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Cybersecurity: Threats and Defences
5SEP

PaperCut print servers under active attack

2 min read
12:09UTC

PaperCut confirmed on 27 August that attackers were chaining two flaws in its print servers to run code without logging in. Huntress reproduced the chain and found it running in two customer environments.

TechnologyAssessed
Key takeaway

Two chained PaperCut flaws give unauthenticated attackers code execution, and the third emergency patch landed on 1 September.

PaperCut confirmed on 27 August that its own response team was investigating active exploitation of PaperCut NG and PaperCut MF, and that it knew of confirmed customer incidents 1. PaperCut is an Australian software vendor whose print management servers sit between office staff and the printers they send jobs to, which in most estates means a server every desktop in the building is configured to talk to.

The chain joins CVE-2026-81578, an authentication bypass scoring 8.8, to CVE-2026-82078, unsafe dynamic class loading scoring 9.4. A CVE, short for Common Vulnerabilities and Exposures, is the industry's shared reference number for a single flaw. The bypass carries an attacker who has never logged in as far as a configuration change, and the configuration change gets the print server to load and run Java bytecode of the attacker's choosing. Huntress, an American managed detection and response firm, reproduced the whole pre-authentication chain on a stock PaperCut NG 25.0.11.75758 server and found it running in two customer environments 2.

Emergency Patch Release 3 landed on 1 September, the third fix in six days, so an organisation that acted on the first bulletin has taken the print estate down three times inside a working week. Exploitation running ahead of a vendor's own fix has form on this beat: Check Point's remote access VPN carried an authentication bypass for roughly a month before June's hotfix reached customers .

NHS England issued its own alert on the flaws for UK health organisations 3, which is the pattern that decides who actually patches. A vendor bulletin reaches customers on a mailing list; a health service alert reaches every trust that has to answer for it.

Deep Analysis

In plain English

PaperCut makes software that offices use to manage and track office printing. Two flaws in that software, when used together, let an attacker take control of the print server without needing a password first. PaperCut says it knows of two customer networks where this has happened. It released a fix on 1 September. If your organisation runs PaperCut NG or MF, the advice is to apply that patch now rather than wait for a wider warning.

Deep Analysis
Root Causes

PaperCut NG and MF run as on-premises print-management servers that many IT teams treat as low-risk plumbing rather than internet-facing infrastructure, which slows patch cadence relative to servers admins actively watch.

The pre-authentication chain only works because remote printing depends on a reachable web console by design, so the same feature that makes the product useful is what exposes it.

What could happen next?
  • Risk

    Unpatched PaperCut NG/MF installs remain exploitable pre-authentication until Emergency Patch Release 3 is applied, and internet-facing print servers are a common blind spot in patch management.

First Reported In

Update #13 · Four privileged platforms under live attack

PaperCut· 5 Sept 2026
Read original
Causes and effects
This Event
PaperCut print servers under active attack
A print server most organisations treat as plumbing turned out to accept attacker-supplied code with no login at all.
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