CVE-2020-3338 in NX-OS
Summary
by MITRE
A vulnerability in the Protocol Independent Multicast (PIM) feature for IPv6 networks (PIM6) of Cisco NX-OS Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. The vulnerability is due to improper error handling when processing inbound PIM6 packets. An attacker could exploit this vulnerability by sending multiple crafted PIM6 packets to an affected device. A successful exploit could allow the attacker to cause the PIM6 application to leak system memory. Over time, this memory leak could cause the PIM6 application to stop processing legitimate PIM6 traffic, leading to a DoS condition on the affected device.
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Analysis
by VulDB Data Team • 11/11/2020
The vulnerability identified as CVE-2020-3338 resides within the Protocol Independent Multicast version 6 (PIM6) implementation of Cisco NX-OS Software, representing a critical security flaw that compromises network availability through deliberate resource exhaustion. This weakness specifically targets the handling of inbound PIM6 packets within the multicast routing infrastructure, creating a pathway for remote attackers to manipulate system resources without requiring authentication credentials. The flaw manifests in the improper error handling mechanisms that govern how the software processes malformed or specially crafted multicast packets, exposing the underlying system to sustained exploitation attempts that gradually degrade operational performance.
The technical exploitation of this vulnerability leverages the memory management deficiencies inherent in the PIM6 application layer, where each crafted packet triggers an insufficient error response that results in progressive memory allocation without proper cleanup. This memory leak behavior accumulates over time, with each successful packet transmission contributing to the gradual depletion of available system resources. The vulnerability's impact extends beyond simple resource exhaustion as the progressive memory consumption eventually leads to application instability and complete service disruption, effectively rendering the affected device incapable of processing legitimate multicast traffic. The attack vector requires only the transmission of multiple specially formatted PIM6 packets to an affected device, making it particularly dangerous as it can be executed remotely without requiring physical access or advanced privileges.
From an operational standpoint, this vulnerability presents a significant threat to network infrastructure reliability and availability, particularly in environments where multicast routing is essential for data distribution and network performance optimization. The DoS condition created by this flaw can impact critical network services that depend on PIM6 functionality, potentially affecting large-scale deployments including enterprise networks, data centers, and service provider infrastructures. The gradual nature of the memory leak means that detection may be delayed, allowing attackers to maintain persistent disruption without immediate notice, while the cumulative effect can cause complete service failure that requires manual intervention and system restarts to restore normal operations.
Organizations should implement immediate mitigations including network segmentation to isolate affected devices, deployment of access control lists to filter suspicious PIM6 traffic, and application of Cisco's official security patches to address the root cause. The vulnerability aligns with CWE-457, which addresses the use of uninitialized variables and improper error handling in software systems, while also mapping to ATT&CK technique T1499.004 for network denial of service attacks. Network administrators should monitor affected systems for signs of memory consumption anomalies and implement comprehensive logging to track PIM6 packet processing activities. The remediation process requires careful consideration of the patch deployment timeline to avoid service disruption while ensuring complete vulnerability resolution across all network devices running affected NX-OS versions.