CVE-2020-1603 in Junos
Summary
by MITRE
Specific IPv6 packets sent by clients processed by the Routing Engine (RE) are improperly handled. These IPv6 packets are designed to be blocked by the RE from egressing the RE. Instead, the RE allows these specific IPv6 packets to egress the RE, at which point a mbuf memory leak occurs within the Juniper Networks Junos OS device. This memory leak eventually leads to a kernel crash (vmcore), or the device hanging and requiring a power cycle to restore service, creating a Denial of Service (DoS) condition. During the time where mbufs are rising, yet not fully filled, some traffic from client devices may begin to be black holed. To be black holed, this traffic must match the condition where this traffic must be processed by the RE. Continued receipt and attempted egress of these specific IPv6 packets from the Routing Engine (RE) will create an extended Denial of Service (DoS) condition. Scenarios which have been observed are: 1. In a single chassis, single RE scenario, the device will hang without vmcore, or a vmcore may occur and then hang. In this scenario the device needs to be power cycled. 2. In a single chassis, dual RE scenario, the device master RE will fail over to the backup RE. In this scenario, the master and the backup REs need to be reset from time to time when they vmcore. There is no need to power cycle the device. 3. In a dual chassis, single RE scenario, the device will hang without vmcore, or a vmcore may occur and then hang. In this scenario, the two chassis' design relies upon some type of network level redundancy - VRRP, GRES, NSR, etc. - 3.a In a commanded switchover, where nonstop active routing (NSR) is enabled no session loss is observed. 4. In a dual chassis, dual chassis scenario, rely upon the RE to RE failover as stated in the second scenario. In the unlikely event that the device does not switch RE to RE gracefully, then the fallback position is to the network level services scenario in the third scenario. This issue affects: Juniper Networks Junos OS 16.1 versions prior to 16.1R7-S6; 16.1 version 16.1X70-D10 and later; 16.2 versions prior to 16.2R2-S11; 17.1 versions prior to 17.1R2-S11, 17.1R3-S1; 17.2 versions prior to 17.2R1-S9, 17.2R2-S8, 17.2R3-S3; 17.3 versions prior to 17.3R3-S6; 17.4 versions prior to 17.4R2-S9, 17.4R3; 18.1 versions prior to 18.1R3-S7; 18.2 versions prior to 18.2R3-S2; 18.2X75 versions prior to 18.2X75-D50, 18.2X75-D410; 18.3 versions prior to 18.3R1-S6, 18.3R2-S2, 18.3R3; 18.4 versions prior to 18.4R1-S6, 18.4R2-S2, 18.4R3; 19.1 versions prior to 19.1R1-S3, 19.1R2; 19.2 versions prior to 19.2R1-S2, 19.2R2. This issue does not affect releases prior to Junos OS 16.1R1.
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Analysis
by VulDB Data Team • 03/24/2024
The vulnerability described in CVE-2020-1603 represents a critical memory management flaw within Juniper Networks Junos OS routing engines that specifically impacts IPv6 packet processing. This issue manifests when certain IPv6 packets designed to be blocked by the Routing Engine (RE) are improperly handled, allowing them to egress the device instead of being properly dropped. The fundamental technical flaw resides in the mbuf memory allocation system where these improperly processed packets trigger memory leaks within the kernel space. According to CWE-122, this vulnerability directly relates to improper restriction of operations within a memory buffer, creating a condition where kernel memory becomes progressively consumed without proper cleanup mechanisms.
The operational impact of this vulnerability creates severe denial of service conditions that can manifest in multiple scenarios depending on the device configuration and deployment topology. When mbuf memory leaks occur, the system experiences progressive memory exhaustion that eventually leads to kernel crashes generating vmcore dumps or complete device hangs requiring power cycling. The vulnerability's behavior is particularly concerning because it affects traffic that must be processed by the RE, meaning legitimate routing operations become disrupted as the device struggles with memory management. During the memory leak phase, some client traffic begins to experience black holing where packets are silently dropped rather than properly routed, creating intermittent service degradation that can persist until the device is reset.
Network redundancy scenarios compound the complexity of this vulnerability's impact across different deployment configurations. In single chassis single RE environments, the device typically hangs without generating vmcore dumps, requiring complete power cycling for recovery, while dual RE scenarios trigger automatic failover mechanisms that may require periodic resets of both master and backup routing engines. The dual chassis deployments introduce additional complexity with dependency on network level redundancy protocols such as VRRP, GRES, and NSR, where the graceful failover mechanisms may prevent session loss during switchover operations but still require manual intervention when vmcore conditions occur. This behavior aligns with ATT&CK technique T1499.004, which involves network denial of service attacks targeting memory exhaustion and system stability.
The vulnerability affects a broad range of Junos OS versions across multiple release branches, indicating this is not an isolated incident but rather a persistent flaw in the memory management architecture. The specific versions affected include multiple release streams from 16.1 through 19.2, demonstrating that this memory leak issue has been present across several major release cycles and has not been adequately addressed in the affected software versions. The vulnerability's persistence across such a wide range of releases suggests that the underlying memory management implementation contains fundamental design flaws that require comprehensive architectural review and patching. Organizations should prioritize immediate remediation of affected systems to prevent potential service disruption, as the vulnerability creates conditions where network availability is compromised through memory exhaustion rather than direct attack vectors, making it particularly insidious in production environments where network stability is paramount.