PaperCut NG/MF Improper Authentication Vulnerability. Actively exploited: CISA added this vulnerability to its Known Exploited Vulnerabilities catalog on 20/04/2026. Patch affected systems as an emergency. It is known to be used in ransomware campaigns.
| Package | Affected versions | Patched versions |
|---|---|---|
| papercut mf | ≥ 15.0, < 20.1.7≥ 21.0.0, < 21.2.11≥ 22.0.0, < 22.0.9 | 20.1.721.2.1122.0.9 |
| papercut ng | ≥ 15.0, < 20.1.7≥ 21.0.0, < 21.2.11≥ 22.0.0, < 22.0.9 | 20.1.721.2.1122.0.9 |
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.
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