CVE-2017-6633 in UCS C-Series Rack Servers
Summary
by MITRE
A vulnerability in the TCP throttling process of Cisco UCS C-Series Rack Servers 3.0(0.234) could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. The vulnerability is due to insufficient rate-limiting protection. An attacker could exploit this vulnerability by sending a high rate of TCP SYN packets to a specific TCP listening port on an affected device. An exploit could allow the attacker to cause a specific TCP listening port to stop accepting new connections, resulting in a DoS condition. Cisco Bug IDs: CSCva65544.
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Analysis
by VulDB Data Team • 12/25/2020
The vulnerability identified as CVE-2017-6633 resides within the TCP throttling mechanism of Cisco UCS C-Series Rack Servers running firmware version 3.0(0.234). This weakness represents a critical security flaw that undermines the network resilience of affected systems by failing to implement adequate rate-limiting controls. The vulnerability specifically targets the TCP SYN packet handling process, which forms the foundation of the three-way handshake mechanism used to establish TCP connections. When an attacker exploits this flaw, they can overwhelm the targeted device's TCP listening port with an excessive volume of SYN packets, effectively exhausting system resources and disrupting normal network operations. The root cause of this vulnerability stems from insufficient protective measures within the TCP throttling process, leaving the system vulnerable to exploitation without requiring any authentication credentials. This characteristic makes the vulnerability particularly dangerous as it can be exploited remotely by any attacker with network access to the affected device.
The operational impact of CVE-2017-6633 manifests as a denial of service condition that specifically targets TCP listening ports on the affected Cisco UCS C-Series servers. When exploited, the vulnerability causes a targeted TCP port to cease accepting new connections, effectively rendering services unavailable to legitimate users. The attack vector involves sending a high-rate stream of TCP SYN packets to a specific listening port, which triggers the system's inability to properly manage connection requests. This DoS condition can persist until the affected system is manually restarted or the excessive traffic ceases, potentially causing significant operational disruption for organizations relying on these servers for critical infrastructure services. The vulnerability's exploitation does not require authentication, making it accessible to any remote attacker who can reach the target device over the network. The Cisco bug ID CSCva65544 documents this specific weakness within the vendor's internal tracking system, confirming the legitimate nature of the reported vulnerability.
Security professionals should recognize this vulnerability as a manifestation of inadequate network protocol implementation and resource management within the TCP stack of affected Cisco devices. The flaw aligns with common weakness enumerations such as CWE-770, which addresses allocation of resources without proper limits, and CWE-400, which covers unspecified resource exhaustion. From an adversarial perspective, this vulnerability maps to ATT&CK technique T1499.004, specifically targeting network denial of service conditions through resource exhaustion attacks. Organizations should implement immediate mitigations including network-level rate limiting, firewall rules to restrict SYN packet rates, and monitoring for unusual traffic patterns on TCP listening ports. The vulnerability demonstrates the critical importance of proper TCP throttling mechanisms in preventing resource exhaustion attacks and maintaining system availability. Additionally, this flaw highlights the necessity of regular firmware updates and proactive security assessments to identify and remediate similar weaknesses in network infrastructure components. Cisco has addressed this vulnerability through firmware updates that enhance the TCP throttling mechanisms and provide more robust protection against excessive SYN packet flooding attacks.