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Cybersecurity: Threats and Defences
12OCT

PaperCut print servers under active attack

2 min read
10:55UTC

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 incidents⁠1. 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 environments⁠2.

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 organisations⁠3, 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.
Different Perspectives
ENISA
ENISA
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LKA Hamburg
LKA Hamburg
Hamburg's State Criminal Police Office led the operation that took the KillSec leak site on 30 September, with ten countries, Europol and Eurojust. Investigators link the group to around 1,000 suspected attacks, at least 70 in Germany, and the seizure blocks access to at least 110 terabytes of victims' data.
ASOS
ASOS
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Check Point
Check Point
Check Point updated its advisory on 20 September to say its 9.8-rated VPN certificate flaw had been exploited on Spark firewalls since 12 September, five days after the advisory first appeared, and shipped fixes including R81.20 Take 166. It told customers using only pre-shared-key VPN communities they were not exposed.
Japan's National Police Agency
Japan's National Police Agency
Japan's National Police Agency and National Cybersecurity Office signed advisory AA26-281A and published it on 9 October, naming SoftEther VPN, MicroScan and office-cli and indicators detected since January 2016. Tokyo says the evidence comes from several FBI criminal investigations and that it will deepen cooperation with allies.
CISA
CISA
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