CVE-2021-1308 in Small Business RV Series Router
Summary
by MITRE • 04/08/2021
Multiple vulnerabilities exist in the Link Layer Discovery Protocol (LLDP) implementation for Cisco Small Business RV Series Routers. An unauthenticated, adjacent attacker could execute arbitrary code or cause an affected router to leak system memory or reload. A memory leak or device reload would cause a denial of service (DoS) condition on an affected device. For more information about these vulnerabilities, see the Details section of this advisory. Note: LLDP is a Layer 2 protocol. To exploit these vulnerabilities, an attacker must be in the same broadcast domain as the affected device (Layer 2 adjacent).
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Analysis
by VulDB Data Team • 04/11/2021
The vulnerability identified as CVE-2021-1308 represents a critical security flaw within the Link Layer Discovery Protocol implementation of Cisco Small Business RV Series Routers. This issue stems from improper handling of LLDP packets, which operates at Layer 2 of the OSI model and is designed to enable network devices to advertise their identity, configuration, and capabilities to neighboring devices. The vulnerability specifically affects the router's processing of LLDP frames, creating opportunities for exploitation that could result in severe operational impacts. According to the Common Weakness Enumeration framework, this vulnerability maps to CWE-121, which describes a weakness related to buffer overflow conditions in memory management, and potentially CWE-122, which addresses issues with buffer overflows that can lead to arbitrary code execution or system instability.
The technical exploitation of CVE-2021-1308 requires an attacker to be positioned within the same broadcast domain as the targeted router, making this a Layer 2 adjacent attack vector. This constraint significantly reduces the attack surface but does not eliminate the threat, particularly in environments where physical network access is possible or where attackers have achieved network positioning through other means. The vulnerability manifests through malformed LLDP packets that trigger memory corruption within the router's processing mechanisms, potentially leading to arbitrary code execution, memory leaks, or device reboots. The implementation flaw occurs during the parsing and handling of LLDP TLVs (Type-Length-Value) fields, where insufficient input validation allows attackers to craft packets that cause unexpected behavior in the router's operating system. This attack vector aligns with ATT&CK technique T1046, which covers network service scanning, and T1499, which addresses network disruption through resource exhaustion or system instability.
The operational impact of this vulnerability extends beyond simple denial of service conditions, as the potential for arbitrary code execution creates a pathway for attackers to gain persistent access to the affected network infrastructure. When a router experiences memory leaks due to these vulnerabilities, it can lead to gradual performance degradation and eventual system instability, while complete device reboots can cause network outages that affect business operations. The Cisco Small Business RV Series routers, commonly deployed in small office and home office environments, are particularly vulnerable because they often serve as the primary gateway device for network traffic, making their compromise potentially devastating to network availability. The vulnerability affects multiple models within the RV Series, including RV010, RV020, RV040, RV110W, RV120W, RV130W, and RV220W, with all affected devices sharing the same underlying LLDP implementation flaw. The attack scenario typically involves an attacker sending specially crafted LLDP packets to the router, which then processes these packets without proper validation, leading to the exploitation of memory handling errors. This vulnerability demonstrates the critical importance of proper input validation and memory management in network infrastructure devices, as even standard protocols like LLDP can become attack vectors when improperly implemented.
Organizations should implement immediate mitigations including disabling LLDP functionality on affected routers when not required, applying the latest firmware updates from Cisco, and implementing network segmentation to limit Layer 2 broadcast domains. Network administrators should also consider deploying intrusion detection systems that can monitor for anomalous LLDP packet patterns and implement access control lists to restrict LLDP traffic from untrusted network segments. The vulnerability highlights the need for robust network security practices that extend beyond traditional perimeter defenses, as Layer 2 attacks can bypass many conventional security controls. Additional defensive measures include monitoring for unusual router reboot patterns, implementing network access control to limit physical access to network infrastructure, and maintaining detailed network topology documentation to quickly identify and isolate affected devices. The broader implications of this vulnerability underscore the critical nature of firmware security in network infrastructure devices and the importance of regular security assessments to identify and remediate similar implementation flaws that could provide attackers with unauthorized access to critical network components.