CVE-2019-0001 in Junos
Summary
by MITRE
Receipt of a malformed packet on MX Series devices with dynamic vlan configuration can trigger an uncontrolled recursion loop in the Broadband Edge subscriber management daemon (bbe-smgd), and lead to high CPU usage and a crash of the bbe-smgd service. Repeated receipt of the same packet can result in an extended denial of service condition for the device. Affected releases are Juniper Networks Junos OS: 16.1 versions prior to 16.1R7-S1; 16.2 versions prior to 16.2R2-S7; 17.1 versions prior to 17.1R2-S10, 17.1R3; 17.2 versions prior to 17.2R3; 17.3 versions prior to 17.3R3-S1; 17.4 versions prior to 17.4R2; 18.1 versions prior to 18.1R3; 18.2 versions prior to 18.2R2.
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Analysis
by VulDB Data Team • 07/01/2023
The vulnerability described in CVE-2019-0001 represents a critical software flaw within Juniper Networks MX Series routers that affects the broadband edge subscriber management daemon known as bbe-smgd. This daemon is responsible for managing dynamic vlan configurations in broadband edge environments where multiple subscribers connect through a single physical interface. The flaw manifests when the daemon processes malformed packets that contain recursive references or nested structures that exceed normal processing limits, creating an uncontrolled recursion loop within the service's execution flow. This issue specifically impacts devices running Junos OS versions prior to their respective security patches, with affected releases spanning multiple major versions from 16.1 through 18.2, indicating a widespread vulnerability across the product line.
The technical implementation of this vulnerability stems from inadequate input validation within the bbe-smgd daemon, which fails to properly sanitize or limit the depth of recursive packet processing. When malformed packets containing crafted data structures are received, the daemon enters a recursive processing loop where it continuously calls itself with increasingly complex parameters until system resources are exhausted. This behavior directly maps to CWE-674 - Uncontrolled Recursion, which specifically addresses scenarios where software fails to properly terminate recursive operations. The daemon's design does not include proper recursion depth limits or stack overflow protection mechanisms, allowing attackers to exploit this weakness through carefully constructed network traffic that triggers the problematic code path.
The operational impact of this vulnerability extends beyond simple service disruption to create sustained denial of service conditions that can severely impact network operations. Once triggered, the bbe-smgd service consumes excessive cpu cycles in the recursive loop, leading to complete service crashes that require manual intervention or device reboot to restore normal operation. Network administrators face the challenge of maintaining service availability when attackers can repeatedly send the same malformed packet to maintain the denial of service state, making this vulnerability particularly dangerous in production environments where network uptime is critical. The vulnerability affects dynamic vlan configurations specifically, which are commonly used in service provider networks where subscribers are dynamically assigned network resources based on their authentication and service provisioning status.
Mitigation strategies for CVE-2019-0001 require immediate deployment of security patches provided by Juniper Networks, specifically targeting the affected Junos OS versions mentioned in the advisory. Organizations should prioritize patching their MX Series devices to versions 16.1R7-S1, 16.2R2-S7, 17.1R2-S10, 17.1R3, 17.2R3, 17.3R3-S1, 17.4R2, 18.1R3, and 18.2R2 or later. Network administrators should implement traffic filtering rules to prevent malformed packets from reaching vulnerable devices, particularly focusing on ingress traffic that might contain crafted vlan headers or dynamic configuration requests. The vulnerability also aligns with ATT&CK technique T1499.004 - Endpoint Denial of Service, where adversaries leverage software flaws to exhaust system resources and cause service disruption. Additionally, implementing monitoring solutions to detect unusual cpu usage patterns in the bbe-smgd process can provide early warning of exploitation attempts, while network segmentation strategies can limit the scope of potential impact if the vulnerability is exploited in a multi-layered network architecture.