CVE-2019-0063 in Junos
Summary
by MITRE
When an MX Series Broadband Remote Access Server (BRAS) is configured as a Broadband Network Gateway (BNG) with DHCPv6 enabled, jdhcpd might crash when receiving a specific crafted DHCP response message on a subscriber interface. The daemon automatically restarts without intervention, but continuous receipt of specific crafted DHCP messages will repeatedly crash jdhcpd, leading to an extended Denial of Service (DoS) condition. This issue only affects systems configured with DHCPv6 enabled. DHCPv4 is unaffected by this issue. This issue affects Juniper Networks Junos OS: 15.1 versions prior to 15.1R7-S5 on MX Series; 16.1 versions prior to 16.1R7-S5 on MX Series; 16.2 versions prior to 16.2R2-S10 on MX Series; 17.1 versions prior to 17.1R3-S1 on MX Series; 17.2 versions prior to 17.2R3-S2 on MX Series; 17.3 versions prior to 17.3R3-S6 on MX Series; 17.4 versions prior to 17.4R2-S5, 17.4R3 on MX Series; 18.1 versions prior to 18.1R3-S6 on MX Series; 18.2 versions prior to 18.2R2-S4, 18.2R3 on MX Series; 18.2X75 versions prior to 18.2X75-D50 on MX Series; 18.3 versions prior to 18.3R1-S5, 18.3R3 on MX Series; 18.4 versions prior to 18.4R2 on MX Series; 19.1 versions prior to 19.1R1-S2, 19.1R2 on MX Series.
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Analysis
by VulDB Data Team • 01/05/2024
The vulnerability identified as CVE-2019-0063 represents a critical denial of service weakness in Juniper Networks MX Series Broadband Remote Access Servers operating as Broadband Network Gateways with DHCPv6 functionality enabled. This issue specifically targets the jdhcpd daemon responsible for handling dynamic host configuration protocol version 6 communications within the network infrastructure. The flaw manifests when the daemon processes specially crafted DHCP response messages that are transmitted to subscriber interfaces, causing the service to terminate unexpectedly and automatically restart without requiring administrator intervention. This behavior creates a cascading effect where repeated exploitation can maintain sustained denial of service conditions, effectively disrupting network connectivity for subscribers connected through the affected BRAS devices.
The technical nature of this vulnerability stems from inadequate input validation within the jdhcpd daemon implementation, which fails to properly handle malformed or maliciously constructed DHCPv6 response messages. This weakness aligns with common software security principles where insufficient sanitization of user-supplied data leads to application instability and potential system compromise. The vulnerability specifically affects systems configured with DHCPv6 enabled while maintaining unaffected status for DHCPv4 implementations, indicating a protocol-specific flaw within the IPv6 handling components of the Junos OS. The attack vector requires network access to the subscriber interface and the ability to craft specific DHCP messages that trigger the daemon crash, making it a remote exploit that can be leveraged by attackers with network access to the affected infrastructure.
From an operational impact perspective, this vulnerability poses significant risks to network service availability and subscriber connectivity. The automatic restart mechanism of jdhcpd creates a false sense of security since the service appears to recover, but the repeated crashes indicate a persistent threat that can be sustained over time. Network administrators face the challenge of maintaining service availability while the daemon continuously restarts, potentially leading to extended periods of service degradation or complete loss of subscriber connectivity. The vulnerability affects multiple Junos OS versions across different release series, indicating a widespread impact that requires coordinated patch management across various network deployments. This issue particularly affects service providers who rely on MX Series equipment for broadband access services, as it directly impacts their ability to maintain reliable subscriber connections and network operations.
The mitigation strategies for CVE-2019-0063 primarily involve applying the appropriate software patches released by Juniper Networks to address the specific daemon crash vulnerability. Network administrators should prioritize upgrading affected systems to versions that contain the necessary fixes, with particular attention to the specific version requirements outlined in the vulnerability description. Additionally, implementing network segmentation and access controls to limit the ability of unauthorized parties to send crafted DHCP messages to subscriber interfaces provides an additional layer of protection. Monitoring systems should be configured to detect unusual patterns of daemon restarts or DHCP traffic anomalies that could indicate exploitation attempts. Security teams should also consider implementing network intrusion detection systems that can identify and alert on suspicious DHCP message patterns. The vulnerability's classification aligns with CWE-129 and CWE-20 categories related to input validation and improper handling of potentially malicious data, while the operational impact reflects ATT&CK technique T1499.004 for network disruption and service availability compromise. Organizations should also review their network access controls and implement proper network segmentation to reduce the attack surface and limit potential exploitation vectors.