CVE-2021-0233 in Junos OS
Summary
by MITRE • 04/23/2021
A vulnerability in Juniper Networks Junos OS ACX500 Series, ACX4000 Series, may allow an attacker to cause a Denial of Service (DoS) by sending a high rate of specific packets to the device, resulting in a Forwarding Engine Board (FFEB) crash. Continued receipt of these packets will sustain the Denial of Service (DoS) condition. This issue affects Juniper Networks Junos OS on ACX500 Series, ACX4000 Series: 17.4 versions prior to 17.4R3-S2.
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Analysis
by VulDB Data Team • 04/29/2021
This vulnerability represents a critical denial of service flaw in Juniper Networks Junos OS affecting specific hardware platforms within the ACX series routers. The issue manifests when malicious actors flood the affected devices with a high volume of specially crafted packets designed to exploit a weakness in the Forwarding Engine Board processing logic. The vulnerability specifically impacts versions 17.4R3-S2 and earlier of the Junos OS running on ACX500 and ACX4000 series hardware, creating a persistent DoS condition that can severely disrupt network operations and service availability. The flaw operates at the packet processing level where the device's forwarding engine fails to properly handle certain packet sequences, leading to complete system crashes and requiring manual intervention to restore normal operations.
The technical mechanism behind this vulnerability involves the manipulation of packet flow through the Forwarding Engine Board which serves as the core processing unit for packet forwarding decisions in these routers. When the system receives the targeted packet stream, it triggers an internal state machine failure that causes the FFEB to crash completely, resulting in immediate loss of forwarding capability. The sustained nature of the DoS condition means that once the initial crash occurs, continued receipt of the malicious packet pattern will maintain the device in a crashed state, preventing any legitimate traffic from being processed. This behavior aligns with CWE-122 which describes improper handling of memory allocation and deallocation issues that can lead to system instability and denial of service conditions. The vulnerability demonstrates a classic example of how packet injection attacks can be leveraged to exploit implementation flaws in network infrastructure devices.
The operational impact of this vulnerability extends beyond simple service disruption to encompass significant business continuity risks for organizations relying on these network devices. Network administrators face the challenge of maintaining service availability when an attacker can remotely induce system crashes that require manual intervention and potentially result in extended downtime. The vulnerability affects critical network infrastructure components that often serve as core routing points within enterprise and service provider networks, making the potential impact substantial. Organizations may experience cascading failures as dependent systems lose connectivity, and the need for immediate patch deployment creates operational challenges in large-scale network environments. The issue also presents a significant risk to network security posture, as attackers can exploit this vulnerability to create service disruption while potentially masking other malicious activities.
Mitigation strategies for this vulnerability require immediate implementation of security patches provided by Juniper Networks, specifically targeting the 17.4R3-S2 release or newer versions. Network administrators should prioritize patching affected devices in their environments, particularly those operating in high-risk network segments where such attacks could be leveraged for broader compromise. The recommended approach includes implementing rate limiting and packet filtering rules at network boundaries to reduce the impact of potential attacks, though this provides only temporary relief until proper patches are deployed. Organizations should also consider network segmentation to isolate affected devices and implement monitoring systems to detect unusual packet patterns that may indicate exploitation attempts. From an ATT&CK framework perspective, this vulnerability relates to techniques involving service stoppage and denial of service attacks that can be used as part of broader compromise operations to disable defensive measures and create opportunities for further infiltration. The vulnerability highlights the importance of maintaining current security patches and implementing robust network monitoring to detect and respond to exploitation attempts effectively.