CVE-2020-1638 in Junos
Summary
by MITRE
The FPC (Flexible PIC Concentrator) of Juniper Networks Junos OS and Junos OS Evolved may restart after processing a specific IPv4 packet. Only packets destined to the device itself, successfully reaching the RE through existing edge and control plane filtering, will be able to cause the FPC restart. When this issue occurs, all traffic via the FPC will be dropped. By continuously sending this specific IPv4 packet, an attacker can repeatedly crash the FPC, causing an extended Denial of Service (DoS) condition. This issue can only occur when processing a specific IPv4 packet. IPv6 packets cannot trigger this issue. This issue affects: Juniper Networks Junos OS on MX Series with MPC10E or MPC11E and PTX10001: 19.2 versions prior to 19.2R1-S4, 19.2R2; 19.3 versions prior to 19.3R2-S2, 19.3R3; 19.4 versions prior to 19.4R1-S1, 19.4R2. Juniper Networks Junos OS Evolved on on QFX5220, and PTX10003 series: 19.2-EVO versions; 19.3-EVO versions; 19.4-EVO versions prior to 19.4R2-EVO. This issue does not affect Junos OS versions prior to 19.2R1. This issue does not affect Junos OS Evolved versions prior to 19.2R1-EVO.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 05/17/2024
The vulnerability described in CVE-2020-1638 represents a critical Denial of Service weakness within the Flexible PIC Concentrator (FPC) component of Juniper Networks Junos OS and Junos OS Evolved operating systems. This flaw specifically targets the packet processing mechanisms of network devices, particularly those in the MX Series with MPC10E or MPC11E line cards and PTX10001 platforms, as well as QFX5220 and PTX10003 series devices running the evolved operating system. The vulnerability manifests when the FPC receives and processes a specially crafted IPv4 packet that is destined for the device itself, requiring the packet to successfully traverse existing edge and control plane filtering mechanisms to reach the Routing Engine. This specific requirement for packet delivery through established filtering paths creates a narrow but exploitable attack surface that security professionals must understand.
The technical implementation of this vulnerability stems from improper handling of certain IPv4 packet structures within the FPC's packet processing pipeline. When the FPC encounters this specific packet type, it triggers an internal restart mechanism that causes the entire FPC to reboot. This restart event results in complete traffic disruption across the affected FPC, as all network traffic flowing through that processing unit is dropped until the system recovers. The vulnerability is particularly concerning because it only affects IPv4 packets, with IPv6 packets being immune to this specific issue, suggesting a targeted flaw in the IPv4 processing code path rather than a broader architectural weakness. The affected versions span multiple release branches including 19.2, 19.3, and 19.4, with specific patches required for each version line to address the issue properly.
From an operational impact perspective, this vulnerability creates a persistent DoS condition that can be maintained indefinitely through continuous packet injection attacks. An attacker capable of sending the specific IPv4 packet pattern can repeatedly crash the FPC, effectively maintaining service disruption without requiring additional authentication or access privileges beyond the ability to reach the device's network interface. The severity of this impact is amplified by the fact that the FPC restart affects all traffic passing through that unit, potentially compromising entire network segments or routing paths that depend on the affected hardware components. This vulnerability directly maps to CWE-20, representing a weakness in input handling where the system fails to properly validate or handle specific packet structures, and aligns with ATT&CK technique T1498, which encompasses network denial of service attacks that disrupt availability of systems and services.
Mitigation strategies for CVE-2020-1638 require immediate implementation of software patches provided by Juniper Networks for all affected versions of Junos OS and Junos OS Evolved. Organizations should prioritize patching devices running versions prior to the specified release points including 19.2R1-S4, 19.3R2-S2, and 19.4R1-S1, with particular attention to the QFX5220 and PTX10003 series running the evolved operating system. Network administrators should also consider implementing additional protective measures such as ingress filtering to prevent unauthorized access to the device's network interfaces, though the vulnerability's requirement for packets to traverse existing filtering mechanisms limits the effectiveness of such approaches. The patching process should be carefully coordinated to minimize service disruption, with particular attention to the fact that the vulnerability affects critical routing infrastructure components. Security monitoring should include detection of unusual packet patterns that might indicate exploitation attempts, while network segmentation and redundancy planning should account for the potential for sustained service disruption during exploitation periods.