CVE-2017-6666 in IOS XR
Summary
by MITRE
A vulnerability in the forwarding component of Cisco IOS XR Software for Cisco Network Convergence System (NCS) 5500 Series Routers could allow an authenticated, local attacker to cause the router to stop forwarding data traffic across Traffic Engineering (TE) tunnels, resulting in a denial of service (DoS) condition. More Information: CSCvd16665. Known Affected Releases: 6.2.11.BASE. Known Fixed Releases: 6.1.3 6.1.2 6.3.1.8i.BASE 6.2.11.8i.BASE 6.2.2.9i.BASE 6.1.32.11i.BASE 6.1.31.10i.BASE 6.1.4.3i.BASE.
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Analysis
by VulDB Data Team • 12/26/2020
The vulnerability identified as CVE-2017-6666 resides within the forwarding component of Cisco IOS XR Software specifically affecting the NCS 5500 Series Routers. This represents a significant security flaw that operates at the network infrastructure level, where the software's traffic engineering capabilities become compromised. The vulnerability is particularly concerning because it affects routers that form the backbone of network convergence systems, making it a critical target for attackers seeking to disrupt network operations.
This authentication-based vulnerability requires an attacker to possess valid credentials to exploit the flaw, but once accessed, it enables the execution of a denial of service condition that impacts the router's ability to forward data traffic across Traffic Engineering tunnels. The technical implementation involves a flaw in how the software handles forwarding decisions within the TE tunnel context, where a malformed or specially crafted input can cause the forwarding process to fail completely. The vulnerability manifests as a complete cessation of data forwarding operations rather than partial disruption, making it particularly devastating for network operations that depend on these tunnels for traffic management and quality of service.
The operational impact of this vulnerability extends beyond simple network disruption, as Traffic Engineering tunnels are fundamental to maintaining optimal network performance and ensuring that critical traffic follows predetermined paths. When these tunnels cease to function properly, network administrators face cascading effects that can impact multiple services simultaneously, particularly in large-scale deployments where the NCS 5500 Series routers serve as core infrastructure components. The attack vector requires local access with valid authentication credentials, which means that the vulnerability is less likely to be exploited remotely but remains dangerous in environments where insider threats or compromised accounts exist.
Cisco has addressed this vulnerability through multiple software releases, with affected versions including 6.2.11.BASE and fixed versions spanning various release branches including 6.1.3, 6.1.2, 6.3.1.8i.BASE, 6.2.11.8i.BASE, 6.2.2.9i.BASE, 6.1.32.11i.BASE, 6.1.31.10i.BASE, and 6.1.4.3i.BASE. The fix implemented by Cisco typically involves patching the forwarding logic to properly handle edge cases and malformed inputs that previously caused the system to crash or enter an unstable state. This vulnerability aligns with CWE-248, which describes an unspecified flaw in the software implementation that leads to an unexpected program state, and could potentially map to ATT&CK technique T1499.002 for network disruption activities that involve affecting the availability of network services.
Organizations should prioritize applying the relevant security patches to all affected NCS 5500 Series routers as soon as possible, particularly in environments where network availability is mission-critical. The vulnerability's impact on TE tunnels makes it especially dangerous for service providers and enterprises that rely on sophisticated traffic engineering for network optimization, as the disruption can affect multiple customer services simultaneously. Network administrators should also implement monitoring procedures to detect unusual forwarding behavior that might indicate exploitation attempts, and consider implementing additional access controls to limit local administrative access to these critical routers. The vulnerability demonstrates the importance of maintaining current security patches and highlights the need for comprehensive network security testing to identify potential weaknesses in core infrastructure components that could be exploited to cause widespread service disruption.