CVE-2019-1963 in FXOS
Summary
by MITRE
A vulnerability in the Simple Network Management Protocol (SNMP) input packet processor of Cisco FXOS Software and Cisco NX-OS Software could allow an authenticated, remote attacker to cause the SNMP application on an affected device to restart unexpectedly. The vulnerability is due to improper validation of Abstract Syntax Notation One (ASN.1)-encoded variables in SNMP packets. An attacker could exploit this vulnerability by sending a crafted SNMP packet to the SNMP daemon on the affected device. A successful exploit could allow the attacker to cause the SNMP application to restart multiple times, leading to a system-level restart and a denial of service (DoS) condition.
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Analysis
by VulDB Data Team • 12/07/2023
The vulnerability identified as CVE-2019-1963 represents a critical flaw in the SNMP processing functionality of Cisco networking equipment, specifically affecting Cisco FXOS Software and Cisco NX-OS Software implementations. This issue manifests within the Simple Network Management Protocol input packet processor where the system fails to properly validate Abstract Syntax Notation One encoded variables that are integral to SNMP communication protocols. The vulnerability stems from inadequate input sanitization mechanisms that should normally validate the structure and content of ASN.1 encoded data streams before processing them within the SNMP daemon. This weakness creates an exploitable condition where maliciously crafted SNMP packets can be transmitted to targeted devices, potentially causing cascading system failures that compromise network management capabilities.
The technical exploitation of this vulnerability requires an authenticated attacker who can send specifically crafted SNMP packets to the affected device's SNMP daemon service. The flaw exists in the ASN.1 parsing logic where the system does not adequately validate the structure of encoded variables, allowing malformed data to bypass normal input validation checks. When the SNMP daemon processes these malformed packets, the improper ASN.1 validation causes the application to crash or restart unexpectedly. This restart behavior can occur multiple times in succession, creating a persistent denial of service condition that ultimately leads to complete system-level restarts. The vulnerability demonstrates poor error handling and input validation practices that are commonly associated with buffer overflow and parsing vulnerabilities, though this specific case involves application-level protocol handling rather than memory corruption.
From an operational impact perspective, this vulnerability creates significant disruption to network management and monitoring capabilities across affected Cisco devices. The denial of service condition effectively removes the device's ability to participate in SNMP-based network management operations, which are fundamental to network administration and troubleshooting. Network administrators lose visibility into device status, performance metrics, and configuration information, while automated monitoring systems may generate false alerts or fail to detect actual network issues. The repeated application restarts can cause temporary network outages as the device reinitializes its SNMP services, potentially affecting network availability and reliability. Additionally, the system-level restarts may cause loss of configuration data or temporary network disruption that can cascade through dependent network services, particularly in large-scale deployments where multiple devices may be affected simultaneously.
Organizations should implement immediate mitigations including applying the latest security patches provided by Cisco, which address the ASN.1 validation issues in the SNMP packet processing modules. Network segmentation and access controls should be enhanced to limit the attack surface by restricting SNMP access to only trusted management stations. Monitoring systems should be configured to detect unusual SNMP daemon restart patterns and alert administrators to potential exploitation attempts. The vulnerability aligns with CWE-20, which describes improper input validation, and maps to ATT&CK technique T1499.004 for network denial of service attacks. Additional defensive measures include implementing SNMPv3 with strong authentication and encryption, disabling unnecessary SNMP services on devices that do not require them, and configuring rate limiting on SNMP traffic to prevent rapid exploitation attempts. Regular security assessments and vulnerability scanning should be conducted to identify other potential SNMP-related vulnerabilities in the network infrastructure, as this issue demonstrates the importance of proper protocol implementation in network management services.