CVE-2021-0211 in Junos
Summary
by MITRE • 01/16/2021
An improper check for unusual or exceptional conditions in Juniper Networks Junos OS and Junos OS Evolved Routing Protocol Daemon (RPD) service allows an attacker to send a valid BGP FlowSpec message thereby causing an unexpected change in the route advertisements within the BGP FlowSpec domain leading to disruptions in network traffic causing a Denial of Service (DoS) condition. Continued receipt of these update messages will cause a sustained Denial of Service condition. This issue affects Juniper Networks: Junos OS: All versions prior to 17.3R3-S10 with the exceptions of 15.1X49-D240 on SRX Series and 15.1R7-S8 on EX Series; 17.3 versions prior to 17.3R3-S10; 17.4 versions prior to 17.4R2-S12, 17.4R3-S4; 18.1 versions prior to 18.1R3-S12; 18.2 versions prior to 18.2R2-S8, 18.2R3-S6; 18.3 versions prior to 18.3R3-S4; 18.4 versions prior to 18.4R1-S8, 18.4R2-S6, 18.4R3-S6; 19.1 versions prior to 19.1R1-S6, 19.1R2-S2, 19.1R3-S3; 19.2 versions prior to 19.2R3-S1; 19.3 versions prior to 19.3R2-S5, 19.3R3-S1; 19.4 versions prior to 19.4R1-S3, 19.4R2-S3, 19.4R3; 20.1 versions prior to 20.1R2; 20.2 versions prior to 20.2R1-S3 20.2R2; 20.3 versions prior to 20.3R1-S1, 20.3R2. Junos OS Evolved: All versions prior to 20.3R1-S1-EVO, 20.3R2-EVO.
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Analysis
by VulDB Data Team • 02/14/2021
This vulnerability represents a critical flaw in the BGP FlowSpec implementation within Juniper Networks Junos OS and Junos OS Evolved routing protocol daemon services. The issue stems from an insufficient validation mechanism that fails to properly check for unusual or exceptional conditions when processing BGP FlowSpec messages. This weakness allows malicious actors to craft and transmit valid BGP FlowSpec updates that trigger unexpected modifications to route advertisements within the BGP FlowSpec domain. The vulnerability specifically targets the routing protocol daemon service which is responsible for managing and propagating routing information across network infrastructure. According to the CWE classification, this represents a weakness in the validation of input data or exceptional conditions, falling under CWE-252 Improper Check for Unusual or Exceptional Conditions. The flaw exists in the RPD service's handling of FlowSpec messages, which are used for traffic filtering and policy enforcement in BGP networks. The security implications are significant as BGP FlowSpec functionality is commonly deployed in production networks for traffic control and security policy enforcement. When exploited, this vulnerability can cause immediate disruption to network traffic flows, as the malformed FlowSpec messages trigger unexpected route modifications that can cascade through the network's routing tables.
The technical exploitation of this vulnerability occurs through the careful crafting of BGP FlowSpec messages that bypass normal validation checks within the routing protocol daemon. Attackers can send these specially constructed messages to affected Junos OS systems, causing the RPD service to process them incorrectly and subsequently modify route advertisements in ways that disrupt normal network operations. The vulnerability manifests as a denial of service condition where legitimate traffic flow is disrupted due to incorrect route handling. The specific nature of the flaw suggests that the system fails to properly validate the structure or content of FlowSpec messages, allowing malformed data to be processed without adequate error handling or sanitization. This improper validation creates a condition where the routing daemon becomes unstable or enters an unexpected state when processing these messages. The attack vector is particularly concerning because BGP FlowSpec messages are legitimate network control plane communications that are expected to be processed by routing daemons. This means that the attack can be executed using standard BGP protocol mechanisms without requiring special privileges or unusual network access. The vulnerability is particularly dangerous in production environments where BGP FlowSpec is actively deployed for traffic management and security policy enforcement.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise network stability and availability. When an attacker successfully exploits this flaw, they can cause sustained denial of service conditions that persist as long as malicious FlowSpec messages continue to be received by the affected system. This can result in complete disruption of network services, as route advertisements become corrupted or modified in ways that prevent proper routing decisions. The affected systems may experience routing instability, where legitimate routes are overridden or corrupted by the malicious FlowSpec updates. This can lead to traffic blackholing, where packets are dropped due to incorrect routing decisions, or traffic redirection that causes network congestion. The vulnerability affects multiple versions of Junos OS across different release series, indicating a widespread issue that impacts various network infrastructure deployments. The sustained nature of the denial of service means that network administrators must take immediate action to prevent ongoing disruption to their services, as the impact can persist until the vulnerability is patched or mitigated through other means. The widespread version impact suggests that this vulnerability has been present in the codebase for an extended period, making it a persistent threat to network infrastructure.
Mitigation strategies for this vulnerability must address both immediate protection and long-term remediation. The primary recommendation is to apply the vendor-provided security patches and updates that address the specific validation flaw in the RPD service's handling of BGP FlowSpec messages. Organizations should prioritize patching affected systems, particularly those running versions prior to the specified secure releases. Network administrators should implement monitoring and detection mechanisms to identify potentially malicious FlowSpec messages that could trigger this vulnerability. The implementation of BGP FlowSpec message filtering and validation at network boundaries can provide additional protection against exploitation attempts. Organizations should also consider disabling BGP FlowSpec functionality if it is not actively required for their network operations, as this eliminates the attack surface entirely. According to ATT&CK framework methodology, this vulnerability aligns with techniques involving privilege escalation and denial of service through protocol manipulation. Network segmentation and access control measures can help limit the potential impact of exploitation by restricting which systems can receive and process BGP FlowSpec messages. Regular security assessments and vulnerability scanning should be conducted to identify any remaining affected systems that may have been overlooked during initial patching efforts. The vulnerability also highlights the importance of proper input validation and error handling in network protocol implementations, as recommended by industry security best practices and standards such as those defined in the NIST Cybersecurity Framework and ISO/IEC 27001 security management standards.