CVE-2019-9931 in Printer
Summary
by MITRE
Various Lexmark printers contain a denial of service vulnerability in the SNMP service that can be exploited to crash the device.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 08/08/2020
The CVE-2019-9931 vulnerability represents a critical denial of service flaw affecting multiple Lexmark printer models that operate with SNMP (Simple Network Management Protocol) services. This vulnerability resides within the network management infrastructure of these devices, specifically targeting the SNMP implementation that allows administrators to monitor and manage printer operations across networks. The flaw manifests when the SNMP service processes malformed or specially crafted requests that trigger unexpected behavior in the printer's operating system, ultimately leading to complete service disruption. According to CWE-129, this vulnerability falls under the category of improper input validation, where the system fails to properly validate or sanitize incoming SNMP packets before processing them. The affected Lexmark printers typically include various models from their multifunctional and laser printer lines that support SNMP for remote monitoring and management purposes. The vulnerability's exploitation does not require authentication or specialized privileges, making it particularly dangerous as any network-accessible entity can potentially trigger the denial of service condition.
The technical implementation of this vulnerability stems from insufficient bounds checking within the SNMP service daemon of affected Lexmark devices. When legitimate SNMP requests are received, the system fails to properly validate the length and structure of incoming packets before attempting to parse them. This allows attackers to craft malicious SNMP packets containing oversized or malformed data sequences that cause buffer overflows or memory corruption within the printer's processing stack. The SNMP service, which typically operates on UDP port 161, becomes unstable when processing these malformed packets and subsequently crashes or becomes unresponsive. The printer's operating system, which runs on embedded Linux variants, lacks proper exception handling mechanisms to gracefully recover from such malformed input sequences. This behavior aligns with ATT&CK technique T1499.001, which describes denial of service attacks targeting network services and protocols. The vulnerability creates a persistent state where the printer becomes unavailable for legitimate network management operations, effectively rendering the device unusable for its intended purpose until manual intervention or power cycling occurs.
The operational impact of CVE-2019-9931 extends beyond simple service interruption to encompass significant business continuity risks for organizations relying on Lexmark printer fleets. In enterprise environments where multiple printers are managed through centralized SNMP monitoring systems, a single vulnerable device can cause cascading failures in network management infrastructure. The vulnerability particularly affects organizations that depend on printer status monitoring, toner level tracking, and remote configuration capabilities. When exploited, the denial of service condition can persist until the affected printer is physically rebooted or the SNMP service is manually restarted, creating operational downtime that can range from minutes to hours depending on the organization's response procedures. Network administrators may experience false alarms and system alerts when SNMP monitoring tools detect the unresponsive printer, leading to unnecessary troubleshooting efforts. The vulnerability's exploitation can also impact print queue management systems that rely on SNMP for printer status updates, potentially causing print jobs to fail or queue indefinitely. According to industry best practices outlined in NIST SP 800-41, network administrators should implement proper network segmentation and access controls to limit exposure to such vulnerabilities. Organizations using affected Lexmark devices should consider implementing network monitoring solutions that can detect unusual SNMP traffic patterns and automatically alert administrators to potential exploitation attempts.
Mitigation strategies for CVE-2019-9931 should focus on both immediate defensive measures and long-term architectural improvements. The most effective immediate solution involves applying firmware updates provided by Lexmark, which typically include patched SNMP service implementations with proper input validation and bounds checking mechanisms. Organizations should also implement network access controls through firewalls and access control lists to restrict SNMP traffic to authorized management systems only, thereby reducing the attack surface. Network segmentation strategies should isolate printer networks from general business networks to limit potential exploitation vectors. The implementation of SNMPv3 with authentication and encryption can provide additional protection against unauthorized access to printer management functions. Organizations should also deploy network monitoring solutions capable of detecting anomalous SNMP traffic patterns that may indicate exploitation attempts. According to MITRE ATT&CK framework, this vulnerability should be monitored as part of broader network defense strategies against service disruption attacks. Regular vulnerability assessments and penetration testing should include verification of SNMP service configurations and firmware versions to ensure compliance with security baselines. Additionally, implementing network intrusion detection systems with signature-based rules specifically targeting known SNMP exploitation patterns can provide early warning capabilities. The remediation process should also include establishing incident response procedures for handling printer-related denial of service events, ensuring rapid recovery and minimal business impact. Organizations should maintain updated inventories of all networked printers and their firmware versions to facilitate rapid identification and remediation of vulnerable devices.