CVE-2026-81578: PaperCut NG/MF Missing Authentication for Critical Function Vulnerability

Critical severity, CVSS 9.8. Actively exploited: in CISA KEV since 2026-08-31. EPSS: 85.6% chance of exploitation in the next 30 days.

An improper access control vulnerability exists in the web management interface of PaperCut MF and PaperCut NG. Under specific conditions, unauthenticated remote requests targeting administrative functions can trigger backend actions prior to the completion of access validation checks. This allows an unauthenticated remote attacker to modify certain system configurations.

Affected products

• PaperCut PaperCut MF: before 24.1.9 (fixed in 24.1.9); from 25.0.2, before 25.0.12 (fixed in 25.0.12); from 26.0.2, before 26.0.4 (fixed in 26.0.4)
• PaperCut PaperCut NG: before 24.1.9 (fixed in 24.1.9); from 25.0.2, before 25.0.12 (fixed in 25.0.12); from 26.0.2, before 26.0.4 (fixed in 26.0.4)

Published 2026-08-28. Last modified 2026-09-14.