CVE-2020-3398 in NX-OS
Summary
by MITRE
A vulnerability in the Border Gateway Protocol (BGP) Multicast VPN (MVPN) implementation of Cisco NX-OS Software could allow an unauthenticated, remote attacker to cause a BGP session to repeatedly reset, causing a partial denial of service (DoS) condition due to the BGP session being down. The vulnerability is due to incorrect parsing of a specific type of BGP MVPN update message. An attacker could exploit this vulnerability by sending this BGP MVPN update message to a targeted device. A successful exploit could allow the attacker to cause the BGP peer connections to reset, which could lead to BGP route instability and impact traffic. The incoming BGP MVPN update message is valid but is parsed incorrectly by the NX-OS device, which could send a corrupted BGP update to the configured BGP peer. Note: The Cisco implementation of BGP accepts incoming BGP traffic from only explicitly configured peers. To exploit this vulnerability, an attacker must send a specific BGP MVPN update message over an established TCP connection that appears to come from a trusted BGP peer. To do so, the attacker must obtain information about the BGP peers in the trusted network of the affected system.
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Analysis
by VulDB Data Team • 11/11/2020
The vulnerability identified as CVE-2020-3398 resides within the Border Gateway Protocol Multicast VPN implementation of Cisco NX-OS Software, representing a critical security flaw that compromises the stability and availability of network infrastructure. This issue manifests as a partial denial of service condition where BGP sessions experience repeated resets, disrupting network operations and potentially causing significant traffic disruption. The vulnerability stems from improper parsing mechanisms within the software's handling of specific BGP MVPN update messages, creating a scenario where legitimate network traffic can be exploited to cause operational degradation.
The technical flaw operates through a specific parsing error that occurs when the NX-OS device processes incoming BGP MVPN update messages. When such a message is received, the system incorrectly interprets the message structure, leading to the generation of corrupted BGP update packets that are then transmitted to configured BGP peers. This malformed packet processing creates a cascading effect where BGP peer connections repeatedly reset, resulting in route instability and potential traffic blackholing. The vulnerability is particularly concerning because it requires minimal privileges for exploitation, as the attacker does not need authentication credentials to initiate the attack.
From an operational impact perspective, this vulnerability creates significant disruption to network services by causing BGP session instability and route flapping. The repeated session resets can lead to network convergence issues, where routing tables continuously update and stabilize, causing temporary network outages and performance degradation. The attack vector requires an attacker to establish a TCP connection that appears to originate from a trusted BGP peer, making this vulnerability particularly dangerous in environments where network trust relationships are established. The exploitation process involves sending a valid but malformed BGP MVPN update message, which bypasses traditional authentication mechanisms while still triggering the parsing error.
The vulnerability aligns with CWE-129, which addresses improper validation of input boundaries, and reflects common patterns in network protocol implementations where input validation fails to properly handle edge cases in message parsing. From an ATT&CK framework perspective, this vulnerability maps to T1059.001 for command and scripting interpreter and T1498.001 for network denial of service, as it enables an attacker to disrupt network services through protocol manipulation. The attack requires knowledge of the target network's BGP peer configuration, making it more challenging to exploit but still feasible in environments where network topology information is accessible. Network administrators must understand that this vulnerability affects the core routing protocols that maintain network connectivity, making it a critical concern for network infrastructure security.
Mitigation strategies should focus on implementing proper input validation and boundary checking mechanisms within the BGP implementation, along with network segmentation and access control measures to limit exposure. The affected Cisco NX-OS devices should be updated with patches provided by Cisco that address the specific parsing error in MVPN update message handling. Network monitoring should be enhanced to detect unusual BGP session reset patterns and route flapping behavior. Additionally, implementing BGP session authentication and filtering mechanisms can help reduce the attack surface by limiting which external peers can establish connections to internal routing infrastructure. Organizations should also consider implementing network intrusion detection systems that can identify and alert on suspicious BGP update message patterns that may indicate exploitation attempts.