PaperCut NG Suspicious Behavior Debug Log

name: PaperCut NG Suspicious Behavior Debug Log
id: 395163b8-689b-444b-86c7-9fe9ad624734
version: 7
date: '2026-02-25'
author: Michael Haag, Splunk
status: production
type: Hunting
data_source: []
description: The following analytic identifies potential exploitation attempts on a PaperCut NG server by analyzing its debug log data. It detects unauthorized or suspicious access attempts from public IP addresses and searches for specific URIs associated with known exploits. The detection leverages regex to parse unstructured log data, focusing on admin login activities. This activity is significant as it can indicate an active exploitation attempt on the server. If confirmed malicious, attackers could gain unauthorized access, potentially leading to data breaches or further compromise of the server.
search: |-
    `papercutng`
    (loginType=Admin OR userName=admin)

    | eval uri_match=if(match(_raw, "(?i)(\/app\?service=page\/SetupCompleted|\/app|\/app\?service=page\/PrinterList|\/app\?service=direct\/1\/PrinterList\/selectPrinter&sp=l1001|\/app\?service=direct\/1\/PrinterDetails\/printerOptionsTab\.tab)"), "URI matches", null())

    | eval ip_match=if(match(_raw, "(?i)((25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?))") AND NOT match(_raw, "(?i)(10\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?))|(172\.(1[6-9]|2[0-9]|3[0-1])\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?))|(192\.168\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?))"), "IP matches", null())

    | where  (isnotnull(uri_match) OR isnotnull(ip_match))
    | stats sparkline, count, values(uri_match) AS uri_match, values(ip_match) AS ip_match latest(_raw) BY host, index, sourcetype
    | `papercut_ng_suspicious_behavior_debug_log_filter`
how_to_implement: Debug logs must be enabled and shipped to Splunk in order to properly identify behavior with this analytic.
known_false_positives: False positives may be present, as this is based on the admin user accessing the Papercut NG instance from a public IP address. Filter as needed.
references:
    - https://www.papercut.com/kb/Main/HowToCollectApplicationServerDebugLogs
    - https://github.com/inodee/threathunting-spl/blob/master/hunt-queries/HAFNIUM.md
    - https://www.cisa.gov/news-events/alerts/2023/05/11/cisa-and-fbi-release-joint-advisory-response-active-exploitation-papercut-vulnerability
    - https://www.papercut.com/kb/Main/PO-1216-and-PO-1219
    - https://www.horizon3.ai/papercut-cve-2023-27350-deep-dive-and-indicators-of-compromise/
    - https://www.bleepingcomputer.com/news/security/hackers-actively-exploit-critical-rce-bug-in-papercut-servers/
    - https://www.huntress.com/blog/critical-vulnerabilities-in-papercut-print-management-software
tags:
    analytic_story:
        - PaperCut MF NG Vulnerability
    asset_type: Web Server
    atomic_guid: []
    mitre_attack_id:
        - T1190
        - T1133
    product:
        - Splunk Enterprise
        - Splunk Enterprise Security
        - Splunk Cloud
    security_domain: endpoint
tests:
    - name: True Positive Test
      attack_data:
        - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1190/papercut/server.log
          source: papercutng
          sourcetype: papercutng