Detection rules › Splunk
PaperCut NG Suspicious Behavior Debug Log
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.
MITRE ATT&CK coverage
| Tactic | Techniques |
|---|---|
| Initial Access | T1133 External Remote Services, T1190 Exploit Public-Facing Application |
| Persistence | T1133 External Remote Services |
Rule body splunk
name: PaperCut NG Suspicious Behavior Debug Log
id: 395163b8-689b-444b-86c7-9fe9ad624734
version: 8
creation_date: '2023-05-15'
modification_date: '2026-05-13'
author: Michael Haag, Splunk
status: production
type: Hunting
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.
data_source: []
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
analytic_story:
- PaperCut MF NG Vulnerability
asset_type: Web Server
mitre_attack_id:
- T1190
- T1133
product:
- Splunk Enterprise
- Splunk Enterprise Security
- Splunk Cloud
category: endpoint
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
test_type: unit
Stages and Predicates
Stage 1: search
`papercutng`
(loginType=Admin OR userName=admin)
Stage 2: eval
| 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())
Stage 3: eval
| 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())
Stage 4: where
| where (isnotnull(uri_match) OR isnotnull(ip_match))
Stage 5: stats
| stats sparkline, count, values(uri_match) AS uri_match, values(ip_match) AS ip_match latest(_raw) BY host, index, sourcetype
Stage 6: search
| `papercut_ng_suspicious_behavior_debug_log_filter`
Indicators
Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.
| Field | Kind | Values |
|---|---|---|
ip_match | is_not_null | |
loginType | eq |
|
sourcetype | eq |
|
uri_match | is_not_null | |
userName | eq |
|