CVE-2017-4920 in NSX-V Edge
Summary
by MITRE
The implementation of the OSPF protocol in VMware NSX-V Edge 6.2.x prior to 6.2.8 and NSX-V Edge 6.3.x prior to 6.3.3 doesn't correctly handle the link-state advertisement (LSA). A rogue LSA may exploit this issue resulting in continuous sending of LSAs between two routers eventually going in loop or loss of connectivity.
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Analysis
by VulDB Data Team • 01/25/2021
The vulnerability identified as CVE-2017-4920 affects the Open Shortest Path First protocol implementation within VMware NSX-V Edge appliances running specific versions of the software. This represents a critical flaw in network protocol handling that can lead to severe operational disruptions in virtualized network environments. The issue specifically manifests in the processing of link-state advertisements which are fundamental components of OSPF functionality used for dynamic routing within network topologies. When properly implemented, OSPF uses LSAs to propagate network topology information between routers, enabling efficient path selection and network convergence. However, the flawed implementation in affected VMware NSX-V Edge versions creates a condition where malformed or malicious LSAs can trigger abnormal behavior in the routing process.
The technical flaw stems from inadequate validation and handling of link-state advertisement packets within the OSPF implementation. When a rogue LSA is received by an affected NSX-V Edge appliance, the system fails to properly validate the advertisement and instead enters a continuous loop of retransmitting the problematic LSA to neighboring routers. This creates a feedback loop where multiple routers continuously exchange the malformed LSA, consuming significant network bandwidth and processing resources. The vulnerability is particularly dangerous because it can be exploited by an attacker who gains access to the network segment or who can inject malicious packets into the OSPF domain. The behavior essentially creates a denial of service condition where legitimate network traffic suffers due to the excessive LSA exchanges, potentially leading to complete loss of network connectivity within the affected routing domain.
The operational impact of this vulnerability extends beyond simple service disruption to encompass broader network reliability and security concerns. Organizations relying on VMware NSX-V Edge appliances for network virtualization and routing functions face significant risks when this vulnerability is exploited. The continuous LSA exchange consumes CPU resources on affected routers, potentially causing performance degradation that impacts other network services. In large-scale deployments, this can cascade into widespread connectivity issues affecting multiple network segments. The vulnerability also creates opportunities for attackers to establish persistent network disruption conditions that can be difficult to diagnose and remediate. Network administrators may observe unusual routing behavior, increased network traffic patterns, and intermittent connectivity issues that appear to be related to routing instability rather than malicious activity. This makes the vulnerability particularly insidious as it can be mistaken for other network problems, delaying proper response and remediation efforts.
Mitigation strategies for CVE-2017-4920 primarily involve upgrading affected VMware NSX-V Edge appliances to versions 6.2.8 or 6.3.3, which contain the necessary patches to properly handle LSA validation and prevent the continuous advertisement loop. Organizations should also implement network segmentation and access controls to limit the exposure of OSPF domains to untrusted networks, as this reduces the attack surface for LSA injection attacks. Network monitoring should be enhanced to detect unusual LSA traffic patterns that may indicate exploitation of this vulnerability. The vulnerability aligns with CWE-248, which addresses "Uncaught Exception" conditions in software implementations, and can be mapped to ATT&CK technique T1059 for execution of malicious code through network protocols. Additionally, this issue relates to the broader category of routing protocol vulnerabilities that can be exploited for network disruption and information gathering activities, making it a significant concern for organizations implementing virtualized network infrastructures.