CVE-2021-0259 in Junos OS Evolved
Summary
by MITRE • 04/23/2021
Due to a vulnerability in DDoS protection in Juniper Networks Junos OS and Junos OS Evolved on QFX5K Series switches in a VXLAN configuration, instability might be experienced in the underlay network as a consequence of exceeding the default ddos-protection aggregate threshold. If an attacker on a client device on the overlay network sends a high volume of specific, legitimate traffic in the overlay network, due to an improperly detected DDoS violation, the leaf might not process certain L2 traffic, sent by spines in the underlay network. Continued receipt and processing of the high volume traffic will sustain the Denial of Service (DoS) condition. This issue affects: Juniper Networks Junos OS on QFX5K Series: 17.3 versions prior to 17.3R3-S11; 17.4 versions prior to 17.4R3-S5; 18.1 versions prior to 18.1R3-S13; 18.2 versions prior to 18.2R2-S8, 18.2R3-S8; 18.3 versions prior to 18.3R3-S5; 18.4 versions prior to 18.4R1-S8, 18.4R2-S6, 18.4R3-S6; 19.1 versions prior to 19.1R3-S4; 19.2 versions prior to 19.2R1-S6, 19.2R3-S2; 19.3 versions prior to 19.3R3-S2; 19.4 versions prior to 19.4R2-S4, 19.4R3-S1; 20.1 versions prior to 20.1R2; 20.2 versions prior to 20.2R2; 20.3 versions prior to 20.3R1-S2, 20.3R2. Juniper Networks Junos OS Evolved on QFX5220: All versions prior to 20.3R2-EVO.
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Analysis
by VulDB Data Team • 04/27/2021
This vulnerability resides within the distributed denial of service protection mechanisms of juniper networks junos os and junos os evolved operating systems deployed on qfx5k series switches. the flaw manifests specifically in vxlan configurations where the system incorrectly identifies legitimate overlay network traffic as malicious ddos attacks. this misclassification occurs when an attacker generates high volumes of what appears to be legitimate traffic within the overlay network, causing the system to trigger inappropriate ddos protection measures. the vulnerability stems from an improperly configured ddos-protection aggregate threshold that fails to accurately distinguish between normal network behavior and actual malicious activity, leading to cascading failures in network stability.
The technical implementation of this vulnerability involves the interaction between overlay and underlay network layers within vxlan environments. when legitimate traffic exceeds the default ddos protection thresholds, the system's detection algorithms incorrectly flag this activity as a ddos violation. this misidentification results in the leaf switches failing to properly process certain layer 2 traffic originating from spine devices in the underlay network. the root cause can be traced to inadequate traffic analysis and threshold management within the ddos protection subsystem, which lacks sufficient context awareness to differentiate between normal network load and actual malicious traffic patterns. this issue is particularly concerning as it affects multiple version streams across different release cycles, indicating a fundamental design flaw rather than a simple implementation error.
The operational impact of this vulnerability extends beyond simple network disruption to create sustained denial of service conditions that can severely compromise network availability and performance. when the system incorrectly identifies legitimate traffic as ddos attacks, it begins to drop or delay processing of critical underlay network communications, effectively creating network partitions and service degradation. the continued receipt and processing of high-volume traffic maintains the dos condition, making it difficult for network administrators to restore normal operations. this vulnerability particularly affects large-scale data center networks where qfx5k switches serve as critical forwarding elements between spine and leaf nodes, potentially causing widespread service outages across the entire network infrastructure. the attack vector is relatively simple to execute, requiring only the generation of specific legitimate traffic patterns that exceed the default thresholds.
Network security professionals should implement immediate mitigations including updating to the patched versions specified in the advisory, which address the ddos protection threshold configurations and improve traffic analysis algorithms. organizations should also consider implementing additional monitoring and alerting mechanisms to detect abnormal traffic patterns that might trigger similar false positives. the vulnerability aligns with common weakness enumeration cwecwe-20 and follows attack technique patterns described in the attack tree framework where adversaries can exploit system misconfigurations to achieve persistent denial of service conditions. network administrators should review their current ddos protection policies and consider implementing more granular threshold configurations that better account for legitimate network traffic patterns in vxlan environments. additional defensive measures include implementing traffic shaping and rate limiting at the overlay network level to prevent legitimate traffic from reaching problematic threshold levels while maintaining network performance and security posture.