CVE-2016-6401 in Carrier Routing System
Summary
by MITRE
Cisco Carrier Routing System (CRS) 5.1 and 5.1.4, as used in CRS Carrier Grade Services for CRS-1 and CRS-3 devices, allows remote attackers to cause a denial of service (line-card reload) via crafted IPv6-over-MPLS packets, aka Bug ID CSCva32494.
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Analysis
by VulDB Data Team • 09/19/2022
The vulnerability described in CVE-2016-6401 represents a critical denial of service flaw affecting Cisco Carrier Routing System implementations across CRS-1 and CRS-3 devices. This issue specifically manifests within the CRS Carrier Grade Services functionality where the system fails to properly handle crafted IPv6-over-MPLS packets, leading to unauthorized line-card reloads that effectively disrupt network services. The vulnerability impacts versions 5.1 and 5.1.4 of the CRS software, making it particularly concerning for large-scale network infrastructures that rely on these carrier-grade routing solutions for critical telecommunications services.
The technical flaw stems from insufficient input validation within the IPv6-over-MPLS packet processing pipeline of the affected Cisco CRS devices. When malformed or specially crafted IPv6-over-MPLS packets are transmitted to the system, the routing engine fails to properly validate the packet structure and content, resulting in a cascading failure that triggers an automatic line-card reload. This behavior represents a classic buffer over-read or improper state handling vulnerability where the system's failure to sanitize incoming packet data leads to an unexpected system state transition. The vulnerability operates at the network protocol level, specifically targeting the MPLS (Multiprotocol Label Switching) forwarding mechanism that is fundamental to carrier-grade routing operations.
The operational impact of this vulnerability extends beyond simple service disruption to encompass significant business continuity risks for telecommunications providers and network operators. When a line-card reload occurs, it results in temporary network outages that can affect thousands of connected services, potentially causing cascading failures across dependent systems. The remote exploitability of this vulnerability means that attackers can trigger the denial of service condition without requiring physical access or local network presence, making it particularly dangerous for publicly accessible network infrastructure. Network operators may experience extended downtime while system administrators work to restore services and investigate the incident, leading to potential revenue loss and customer service degradation.
Mitigation strategies for this vulnerability should prioritize immediate software patching through Cisco's security advisories, as the vendor has released updates specifically addressing the flawed packet handling logic. Network segmentation and access control measures should be implemented to limit exposure of affected CRS devices to untrusted network segments, while monitoring systems should be enhanced to detect anomalous packet patterns that may indicate exploitation attempts. Organizations should also consider implementing rate limiting and packet filtering rules at network boundaries to prevent malformed IPv6-over-MPLS traffic from reaching vulnerable devices. The vulnerability aligns with CWE-129, which covers improper validation of input, and falls under ATT&CK technique T1499.002 for network disruption attacks, highlighting the need for comprehensive network defense strategies that address both preventive and detective controls.