CVE-2016-6467 in ASR 5000
Summary
by MITRE
A vulnerability in IPv6 packet fragment reassembly of StarOS for Cisco Aggregation Services Router (ASR) 5000 Series Switch could allow an unauthenticated, remote attacker to cause an unexpected reload of the Network Processing Unit (NPU) process. More Information: CSCva84552. Known Affected Releases: 20.0.0 21.0.0 21.0.M0.64702. Known Fixed Releases: 21.0.0 21.0.0.65256 21.0.M0.64970 21.0.V0.65150 21.1.A0.64973 21.1.PP0.65270 21.1.R0.65130 21.1.R0.65135 21.1.VC0.65203.
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Analysis
by VulDB Data Team • 10/05/2022
The vulnerability identified as CVE-2016-6467 represents a critical flaw in the IPv6 packet fragment reassembly functionality of Cisco's StarOS operating system running on the ASR 5000 Series Switch. This issue affects the Network Processing Unit's ability to properly handle fragmented IPv6 packets, creating a potential vector for remote exploitation without requiring authentication credentials. The vulnerability stems from improper handling of packet fragmentation sequences during the reassembly process, which can lead to memory corruption or process instability within the NPU subsystem.
The technical implementation of this vulnerability occurs during the IPv6 fragment reassembly process where the StarOS software fails to properly validate or process fragmented packet data. When an attacker sends specifically crafted IPv6 packets with overlapping or malformed fragment offsets, the NPU process becomes unable to correctly reconstruct the original packet. This mismanagement results in a critical error condition that triggers an unexpected reload of the NPU process, effectively causing a service disruption. The flaw operates at the network protocol level and specifically targets the IPv6 implementation within the router's forwarding engine, making it particularly dangerous for network infrastructure devices.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise network availability and reliability. An unauthenticated remote attacker can exploit this weakness to repeatedly trigger NPU reloads, leading to denial of service conditions that can persist until manual intervention occurs. The vulnerability affects multiple software releases including versions 20.0.0 and 21.0.0, with specific patches available in release versions 21.0.0.65256 and later. Network administrators must understand that this issue can be exploited without any prior authentication, making it particularly concerning for publicly accessible network devices. The potential for repeated exploitation means that a single attack can cause sustained network degradation or complete service outages.
Cisco has addressed this vulnerability through multiple software release updates, with fixed versions available starting from 21.0.0.65256 and subsequent releases. Organizations should prioritize applying these patches to their ASR 5000 Series devices to eliminate the risk of exploitation. The mitigation strategy involves not only applying the official software updates but also implementing network segmentation and monitoring to detect unusual packet fragmentation patterns that might indicate attempted exploitation. Network security teams should consider implementing intrusion detection systems that can identify malformed IPv6 fragments and monitor NPU process restart events as potential indicators of this vulnerability being targeted. This vulnerability aligns with CWE-129 and CWE-131 categories related to improper input validation and buffer overflow conditions, and represents a potential technique in the ATT&CK framework under network infiltration and denial of service attack vectors. Organizations should also consider implementing rate limiting for fragment reassembly operations and maintaining detailed logging of NPU process behavior to facilitate early detection of exploitation attempts.