CVE-2020-1646 in Junos
Summary
by MITRE
On Juniper Networks Junos OS and Junos OS Evolved devices, processing a specific UPDATE for an EBGP peer can lead to a routing process daemon (RPD) crash and restart. This issue occurs only when the device is receiving and processing the BGP UPDATE for an EBGP peer. This issue does not occur when the device is receiving and processing the BGP UPDATE for an IBGP peer. However, the offending BGP UPDATE can originally come from an EBGP peer, propagates through the network via IBGP peers without causing crash, then it causes RPD crash when it is processed for a BGP UPDATE towards an EBGP peer. Repeated receipt and processing of the same specific BGP UPDATE can result in an extended Denial of Service (DoS) condition. This issue affects: Juniper Networks Junos OS: 17.3R3-S6, 17.4R2-S7, and 18.1R3-S7. Juniper Networks Junos OS Evolved 19.2R2-EVO and later versions, prior to 19.3R1-EVO. Other Junos OS releases are not affected.
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Analysis
by VulDB Data Team • 11/04/2020
This vulnerability represents a critical denial of service condition affecting Juniper Networks routing infrastructure through improper handling of specific BGP UPDATE messages. The flaw manifests in the routing process daemon (RPD) which is responsible for managing routing table updates and maintaining network connectivity. When processing a particular UPDATE message from an external border gateway protocol (EBGP) peer, the RPD experiences a crash and subsequent restart, disrupting network operations and potentially causing temporary routing black holes. The vulnerability specifically targets the processing logic within the RPD when it encounters certain malformed or specially crafted BGP UPDATE messages that contain specific attributes or path information patterns.
The technical implementation of this vulnerability stems from inadequate input validation within the BGP processing subsystem of Junos OS. The issue demonstrates characteristics consistent with CWE-129 Input Validation and CWE-20 Improper Input Validation, where the system fails to properly validate the structure and content of incoming BGP messages before processing them. When an EBGP peer sends an UPDATE message containing specific attribute combinations or path information that triggers an unexpected code path in the RPD, the daemon enters an unstable state leading to immediate termination. This behavior differs from normal IBGP processing where identical UPDATE messages do not cause the same destabilizing effect, indicating that the vulnerability is specifically related to how EBGP peer information is handled within the routing decision process.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise network stability and availability. Network operators experience immediate disruption when the RPD crashes and restarts, causing temporary loss of routing information and potential routing instability during the restart process. The vulnerability can be exploited through network propagation where an UPDATE message initially sent by an EBGP peer gets forwarded through IBGP peers without triggering the crash condition, but eventually reaches a destination where the same message causes the RPD to crash when processed for an EBGP peer. This propagation mechanism allows attackers to potentially cause extended denial of service conditions by repeatedly sending the same malicious UPDATE message, leading to continuous RPD restarts and prolonged network instability.
From an attack perspective, this vulnerability aligns with ATT&CK techniques related to service disruption and network denial of service. The flaw enables an attacker to potentially cause sustained network outages by repeatedly sending the specific BGP UPDATE message that triggers the RPD crash. The vulnerability affects specific versions of Junos OS including 17.3R3-S6, 17.4R2-S7, 18.1R3-S7, and certain Junos OS Evolved versions, with the potential for exploitation across these affected releases. The vulnerability demonstrates the importance of proper input validation in network protocol implementations and highlights the critical nature of maintaining secure routing daemon processes in enterprise networking infrastructure.
Mitigation strategies should focus on immediate patch application for affected Junos OS versions, implementing BGP UPDATE filtering mechanisms to prevent propagation of suspicious UPDATE messages, and monitoring for anomalous BGP UPDATE patterns. Network administrators should also consider implementing redundant routing paths and failover mechanisms to minimize the impact of potential exploitation. The vulnerability underscores the need for comprehensive testing of routing protocol implementations and proper input validation procedures to prevent similar issues in future deployments. Organizations should also implement monitoring solutions that can detect unusual RPD restart patterns and BGP UPDATE message anomalies that may indicate exploitation attempts.