1. Introduction
WinComLPD LPD Monitoring Server Detection indicates a printer control service is listening on your network. This service manages remote print queues using WinComLPD Total, a commercial Line Printer Daemon application for Windows. It presents a potential risk as it allows external access to printing services, which could be misused. Confidentiality, integrity and availability may all be impacted if exploited.
2. Technical Explanation
The vulnerability stems from the LPD Monitoring Server port being open on the remote host. This service is designed for remote print queue management but can expose systems to unwanted access. An attacker could potentially gain control of printing services or use them as a pivot point into the network.
- Root cause: The LPD monitoring server is listening on a public interface without restriction.
- Exploit mechanism: An attacker could send crafted commands to the open port to manage print queues, potentially executing arbitrary code or gaining access to sensitive information. For example, an attacker might attempt to list available printers and users.
- Scope: Windows systems running WinComLPD Total are affected.
3. Detection and Assessment
You can confirm if a system is vulnerable by checking for the listening service and identifying its version. A quick check involves using network scanning tools, while thorough assessment requires examining the WinComLPD configuration.
- Quick checks: Use
netstat -an | find "515"to see if port 515 is open. - Scanning: Nessus plugin ID 93876 may detect this service. This is an example only, results can vary.
- Logs and evidence: Check WinComLPD logs for connections from unexpected sources. Log files are typically located in the WinComLPD installation directory.
netstat -an | find "515"4. Solution / Remediation Steps
To fix this issue, limit incoming traffic to the LPD monitoring port if it is not required for business operations. If needed, restrict access only to trusted networks or hosts.
4.1 Preparation
- Ensure you have administrator privileges to modify firewall rules and WinComLPD settings. A roll back plan is to restore the backed-up configuration file and restart the service.
- A change window may be needed depending on your environment, with approval from IT management.
4.2 Implementation
- Step 1: Open Windows Firewall with Advanced Security.
- Step 2: Create a new inbound rule to block TCP port 515 for all networks except trusted ones.
- Step 3: Configure the rule to allow connections only from specific IP addresses or subnets if required.
- Step 4: Test connectivity from allowed hosts and verify that access is blocked from others.
4.3 Config or Code Example
Before
(Port 515 open on all interfaces)After
(Port 515 blocked by Windows Firewall except for trusted IP addresses)4.4 Security Practices Relevant to This Vulnerability
Several security practices can help prevent this issue. Least privilege reduces the impact of exploitation, while network segmentation limits access to sensitive services.
- Practice 1: Implement least privilege principles by granting only necessary permissions to WinComLPD and its users.
- Practice 2: Use network segmentation to isolate printing services from critical systems.
4.5 Automation (Optional)
# PowerShell example to block port 515 using New-NetFirewallRule
New-NetFirewallRule -DisplayName "Block WinComLPD LPD" -Direction Inbound -Protocol TCP -LocalPort 515 -Action Block
5. Verification / Validation
Confirm the fix by checking that port 515 is blocked from untrusted sources and accessible only from allowed hosts. A smoke test involves printing a document successfully from an authorized machine.
- Post-fix check: Run
netstat -an | find "515"again, it should not show the port listening on all interfaces. - Re-test: Re-run the earlier detection method (
netstat -an | find "515") to confirm the service is no longer exposed. - Smoke test: Print a document from an authorized machine to verify printing functionality remains intact.
- Monitoring: Monitor Windows Firewall logs for blocked connections on port 515 as an example of regression detection.
netstat -an | find "515"6. Preventive Measures and Monitoring
Update security baselines to include restrictions on unnecessary listening services like LPD monitoring. Implement CI/CD pipeline checks to prevent the same configuration fault in future deployments, for example using a policy checker.
- Baselines: Update your Windows Security Baseline or CIS benchmark to reflect restricted access to port 515.
- Asset and patch process: Review configurations during regular asset audits, with a monthly review cycle recommended.
7. Risks, Side Effects, and Roll Back
- Risk or side effect 1: Disruption of printing services for authorized users if the rule is too restrictive. Mitigation: Carefully identify and allow necessary IP addresses.
- Roll back: Remove the newly created firewall rule and restart the WinComLPD service.
8. References and Resources
- Vendor advisory or bulletin: http://clientsoftware.com.au/lpd.html