CVE-2019-18948 in EOS
Summary
by MITRE
An issue was found in Arista EOS. Specific malformed ARP packets can impact the software forwarding of VxLAN packets. This issue is found in Arista’s EOS VxLAN code, which can allow attackers to crash the VxlanSwFwd agent. This affects EOS 4.21.8M and below releases in the 4.21.x train, 4.22.3M and below releases in the 4.22.x train, 4.23.1F and below releases in the 4.23.x train, and all releases in 4.15, 4.16, 4.17, 4.18, 4.19, 4.20 code train.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 04/17/2020
This vulnerability represents a critical flaw in Arista Enterprise Operating System (EOS) that specifically targets the VxLAN forwarding agent functionality. The issue manifests through malformed Address Resolution Protocol (ARP) packets that can cause the VxlanSwFwd agent to crash, effectively disrupting virtual extensible LAN (VxLAN) packet forwarding operations within the network infrastructure. This represents a significant operational risk as VxLAN is fundamental to software-defined networking and overlay network implementations in enterprise and data center environments. The vulnerability affects multiple release trains of Arista EOS, including the 4.15 through 4.23.x series, with specific versions mentioned as being impacted in the 4.21.x, 4.22.x, and 4.23.x release trains, indicating a widespread exposure across several major software versions.
The technical implementation of this vulnerability stems from insufficient input validation within the VxLAN forwarding code path that processes ARP packets. When malformed ARP packets are received by the system, the VxlanSwFwd agent fails to properly handle the unexpected packet structures, leading to a crash condition that terminates the forwarding agent process. This type of vulnerability falls under the CWE-129 category of "Improper Validation of Array Index" and can be classified as a buffer over-read or improper input validation issue within the network packet processing pipeline. The flaw demonstrates a classic case of insufficient bounds checking in network protocol handling code, where the system does not adequately validate the structure and content of incoming ARP packets before processing them within the VxLAN context.
The operational impact of this vulnerability extends beyond simple service disruption to potentially enable more sophisticated attack scenarios. Network administrators face the risk of denial of service conditions where critical VxLAN traffic is interrupted, affecting virtual machine mobility, network segmentation, and overall data center connectivity. The vulnerability can be exploited by remote attackers who send specifically crafted ARP packets to target affected Arista devices, potentially causing cascading failures in overlay networks where VxLAN is extensively used. This represents a significant concern for cloud providers and enterprises that rely heavily on VxLAN for network virtualization, as such an attack could lead to service degradation or complete network partitioning within affected segments. The vulnerability aligns with ATT&CK technique T1499.004 for network denial of service and could potentially be leveraged as part of broader network disruption campaigns.
Mitigation strategies for this vulnerability require immediate patch management across all affected Arista EOS versions, with the recommended approach being to upgrade to versions that contain the specific fixes for the VxLAN forwarding agent crash issue. Network administrators should implement network segmentation and access controls to limit exposure of affected devices to untrusted networks, while also monitoring for unusual ARP traffic patterns that might indicate exploitation attempts. The Arista security advisory recommends applying the latest patches from the vendor's security bulletin, which typically include enhanced input validation routines and improved error handling within the VxLAN packet processing code. Organizations should also consider implementing network monitoring solutions that can detect and alert on malformed ARP packets or unusual forwarding agent behavior, providing early warning of potential exploitation attempts. Additionally, network redundancy and failover mechanisms should be verified to ensure that the impact of any potential exploitation is minimized through existing network resilience measures.