CVE-2020-1681 in Junos
Summary
by MITRE • 10/17/2020
Receipt of a specifically malformed NDP packet sent from the local area network (LAN) to a device running Juniper Networks Junos OS Evolved can cause the ndp process to crash, resulting in a Denial of Service (DoS). The process automatically restarts without intervention, but a continuous receipt of the malformed NDP packets could leaded to an extended Denial of Service condition. During this time, IPv6 neighbor learning will be affected. The issue occurs when parsing the incoming malformed NDP packet. Rather than simply discarding the packet, the process asserts, performing a controlled exit and restart, thereby avoiding any chance of an unhandled exception. Exploitation of this vulnerability is limited to a temporary denial of service, and cannot be leveraged to cause additional impact on the system. This issue is limited to the processing of IPv6 NDP packets. IPv4 packet processing cannot trigger, and is unaffected by this vulnerability. This issue affects all Juniper Networks Junos OS Evolved versions prior to 20.1R2-EVO. Junos OS is unaffected by this vulnerability.
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Analysis
by VulDB Data Team • 11/20/2020
The vulnerability described in CVE-2020-1681 represents a denial of service weakness within the IPv6 Neighbor Discovery Protocol (NDP) implementation of Juniper Networks Junos OS Evolved systems. This flaw specifically targets the processing of malformed Neighbor Discovery Protocol packets that are transmitted over local area networks, creating a scenario where legitimate network operations can be disrupted through carefully crafted malicious traffic. The vulnerability exists at the network protocol level where the ndp process fails to properly handle malformed packets, leading to system instability and service disruption. The issue demonstrates a classic example of improper input validation where the system does not adequately sanitize incoming network traffic before processing, allowing malformed data to trigger unexpected behavior.
The technical exploitation of this vulnerability occurs when an attacker sends specifically crafted malformed NDP packets to a target device running vulnerable Junos OS Evolved versions. During the packet parsing process, the ndp daemon encounters the malformed data structure and instead of gracefully discarding the packet or implementing proper error handling, it executes an assertion failure that causes the process to terminate and restart automatically. This behavior, while preventing potential unhandled exceptions, creates a denial of service condition as the system must continuously restart the ndp process to maintain network connectivity. The process restarts without requiring manual intervention, but this automatic recovery mechanism becomes problematic when the attacker continuously floods the system with malformed packets, leading to sustained disruption of IPv6 neighbor discovery functionality. This represents a weakness in the system's fault tolerance design where the controlled exit mechanism intended to prevent system crashes actually creates a denial of service scenario through resource exhaustion and service unavailability.
The operational impact of this vulnerability extends beyond simple service interruption to affect core IPv6 networking capabilities within affected systems. When the ndp process crashes and restarts, IPv6 neighbor learning mechanisms become impaired, preventing devices from properly establishing and maintaining IPv6 network connections. This disruption affects all IPv6 traffic flowing through the affected device, potentially compromising network communication for all IPv6-enabled services and applications. Network administrators may experience difficulties in maintaining stable IPv6 connectivity while the system continuously restarts the ndp process, and the automatic restart behavior can mask the underlying attack, making it difficult to identify the source of network instability. The vulnerability is particularly concerning in environments where IPv6 connectivity is critical for business operations, as the disruption can cascade through network infrastructure and affect multiple dependent services.
The mitigation strategy for this vulnerability requires immediate deployment of the patched Junos OS Evolved versions, specifically 20.1R2-EVO or later releases. Organizations should prioritize updating their network infrastructure devices running vulnerable versions to prevent exploitation. Additionally, network administrators can implement packet filtering rules at network boundaries to drop malformed NDP packets before they reach vulnerable systems, though this approach requires careful configuration to avoid disrupting legitimate network traffic. Monitoring systems should be enhanced to detect unusual patterns of ndp process restarts or high volumes of malformed NDP traffic, providing early warning of potential exploitation attempts. This vulnerability aligns with CWE-248, which describes an unchecked exception, and can be mapped to ATT&CK technique T1499.004 for network denial of service attacks. The issue specifically affects only IPv6 NDP packet processing, making it distinct from other network denial of service vulnerabilities that might impact broader network protocols, and represents a targeted weakness in IPv6 implementation rather than a fundamental network stack flaw.
The vulnerability demonstrates how seemingly minor protocol processing errors can result in significant operational impacts within network infrastructure. The design decision to implement assertion failures rather than graceful error handling, while intended to prevent potential security issues from escalating, actually creates a vulnerability that can be exploited for denial of service purposes. This highlights the importance of considering all possible attack vectors during system design phases and implementing robust error handling mechanisms that can gracefully manage malformed inputs without compromising system availability. Organizations should conduct regular vulnerability assessments of their network infrastructure to identify similar weaknesses in protocol implementations, particularly focusing on network services that handle external inputs and maintain continuous operational availability requirements.