CVE-2021-0202 in EX9200
Summary
by MITRE • 01/16/2021
On Juniper Networks MX Series and EX9200 Series platforms with Trio-based MPC (Modular Port Concentrator) where Integrated Routing and Bridging (IRB) interface is configured and it is mapped to a VPLS instance or a Bridge-Domain, certain network events at Customer Edge (CE) device may cause memory leak in the MPC which can cause an out of memory and MPC restarts. When this issue occurs, there will be temporary traffic interruption until the MPC is restored. An administrator can use the following CLI command to monitor the status of memory usage level of the MPC: user@device> show system resource-monitor fpc FPC Resource Usage Summary Free Heap Mem Watermark : 20 % Free NH Mem Watermark : 20 % Free Filter Mem Watermark : 20 % * - Watermark reached Slot # % Heap Free RTT Average RTT 1 87 PFE # % ENCAP mem Free % NH mem Free % FW mem Free 0 NA 88 99 1 NA 89 99 When the issue is occurring, the value of “% NH mem Free” will go down until the MPC restarts. This issue affects MX Series and EX9200 Series with Trio-based PFEs (Packet Forwarding Engines). Please refer to https://kb.juniper.net/KB25385 for the list of Trio-based PFEs. This issue affects Juniper Networks Junos OS on MX Series, EX9200 Series: 17.3R3-S8; 17.4R3-S2; 18.2R3-S4, 18.2R3-S5; 18.3R3-S2, 18.3R3-S3; 18.4 versions starting from 18.4R3-S1 and later versions prior to 18.4R3-S6; 19.2 versions starting from 19.2R2 and later versions prior to 19.2R3-S1; 19.4 versions starting from 19.4R2 and later versions prior to 19.4R2-S3, 19.4R3; 20.2 versions starting from 20.2R1 and later versions prior to 20.2R1-S3, 20.2R2. This issue does not affect Juniper Networks Junos OS: 18.1, 19.1, 19.3, 20.1.
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Analysis
by VulDB Data Team • 02/14/2021
This vulnerability represents a critical memory management flaw in Juniper Networks MX Series and EX9200 Series routers running Trio-based Packet Forwarding Engines. The issue manifests specifically when Integrated Routing and Bridging interfaces are configured and mapped to VPLS instances or Bridge-Domains, creating a scenario where customer edge device network events can trigger systematic memory leaks within the Modular Port Concentrator. The vulnerability operates through a combination of resource exhaustion and improper memory deallocation mechanisms that ultimately lead to complete MPC restarts, causing temporary network disruption.
The technical implementation of this flaw involves the improper handling of network state transitions when CE devices generate specific traffic patterns that interact with the IRB interface configuration. When these conditions are met, the MPC's memory management subsystem fails to properly reclaim memory allocated for Next Hop (NH) structures, leading to progressive memory depletion. The vulnerability is classified under CWE-401 as "Improper Release of Memory Before Removal from Pool" and can be mapped to ATT&CK technique T1499.1 for "Endpoint Denial of Service" as it results in service disruption through resource exhaustion. The memory leak specifically targets the NH memory pool, which is crucial for forwarding decisions in the routing process.
The operational impact of this vulnerability extends beyond simple service interruption to potentially compromise network stability and availability. Network administrators face the challenge of monitoring memory usage through specific CLI commands that track Free Heap Memory, NH Memory, and Filter Memory watermarks. When the % NH mem Free value drops below critical thresholds, typically around 20% as indicated in the monitoring output, the system becomes increasingly vulnerable to complete MPC failure. This creates a cascading effect where network traffic must be rerouted through alternative paths, potentially leading to performance degradation across the entire network segment. The vulnerability affects multiple Junos OS versions, including 17.3R3-S8, 17.4R3-S2, 18.2R3-S4 through 18.2R3-S5, 18.3R3-S2 through 18.3R3-S3, 18.4R3-S1 and later versions prior to 18.4R3-S6, 19.2R2 and later versions prior to 19.2R3-S1, 19.4R2 and later versions prior to 19.4R2-S3 and 19.4R3, and 20.2R1 and later versions prior to 20.2R1-S3 and 20.2R2, making it a widespread concern across multiple release cycles.
Mitigation strategies must focus on both immediate operational responses and long-term architectural considerations. Administrators should implement continuous monitoring using the provided CLI commands to track memory usage patterns and identify potential triggers before complete failures occur. The most effective immediate solution involves applying the relevant Juniper security patches and updates that address the specific memory management issues in the Trio-based MPC implementations. Additionally, network architects should consider reconfiguring IRB interfaces to avoid the problematic VPLS or Bridge-Domain mappings when possible, or implement traffic filtering rules that prevent the specific CE device event patterns that trigger the vulnerability. The remediation approach should also include implementing network segmentation strategies to limit the impact scope and establishing automated alerting systems that notify administrators when memory usage approaches critical thresholds, thereby enabling proactive intervention before complete MPC restarts occur.