline

  1. Published
  2. Added to CISA's Known Exploited Vulnerabilities catalog
  3. Remediation due for U.S. federal agencies
  4. Last updated by the source
  5. Latest EPSS score
AdvisorySeverityWhy it's related
GHSA-f9x3-7vq9-cph6
Laravel TokenGuard authentication bypass through non-string API credentials
Critical Same weakness, CWE-287
GHSA-r4xp-prcw-77qf
better-auth: OAuth Proxy lets an attacker sign in as another user
Critical Same weakness, CWE-287
GHSA-965c-763c-88jm
better-auth: OAuth state can be used as a Magic Link to sign in as another user
Critical Same weakness, CWE-287
GO-2026-6773
Nginx UI: Casdoor SSO callback uses a constant `state` parameter (login CSRF)
High Same weakness, CWE-287
GO-2026-6786
Nginx UI: TOTP / passkey enrolment requires no re-authentication, enabling persistent account takeover
High Same weakness, CWE-287
GHSA-xv7q-fvmc-jx96
Vikunja: OIDC email-fallback account linking ignores email_verified, enabling local-account takeover
High Same weakness, CWE-287
GHSA-68w4-83fh-f2w8
pyload-ng: getUserData/get_userdata exposed at Perms.ANY allow any authenticated account to brute-force the administrator password
High Same weakness, CWE-287
GHSA-r44w-v6gf-x3p6
pyLoad has an authentication bypass in API key validation (check_apikey cache)
High Same weakness, CWE-287
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