CVE-2019-1840 in Prime Network Registrar
Summary
by MITRE
A vulnerability in the DHCPv6 input packet processor of Cisco Prime Network Registrar could allow an unauthenticated, remote attacker to restart the server and cause a denial of service (DoS) condition on the affected system. The vulnerability is due to incomplete user-supplied input validation when a custom extension attempts to change a DHCPv6 packet received by the application. An attacker could exploit this vulnerability by sending malformed DHCPv6 packets to the application. An exploit could allow the attacker to trigger a restart of the service which, if exploited repeatedly, might lead to a DoS condition. This vulnerability can only be exploited if the administrator of the server has previously installed custom extensions that attempt to modify the packet details before the packet has been processed. Note: Although the CVSS score matches a High SIR, this has been lowered to Medium because this condition will only affect an application that has customer-developed extensions that will attempt to modify packet parameters before the packet has been completely sanitized. If packet modification in a custom extension happens after the packet has been sanitized, the application will not be affected by this vulnerability. Software versions prior to 8.3(7) and 9.1(2) are affected.
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Analysis
by VulDB Data Team • 09/04/2023
The vulnerability identified as CVE-2019-1840 resides within the DHCPv6 input packet processor of Cisco Prime Network Registrar, representing a significant security weakness that enables unauthenticated remote attackers to execute denial of service attacks against affected systems. This flaw specifically targets the validation mechanisms employed when custom extensions attempt to modify DHCPv6 packets received by the application, creating a pathway for malicious actors to disrupt network services through carefully crafted malformed packets. The vulnerability operates at the intersection of input validation and packet processing, where insufficient sanitization of user-supplied data creates exploitable conditions that can be leveraged for service disruption.
The technical implementation of this vulnerability stems from incomplete input validation procedures within the DHCPv6 packet processing pipeline, particularly when custom extensions are present in the system configuration. When administrators install custom extensions designed to modify packet details prior to full packet sanitization, these extensions become vulnerable to malformed input that can trigger unexpected behavior within the application's processing logic. The flaw manifests when the application attempts to process DHCPv6 packets that contain unexpected or malformed data structures, causing the system to restart automatically as a protective mechanism against corrupted packet processing. This behavior aligns with CWE-20, which describes improper input validation as a fundamental weakness that can lead to various security issues including service disruption and system instability. The vulnerability's exploitation requires the presence of custom extensions that perform packet modifications before sanitization, making it conditional on specific deployment configurations rather than affecting all installations uniformly.
The operational impact of CVE-2019-1840 extends beyond simple service interruption to potentially create sustained denial of service conditions that can severely impact network infrastructure operations. Attackers can repeatedly exploit this vulnerability to force continuous service restarts, effectively rendering the affected DHCPv6 server incapable of providing network services to clients. The vulnerability's conditional nature means that organizations with default configurations or those that have properly sanitized packet processing before extension execution remain unaffected, but those that have implemented custom extensions for packet modification face significant risk. This characteristic places the vulnerability in the ATT&CK framework under the T1499.004 technique for Network Denial of Service, where attackers leverage application-level vulnerabilities to disrupt network services. The CVSS score reduction from High to Medium reflects the conditional requirements for exploitation, but the actual operational risk remains substantial for affected deployments.
Mitigation strategies for CVE-2019-1840 focus primarily on addressing the root cause through proper software updates and configuration management. Organizations should immediately upgrade to Cisco Prime Network Registrar versions 8.3(7) or 9.1(2) or later, which contain patches specifically designed to address the incomplete input validation issue. System administrators must also conduct thorough reviews of existing custom extensions to identify those that perform packet modifications prior to sanitization, and either remove or modify these extensions to ensure proper input validation occurs before any packet manipulation. The remediation process should include implementing network monitoring to detect unusual restart patterns that might indicate exploitation attempts, as well as establishing secure coding practices for custom extension development that prioritize input sanitization before any packet processing operations. Additionally, organizations should consider implementing network segmentation and access controls to limit exposure of vulnerable systems to untrusted network segments, reducing the attack surface available to potential adversaries seeking to exploit this vulnerability.