CVE-2025-20191 in NX-OS
Summary
by MITRE • 05/07/2025
A vulnerability in the Switch Integrated Security Features (SISF) of Cisco IOS Software, Cisco IOS XE Software, Cisco NX-OS Software, and Cisco Wireless LAN Controller (WLC) AireOS Software could allow an unauthenticated, adjacent attacker to cause a denial of service (DoS) condition on an affected device.
This vulnerability is due to the incorrect handling of DHCPv6 packets. An attacker could exploit this vulnerability by sending a crafted DHCPv6 packet to an affected device. A successful exploit could allow the attacker to cause the device to reload, resulting in a DoS condition.
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Analysis
by VulDB Data Team • 05/08/2025
This vulnerability resides within Cisco's Switch Integrated Security Features implementation across multiple software platforms including IOS Software, IOS XE Software, NX-OS Software, and Wireless LAN Controller AireOS Software. The flaw represents a critical denial of service weakness that specifically targets the processing of DHCPv6 packets, demonstrating how fundamental network protocol handling can lead to system-wide operational failures. The vulnerability affects devices that are typically deployed in enterprise environments where network availability and reliability are paramount, making this a significant concern for organizations relying on Cisco networking infrastructure. The impact extends beyond simple service interruption as the device reload required to recover from this condition can result in extended network downtime and potential cascading failures in dependent systems.
The technical root cause stems from improper input validation and handling of DHCPv6 packet structures within the affected software implementations. When an attacker crafts and transmits a maliciously formatted DHCPv6 packet to an affected device, the system fails to properly process the malformed packet and instead triggers an internal error condition that leads to system reload. This represents a classic buffer over-read or improper state handling vulnerability where the software does not adequately validate packet contents before processing. The vulnerability specifically manifests when the device encounters DHCPv6 packets that contain unexpected or malformed fields, causing the system to enter an unrecoverable state that necessitates a complete device restart to restore normal operation. This behavior aligns with CWE-129, which addresses improper validation of input boundaries, and CWE-248, which covers exposure of an exception to the calling program.
From an operational perspective, this vulnerability creates a significant risk for network availability as it allows an adjacent attacker to remotely trigger device reloads without requiring authentication credentials. The adjacency requirement means that an attacker must be physically present on the same network segment as the target device, which reduces the attack surface but does not eliminate the threat entirely since network segmentation is not always perfect in enterprise environments. The DoS condition resulting from this vulnerability can have cascading effects throughout an organization's network infrastructure, potentially disrupting critical business operations and requiring network administrators to perform emergency maintenance procedures. Organizations may experience service degradation or complete network outages depending on the criticality of the affected devices and the timing of the attack.
The security implications extend beyond immediate service disruption as this vulnerability demonstrates the importance of robust input validation in network infrastructure software. Network administrators should implement monitoring solutions to detect unusual DHCPv6 traffic patterns and establish incident response procedures for rapid device recovery. Mitigation strategies include applying the latest security patches provided by Cisco, implementing network segmentation to limit adjacent access, and configuring access control lists to restrict DHCPv6 traffic where possible. This vulnerability aligns with ATT&CK technique T1499.004, which covers network disruption through resource exhaustion or device failure, and highlights the need for comprehensive security testing of network protocol implementations. Organizations should also consider implementing redundant network paths and backup systems to minimize the impact of such attacks, as the automatic device reload required for recovery can take several minutes to complete and may not be immediately apparent to network operators. The vulnerability underscores the necessity of continuous security updates and the importance of maintaining current threat intelligence to protect against known exploits in network infrastructure components.