CVE-2018-0063 in Junos
Summary
by MITRE
A vulnerability in the IP next-hop index database in Junos OS 17.3R3 may allow a flood of ARP requests, sent to the management interface, to exhaust the private Internal routing interfaces (IRIs) next-hop limit. Once the IRI next-hop database is full, no further next hops can be learned and existing entries cannot be cleared, leading to a sustained denial of service (DoS) condition. An indicator of compromise for this issue is the report of the following error message: %KERN-4: Nexthop index allocation failed: private index space exhausted This issue only affects the management interface, and does not impact regular transit traffic through the FPCs. This issue also only affects Junos OS 17.3R3. No prior versions of Junos OS are affected by this issue. Affected releases are Juniper Networks Junos OS: 17.3R3.
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Analysis
by VulDB Data Team • 05/25/2023
This vulnerability resides in the IP next-hop index database implementation within Junos OS version 17.3R3, specifically affecting the management interface's handling of ARP requests. The flaw represents a classic resource exhaustion attack vector where malicious actors can flood the system with ARP requests to trigger a denial of service condition. The vulnerability is particularly concerning because it targets the internal routing infrastructure rather than external network traffic, making it difficult to detect through conventional network monitoring. The issue stems from inadequate bounds checking and memory management within the next-hop database allocation mechanism, which fails to properly handle high volumes of incoming ARP traffic on the management interface.
The technical implementation flaw manifests as a limitation in the private Internal routing interfaces (IRIs) next-hop database capacity. When the management interface receives a flood of ARP requests, it triggers the exhaustion of the private index space allocated for next-hop entries. This behavior violates the expected resource management principles outlined in CWE-770, which addresses allocation of resources without proper bounds checking. The system's inability to dynamically adjust or clear existing entries once the database reaches capacity creates a persistent DoS condition that cannot be resolved through normal operational procedures. The specific error message %KERN-4: Nexthop index allocation failed: private index space exhausted serves as a definitive indicator that this vulnerability has been successfully exploited, aligning with the ATT&CK technique T1499.002 for network denial of service attacks.
The operational impact of this vulnerability extends beyond simple service disruption as it fundamentally compromises the management capabilities of the affected device. Network administrators lose the ability to maintain routing table integrity and cannot learn new next-hop entries, effectively rendering the management interface non-functional for routing purposes. This condition persists until the device is manually rebooted, creating extended downtime windows that can severely impact network operations and security posture. The vulnerability's restriction to the management interface means that regular transit traffic through the Forwarding Processing Cards (FPCs) remains unaffected, but this does not mitigate the overall security risk as the management plane is critical for device configuration and monitoring. The specific version targeting, Junos OS 17.3R3, indicates this was likely a regression introduced in a specific release cycle rather than a fundamental architectural flaw.
Mitigation strategies must focus on both immediate protective measures and long-term architectural improvements. Network administrators should implement rate limiting on ARP requests to the management interface, deploy intrusion detection systems to monitor for the specific error message pattern, and ensure proper network segmentation to isolate management traffic. The recommended approach involves upgrading to patched versions of Junos OS where the next-hop database allocation has been properly bounded and the system can handle resource exhaustion scenarios more gracefully. Organizations should also consider implementing redundant management paths and ensuring that critical network devices have proper failover mechanisms in place. The vulnerability demonstrates the importance of proper resource management in operating system kernels and highlights the need for comprehensive testing of edge cases in routing table implementations, particularly those involving management interfaces where security and availability are paramount.