CVE-2020-1656 in Junos
Summary
by MITRE • 10/17/2020
The DHCPv6 Relay-Agent service, part of the Juniper Enhanced jdhcpd daemon shipped with Juniper Networks Junos OS has an Improper Input Validation vulnerability which will result in a Denial of Service (DoS) condition when a DHCPv6 client sends a specific DHPCv6 message allowing an attacker to potentially perform a Remote Code Execution (RCE) attack on the target device. Continuous receipt of the specific DHCPv6 client message will result in an extended Denial of Service (DoS) condition. If adjacent devices are also configured to relay DHCP packets, and are not affected by this issue and simply transparently forward unprocessed client DHCPv6 messages, then the attack vector can be a Network-based attack, instead of an Adjacent-device attack. No other DHCP services are affected. Receipt of the packet without configuration of the DHCPv6 Relay-Agent service, will not result in exploitability of this issue. This issue affects Juniper Networks Junos OS: 12.3 versions prior to 12.3R12-S15; 12.3X48 versions prior to 12.3X48-D95; 14.1X53 versions prior to 14.1X53-D53; 15.1 versions prior to 15.1R7-S6; 15.1X49 versions prior to 15.1X49-D200; 15.1X53 versions prior to 15.1X53-D593; 16.1 versions prior to 16.1R7-S7; 16.2 versions prior to 16.2R2-S11; 17.1 versions prior to 17.1R2-S11, 17.1R3-S2; 17.2 versions prior to 17.2R3-S3; 17.2X75 versions prior to 17.2X75-D44; 17.3 versions prior to 17.3R3-S7; 17.4 versions prior to 17.4R2-S9, 17.4R3; 18.1 versions prior to 18.1R3-S9; 18.2 versions prior to 18.2R2-S6, 18.2R3-S2; 18.2X75 versions prior to 18.2X75-D12, 18.2X75-D33, 18.2X75-D435, 18.2X75-D60; 18.3 versions prior to 18.3R1-S7, 18.3R2-S3, 18.3R3-S1; 18.4 versions prior to 18.4R1-S5, 18.4R2-S3, 18.4R3; 19.1 versions prior to 19.1R1-S4, 19.1R2; 19.2 versions prior to 19.2R1-S3, 19.2R2; 19.3 versions prior to 19.3R2.
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Analysis
by VulDB Data Team • 11/20/2020
The vulnerability identified as CVE-2020-1656 represents a critical improper input validation flaw within the DHCPv6 Relay-Agent service of Juniper Networks Junos OS operating systems. This weakness exists within the enhanced jdhcpd daemon implementation and manifests as a denial of service condition when specifically crafted DHCPv6 client messages are transmitted to affected devices. The technical nature of this vulnerability places it squarely within the scope of CWE-20, which defines improper input validation as a fundamental security weakness that can lead to various attack vectors including remote code execution. The vulnerability operates through a classic buffer overflow or memory corruption mechanism where malformed input validation fails to properly sanitize incoming DHCPv6 packets, creating potential entry points for malicious actors.
The operational impact of this vulnerability extends beyond simple service disruption to potentially enable remote code execution attacks when properly crafted malicious packets are continuously transmitted to vulnerable systems. The attack requires an adversary to send specific DHCPv6 messages to devices configured with the DHCPv6 Relay-Agent service, making this a network-based attack vector when adjacent devices are not affected and simply forward unprocessed packets. This characteristic transforms the attack from requiring physical adjacency to potentially remote exploitation, significantly expanding the threat surface. The DoS condition can be sustained through continuous receipt of the malicious DHCPv6 messages, creating extended disruption periods that can severely impact network infrastructure availability and service continuity.
Security practitioners should recognize this vulnerability through the ATT&CK framework's T1499.004 technique, which covers network denial of service attacks targeting network infrastructure devices. The affected Junos OS versions span multiple major releases including 12.3, 14.1, 15.1, 16.1, 16.2, 17.1, 17.2, 17.3, 17.4, 18.1, 18.2, 18.3, 18.4, 19.1, 19.2, and 19.3, indicating a widespread exposure across the Juniper Networks product line. The vulnerability specifically targets devices configured with DHCPv6 Relay-Agent services, meaning that simple receipt of DHCPv6 packets without this service enabled does not create exploitability conditions. This selective impact requires security teams to identify and remediate only specific device configurations rather than implementing broad network-wide mitigations.
Mitigation strategies should prioritize immediate patch deployment to all affected Junos OS versions, with particular attention to the specific release thresholds mentioned in the vulnerability advisory. Network segmentation and access control measures can provide additional defense-in-depth layers by limiting which devices can receive and process DHCPv6 messages, thereby reducing the potential attack surface. Implementing DHCPv6 message filtering and validation at network boundaries can help detect and block malicious packets before they reach vulnerable devices. Security monitoring should focus on unusual DHCPv6 traffic patterns and continuous DoS conditions that may indicate exploitation attempts. The remediation process should also include comprehensive network inventory assessments to identify all devices running affected Junos OS versions and ensure complete coverage of the vulnerability remediation efforts.