CVE-2019-1918 in IOS XR
Summary
by MITRE
A vulnerability in the implementation of Intermediate System–to–Intermediate System (IS–IS) routing protocol functionality in Cisco IOS XR Software could allow an unauthenticated attacker who is in the same IS-IS area to cause a denial of service (DoS) condition. The vulnerability is due to incorrect processing of IS–IS link-state protocol data units (PDUs). An attacker could exploit this vulnerability by sending specific link-state PDUs to an affected system to be processed. A successful exploit could allow the attacker to cause incorrect calculations used in the weighted remote shared risk link groups (SRLG) or in the IGP Flexible Algorithm. It could also cause tracebacks to the logs or potentially cause the receiving device to crash the IS–IS process, resulting in a DoS condition.
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Analysis
by VulDB Data Team • 11/21/2023
The vulnerability identified as CVE-2019-1918 resides within the Intermediate System-to-Intermediate System (IS-IS) routing protocol implementation of Cisco IOS XR Software, representing a critical security flaw that undermines network infrastructure stability. This issue specifically affects the processing of IS-IS link-state protocol data units (PDUs) and demonstrates how fundamental routing protocol mechanisms can be exploited to compromise network availability. The vulnerability is particularly concerning because it operates at the core of network routing functionality, where even minor flaws can cascade into significant service disruptions across interconnected systems. The affected software operates within the realm of enterprise and service provider networks where IS-IS protocol serves as a critical component for internal routing decisions.
The technical flaw manifests in the incorrect handling of IS-IS link-state PDUs, which are essential for maintaining network topology information and enabling dynamic routing decisions. When an attacker crafts and injects specific malformed PDUs into the same IS-IS area, the vulnerable system processes these packets incorrectly, leading to erroneous calculations within the weighted remote shared risk link groups (SRLG) and IGP Flexible Algorithm implementations. This improper packet processing creates a condition where the system's internal routing calculations become corrupted, potentially triggering cascading failures in the routing protocol's operation. The vulnerability's exploitation mechanism relies on the attacker's ability to send precisely constructed PDUs that cause the system to perform invalid operations during the link-state database processing, which is a fundamental aspect of IS-IS protocol behavior.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise the entire network routing infrastructure. A successful exploitation can result in denial of service conditions that affect network availability and performance, as the IS-IS process may crash or become unstable, requiring manual intervention for recovery. The vulnerability's effects can manifest as tracebacks in system logs, indicating the specific points where the processing failures occurred, and may ultimately lead to complete routing protocol failure within the affected device. Network administrators face the challenge of identifying and mitigating this vulnerability without disrupting ongoing network operations, as the attack can be executed by an unauthenticated remote attacker within the same IS-IS area, eliminating the need for complex access privileges.
Mitigation strategies for CVE-2019-1918 typically involve applying official Cisco security patches and updates that address the specific packet processing flaws within the IS-IS implementation. Network administrators should also implement monitoring solutions to detect anomalous IS-IS PDU traffic patterns that may indicate exploitation attempts. The vulnerability aligns with CWE-129, which addresses improper validation of input boundaries, and demonstrates characteristics consistent with ATT&CK technique T1499.002 for network denial of service attacks. Organizations should consider implementing access control measures to limit IS-IS neighbor relationships to trusted devices and employ network segmentation strategies to isolate potentially vulnerable routing equipment. Additionally, regular security assessments and network traffic analysis should be conducted to identify any potential exploitation attempts and maintain awareness of the evolving threat landscape surrounding routing protocol vulnerabilities.