PaperCut flaws being used in attacks

CISA lists 5 flaws in PaperCut products as being used in attacks, most recently on 31 Aug 2026. 2 have been used in ransomware.

What to do

1. Update every PaperCut product you use.Install the updates PaperCut offers, on every device, and restart when asked. Each flaw below has a fix or clear advice; that’s one of CISA’s conditions for listing it.
2. If someone looks after IT for you, send them this page.Many of these are in equipment you don’t see: routers, firewalls, servers, the office network. Ask them to confirm each one is fixed, or that you don’t use the product.
3. Check anything else in the lookup.Search any app, company or CVE. Not being on CISA’s list doesn’t mean safe: keep updating either way.

Every flaw, newest first

1. Being used in attacksAdded by CISA on 31 Aug 2026
   PaperCut NG/MF
   CVE-2026-82078PaperCut NG/MF Unsafe Reflection Vulnerability
   PaperCut NG/MF contains an unsafe reflection vulnerability that allows an attacker to manipulate system configuration parameters and execute arbitrary Java bytecode residing on the application classpath under the security context of the PaperCut server process. This vulnerability can be chained with CVE-2026-81578.
   CISA’s required actionApply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Read all

   Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.
   CVE recordNVD
2. Being used in attacksAdded by CISA on 31 Aug 2026
   PaperCut NG/MF
   CVE-2026-81578PaperCut NG/MF Missing Authentication for Critical Function Vulnerability
   PaperCut NG/MF contains a missing authentication for critical function vulnerability which allows an unauthenticated remote attacker to modify certain system configurations. This vulnerability can be chained with CVE-2026-82078.
   CISA’s required actionApply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Read all

   Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.
   CVE recordNVD
3. Being used in attacksUsed in ransomwareAdded by CISA on 20 Apr 2026
   PaperCut NG/MF
   CVE-2023-27351PaperCut NG/MF Improper Authentication Vulnerability
   PaperCut NG/MF contains an improper authentication vulnerability that could allow remote attackers to bypass authentication on affected installations via the SecurityRequestFilter class.
   CISA’s required actionApply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
   CVE recordNVD
4. Being used in attacksAdded by CISA on 28 Jul 2025
   PaperCut NG/MF
   CVE-2023-2533PaperCut NG/MF Cross-Site Request Forgery (CSRF) Vulnerability
   PaperCut NG/MF contains a cross-site request forgery (CSRF) vulnerability, which, under specific conditions, could potentially enable an attacker to alter security settings or execute arbitrary code.
   CISA’s required actionApply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
   CVE recordNVD
5. Being used in attacksUsed in ransomwareAdded by CISA on 21 Apr 2023
   PaperCut MF/NG
   CVE-2023-27350PaperCut MF/NG Improper Access Control Vulnerability
   PaperCut MF/NG contains an improper access control vulnerability within the SetupCompleted class that allows authentication bypass and code execution in the context of system.
   CISA’s required actionApply updates per vendor instructions.
   CVE recordNVD

From CISA’s Known Exploited Vulnerabilities catalog, updated 21 Oct 2026 (version 2026.10.21). CISA’s required actions are written for US government agencies. PaperCut on CISA’s site.