CVE-2020-1651 in Junos MX
Summary
by MITRE
On Juniper Networks MX series, receipt of a stream of specific Layer 2 frames may cause a memory leak resulting in the packet forwarding engine (PFE) on the line card to crash and restart, causing traffic interruption. By continuously sending this stream of specific layer 2 frame, an attacker connected to the same broadcast domain can repeatedly crash the PFE, causing a prolonged Denial of Service (DoS). This issue affects Juniper Networks Junos OS on MX Series: 17.2 versions prior to 17.2R3-S4; 17.2X75 versions prior to 17.2X75-D105.19; 17.3 versions prior to 17.3R3-S7; 17.4 versions prior to 17.4R1-S3, 17.4R2; 18.1 versions prior to 18.1R2. This issue does not affect Juniper Networks Junos OS releases prior to 17.2R1.
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Analysis
by VulDB Data Team • 11/04/2020
This vulnerability represents a critical memory management flaw in Juniper Networks MX series routers that specifically targets the packet forwarding engine component. The issue manifests when the system receives a carefully crafted stream of Layer 2 frames that exploit a memory leak condition within the forwarding engine processing logic. The vulnerability affects multiple Junos OS versions across the 17.x and 18.1 release lines, with specific patch thresholds defined for each major version. This memory leak condition causes the packet forwarding engine to consume excessive memory resources until it reaches a critical threshold that triggers an automatic restart of the PFE component. The operational impact extends beyond simple service interruption as the system's ability to forward packets becomes compromised, leading to complete traffic disruption on affected line cards. The vulnerability's classification aligns with CWE-401: Improper Release of Memory and CWE-119: Improper Access to Memory, both of which relate to memory management failures that can lead to system instability and denial of service conditions.
The attack vector for this vulnerability requires an adversary to be within the same broadcast domain as the targeted MX series router, which significantly reduces the attack surface but does not eliminate the risk entirely. An attacker can repeatedly send the specific Layer 2 frame patterns to continuously trigger the memory leak condition, creating a sustained denial of service scenario that can persist until the affected PFE is manually restarted or the device is rebooted. This persistent nature of the attack makes it particularly dangerous in network environments where continuous availability is critical. The vulnerability demonstrates characteristics consistent with ATT&CK technique T1499.004: Endpoint Denial of Service, where an attacker targets specific system components to cause service disruption. The fact that this issue does not affect Junos OS releases prior to 17.2R1 suggests that the memory management improvements introduced in that version were insufficient to prevent this particular class of memory leak.
The operational consequences of this vulnerability extend far beyond simple network disruption as it affects the fundamental packet forwarding capabilities of the router. When the PFE crashes and restarts, all active connections passing through that line card experience immediate interruption, potentially causing cascading failures in network services that depend on the affected router. Network administrators must consider the impact on service level agreements and customer-facing applications when planning mitigation strategies. The vulnerability affects multiple router models within the MX series, indicating a systemic issue within the Junos OS implementation rather than a localized problem. Organizations should implement immediate patch management procedures to address affected versions, with particular attention to the specific version thresholds mentioned in the vulnerability description. The memory leak behavior suggests that the vulnerability may be exploitable through automated tools that can generate and sustain the required frame streams, making it a potentially dangerous threat in environments where such tools are readily available. Security teams should monitor for potential exploitation attempts and implement network segmentation controls to limit the broadcast domain exposure where possible.