Detect CVE-2023-27351 - PaperCut NG/MF Improper Authentication Exploitation in Splunk
Detects exploitation attempts targeting CVE-2023-27351, an improper authentication vulnerability (CWE-287) in PaperCut NG/MF print management software. This CISA KEV-listed vulnerability allows unauthenticated attackers to bypass authentication controls, potentially enabling unauthorized access to the PaperCut administration interface and sensitive print management data. Threat actors have actively exploited PaperCut vulnerabilities in the wild for initial access and lateral movement.
MITRE ATT&CK
SPL Detection Query
index=web OR index=iis OR index=proxy sourcetype IN ("iis", "ms:iis:auto", "access_combined", "nginx:plus:kv")
| eval uri_lower=lower(uri_path)
| eval is_papercut_endpoint=if(
match(uri_lower, "/rpc/api/json|/app\?service=|/health-check|/api/health|/app/admin"),
1, 0
)
| where is_papercut_endpoint=1
| eval is_auth_bypass=if(
match(uri_lower, "/rpc/api/json") AND method="POST" AND status=200
AND NOT match(src_user, "admin|papercut|svc_"),
1, 0
)
| eval is_admin_access=if(
match(uri_lower, "/app") AND match(uri_query, "service=") AND status=200,
1, 0
)
| where is_auth_bypass=1 OR is_admin_access=1
| stats
count AS attempt_count,
min(_time) AS first_seen,
max(_time) AS last_seen,
values(uri_path) AS endpoints,
values(status) AS status_codes
BY src_ip, method, status, host
| eval severity=if(attempt_count > 5, "high", "medium")
| eval alert_name="CVE-2023-27351 PaperCut Auth Bypass Attempt"
| table first_seen, last_seen, host, src_ip, method, status, attempt_count, endpoints, status_codes, severity, alert_name
| sort -attempt_countDetects HTTP requests to PaperCut NG/MF RPC and admin endpoints that are consistent with CVE-2023-27351 improper authentication exploitation, filtering for unauthenticated POST requests to JSON-RPC endpoints returning 200 OK.
Data Sources
Required Sourcetypes
False Positives & Tuning
- Authorized PaperCut administrators performing routine management tasks
- Internal monitoring systems performing health checks against PaperCut endpoints
- Vulnerability scanners or pen testers operating in authorized capacity
- PaperCut application server communicating with its own internal services
Other platforms for CVE-2023-27351
Testing Methodology
Validate this detection against 4 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1CVE-2023-27351 Unauthenticated Health Check Probe
Expected signal: HTTP GET request to /health-check and /api/health on port 9191 from test host IP, HTTP 200 response in web server logs.
- Test 2CVE-2023-27351 Unauthenticated RPC API Call
Expected signal: POST request to /rpc/api/json on port 9191 with Content-Type: application/json header, HTTP 200 response with JSON body in web server logs if vulnerable.
- Test 3CVE-2023-27351 Admin Setup Page Access Attempt
Expected signal: GET request to /app with query parameter service=page/SetupCompleted on port 9191, HTTP response code logged in IIS or PaperCut access logs.
- Test 4CVE-2023-27351 Rapid Sequential Endpoint Enumeration
Expected signal: Multiple sequential HTTP requests to PaperCut endpoints within a short timeframe from a single source IP, visible in web server access logs with timestamps.
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