Suspicious Java Class File Created in PaperCut Server Library
Detects creation of Java .class files within the PaperCut NG/MF Application Server library directory. During active exploitation of CVE-2026-82078 (chained with CVE-2026-81578), attackers deliver hex-encoded…
Description
Detects creation of Java .class files within the PaperCut NG/MF Application Server library directory. During active exploitation of CVE-2026-82078 (chained with CVE-2026-81578), attackers deliver hex-encoded malicious .class payloads into the PaperCut server/lib path (observed examples include Udydn.class and Moo97.class) so arbitrary bytecode executes inside the PaperCut JVM / Application Server process.
Detection logic
Its licence does not clear it for publishing here
Sunturai publishes a detection's own text where the licence it arrived under has been reviewed and permits it, and Elastic License 2.0 has not. The query as its source wrote it, its canonical form and the hash that pins this revision are in the workspace record.
Detection requirements
- Platform
- ContainersESXiIaaSIdentity ProviderLinuxmacOSNetwork DevicesOffice SuiteSaaSWindows
The rule states no platform. This is derived from the 3 ATT&CK techniques it maps to.
- Log source category
- event_index
MITRE ATT&CK mappings
0 exclusive techniques.This is coverage no other published rule has; it is not this rule's total technique count.
References
| Reference | Cited by |
|---|---|
| www.huntress.com/blog/papercut-actively-exploited | 2 |
| www.papercut.com/kb/Main/security-bulletin-27-aug-2026-urgent-security-advisory/ | 2 |
From the source
- At source
- Open at source
- Upstream identifier
- a2d4508e-e9c2-41f6-9466-0c3aed8cc2c9
- Tagged by the source as
- Data Source: Elastic DefendDomain: EndpointOS: LinuxOS: macOSOS: WindowsPlatform: LinuxPlatform: macOSPlatform: WindowsResources: Investigation GuideRule Type: Event Correlation (EQL)Tactic: Defense EvasionTactic: ExecutionTactic: Initial AccessUse Case: Threat DetectionUse Case: VulnerabilityVuln: CVE-2026-81578Vuln: CVE-2026-82078
Licence
- Published under
- Elastic License 2.0Read the licence
- Attribution
- Required
Authorship
- Written by
- Published
- Sep 20, 2026
- Version
- 2