CVE-2015-0718 in NX-OS
Summary
by MITRE
Cisco NX-OS 4.0 through 6.1 on Nexus 1000V 3000, 4000, 5000, 6000, and 7000 devices and Unified Computing System (UCS) platforms allows remote attackers to cause a denial of service (TCP stack reload) by sending crafted TCP packets to a device that has a TIME_WAIT TCP session, aka Bug ID CSCub70579.
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Analysis
by VulDB Data Team • 07/08/2022
The vulnerability described in CVE-2015-0718 represents a critical denial of service flaw affecting Cisco NX-OS software versions 4.0 through 6.1 across multiple Nexus and UCS platforms. This weakness specifically targets the TCP stack implementation within Cisco's networking infrastructure, creating a condition where legitimate network services can be disrupted through carefully crafted network traffic. The vulnerability operates within the context of established network protocols and TCP connection states, making it particularly dangerous as it can be exploited without requiring authentication or privileged access. The affected platforms include Nexus 1000V virtual switches across multiple series and Unified Computing System platforms, indicating the widespread nature of this vulnerability across Cisco's enterprise networking portfolio.
The technical flaw manifests when a device maintains a TCP session in the TIME_WAIT state and receives specially crafted TCP packets that trigger an unintended reload of the TCP stack. This condition falls under CWE-121, which describes heap-based buffer overflow conditions, though the specific mechanism involves TCP stack state management rather than traditional buffer overflows. The vulnerability exploits the timing and sequence of TCP packet handling within the network infrastructure, specifically targeting the state transition mechanisms that occur during TCP session termination. When the malicious packets are received during a TIME_WAIT session, they cause the system to reload its TCP stack components, effectively disrupting network connectivity and service availability for the affected device. The exploitation requires minimal network access and can be performed remotely, making it particularly dangerous in production environments where network availability is critical.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise entire network segments that rely on affected Cisco devices. When the TCP stack reload occurs, it can result in complete loss of connectivity for the affected device, forcing network administrators to manually intervene to restore services. The TIME_WAIT state is a standard TCP connection state that occurs after a connection is closed, typically lasting for a period of time to ensure all packets are properly handled. However, the vulnerability exploits this legitimate state to cause system instability, demonstrating a sophisticated understanding of TCP protocol behavior. Network administrators may experience unexpected downtime, service interruptions, and potential cascading failures throughout the network infrastructure, as affected devices may become unreachable and require manual intervention to restore normal operations. The vulnerability's impact is particularly severe in data center environments where UCS platforms and Nexus switches form the backbone of network connectivity.
Mitigation strategies for CVE-2015-0718 should focus on immediate software updates and network segmentation to prevent exploitation. Cisco released patches addressing this vulnerability in subsequent software releases, and organizations should prioritize applying these updates to all affected devices. The vulnerability aligns with ATT&CK technique T1499.004, which covers network disruption through TCP stack manipulation, indicating that threat actors could potentially use this weakness to create targeted network outages. Network administrators should implement monitoring solutions to detect unusual TCP packet patterns that might indicate exploitation attempts, and consider temporary network isolation of affected devices until patches are deployed. Additionally, implementing rate limiting and TCP stack hardening measures can help reduce the attack surface and provide additional protection against similar vulnerabilities. The remediation process should include comprehensive testing of patches in controlled environments before deployment to production networks, ensuring that updates do not introduce compatibility issues with existing network configurations and services.