CVE-2023-27351
PaperCut NG/MF Improper Authentication Vulnerability
PaperCut NG/MF
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.
Ransomware groups exploiting CVE-2023-27351
The ransomware group known as Cl0p is a variant of a previously known strain dubbed CryptoMix. It is worth noting that this variant was delivered as the final payload in a phishing campaign in 2019 and was exclusively financially motivated, with attacks carrie
Exploitation is attributed to these groups across their recorded activity. It does not follow that every organisation they listed was reached through CVE-2023-27351 — the source data does not record an entry point per incident.
Exploitation status
CISA Known Exploited Vulnerabilities
Listed by CISA on 20 April 2026. US federal agencies were required to remediate it by 4 May 2026. CISA records this vulnerability as known to be used in ransomware campaigns.
EPSS — exploitation probability
FIRST puts the probability of exploitation activity in the next 30 days at 78.1%, which is higher than 99.6% of all scored vulnerabilities. EPSS is a forecast of activity, not a measure of severity, and it is rescored daily.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Recent listings by these groups
Disclosures from the groups above, newest first.
Frequently asked questions
Is CVE-2023-27351 being exploited by ransomware groups?
Yes. CVE-2023-27351 is recorded as exploited by Clop. Between them these groups account for 854 victim disclosures in this database. CISA also records this vulnerability as used in ransomware campaigns.
What does CVE-2023-27351 affect?
CVE-2023-27351 affects PaperCut NG/MF. 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 severe is CVE-2023-27351?
CVE-2023-27351 is rated HIGH with a CVSS base score of 7.5. EPSS puts the probability of exploitation in the next 30 days at 78.1%, higher than 99.6% of all scored vulnerabilities. It is listed in the CISA Known Exploited Vulnerabilities catalog, with a federal remediation deadline of 4 May 2026.
How should organisations respond to CVE-2023-27351?
Apply the vendor patch for PaperCut NG/MF as the first priority, and treat any internet-facing instance as the most urgent. Because this vulnerability is associated with ransomware activity, also review whether the affected systems were reachable before patching, rather than assuming that patching alone closes the incident.