URGENT: PaperCut NG/MF Security Advisory, immediate action required for internet-facing servers

On August 27th, 2026, PaperCut published an urgent security advisory for PaperCut NG and PaperCut MF. PaperCut has confirmed active exploitation of a vulnerability in the software, along with confirmed customer incidents. All versions of PaperCut NG and MF are affected.

Internet-Facing Servers Are The Priority

The advisory applies to every PaperCut NG and MF installation, but the immediate risk is to Application Servers that are accessible from the public internet. Organizations running an internet-facing PaperCut Application Server should treat this as an emergency and act today. Installations reachable only from within an internal network carry lower immediate risk, though the emergency patch should still be applied.

Immediate Action Required

PaperCut's instructions are as follows:

"If your PaperCut NG/MF Application Server is accessible from the public internet, immediately restrict web access to trusted IP addresses only (e.g., internal IP addresses). Use firewall rules, network access controls, or equivalent measures to ensure the PaperCut server's web interfaces cannot be reached from untrusted internet addresses. Take this action now, even if you have not observed suspicious activity."

Emergency Patch

PaperCut released an emergency patch for v25 and v26 on August 27th, 2026. PaperCut notes that this is not an official release and that it is intended for customers with public-facing servers who are unable to take other mitigating action.

PaperCut has stated that builds for v24 are still in progress. No patches are available for versions earlier than v24 at this time. For those installations, restricting access as described above is the mitigation currently available. PaperCut recommends upgrading to the latest version whenever possible.

Review The Full Advisory

PaperCut is updating the advisory as its investigation continues, and it remains the authoritative source. It includes the complete technical details, indicators of compromise, and investigation guidance for IT and security staff. The advisory should be reviewed directly:

https://www.papercut.com/kb/Main/security-bulletin-27-aug-2026-urgent-security-advisory

How Can UBEO Help? 

UBEO is available to help with questions about PaperCut environments, including applying the emergency patch. Contact the UBEO Help Desk at helpdesk@ubeo.com or to call, go to https://info.ubeo.com/customer-portal and choose your region and correct phone number.