CVE-2026-20051 is a vulnerability in Cisco Nx Os
Published on February 25, 2026
Cisco Nexus 3600-R and 9500-R Series Switching Platforms Layer 2 Loop Denial of Service Vulnerability
A vulnerability with the Ethernet VPN (EVPN) Layer 2 ingress packet processing of Cisco Nexus 3600 Platform Switches and Cisco Nexus 9500-R Series Switching Platforms could allow an unauthenticated, adjacent attacker to trigger a Layer 2 traffic loop.
This vulnerability is due to a logic error when processing a crafted Layer 2 ingress frame. An attacker could exploit this vulnerability by sending a stream of crafted Ethernet frames through the targeted device. A successful exploit could allow the attacker to cause a Layer 2 Virtual eXtensible LAN (VxLAN) traffic loop, which, in turn, could result in a denial of service (DoS) condition. This Layer 2 loop could oversubscribe the bandwidth on network interfaces, which would result in all data plane traffic being dropped. To exploit this vulnerability, the attacker must be Layer 2-adjacent to the affected device.
Note: To stop active exploitation of this vulnerability, manual intervention is required to both stop the crafted traffic and flap all involved network interfaces. For additional assistance if a Layer 2 loop that is related to this vulnerability is suspected, contact the Cisco Technical Assistance Center (TAC) or the proper support provider.
Vulnerability Analysis
Weakness Type
Use of Uninitialized Variable
The code uses a variable that has not been initialized, leading to unpredictable or unintended results. In some languages such as C and C++, stack variables are not initialized by default. They generally contain junk data with the contents of stack memory before the function was invoked. An attacker can sometimes control or read these contents. In other languages or conditions, a variable that is not explicitly initialized can be given a default value that has security implications, depending on the logic of the program. The presence of an uninitialized variable can sometimes indicate a typographic error in the code.
Products Associated with CVE-2026-20051
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Affected Versions
Cisco NX-OS Software:- Version 9.2(3) is affected.
- Version 9.2(2v) is affected.
- Version 9.2(1) is affected.
- Version 9.2(2t) is affected.
- Version 9.2(3y) is affected.
- Version 9.3(2) is affected.
- Version 9.2(4) is affected.
- Version 9.3(1) is affected.
- Version 9.3(1z) is affected.
- Version 9.2(2) is affected.
- Version 9.3(3) is affected.
- Version 9.3(4) is affected.
- Version 9.3(5) is affected.
- Version 9.3(6) is affected.
- Version 9.3(5w) is affected.
- Version 9.3(7) is affected.
- Version 9.3(7k) is affected.
- Version 10.2(1) is affected.
- Version 9.3(7a) is affected.
- Version 9.3(8) is affected.
- Version 10.2(1q) is affected.
- Version 10.2(2) is affected.
- Version 9.3(9) is affected.
- Version 10.2(3) is affected.
- Version 10.2(3t) is affected.
- Version 9.3(10) is affected.
- Version 10.2(2a) is affected.
- Version 10.3(1) is affected.
- Version 10.2(4) is affected.
- Version 10.3(2) is affected.
- Version 9.3(11) is affected.
- Version 10.3(3) is affected.
- Version 10.2(5) is affected.
- Version 9.3(12) is affected.
- Version 10.2(3v) is affected.
- Version 10.4(1) is affected.
- Version 10.2(6) is affected.
- Version 10.3(3w) is affected.
- Version 10.3(3o) is affected.
- Version 10.3(4) is affected.
- Version 10.3(3p) is affected.
- Version 10.3(4a) is affected.
- Version 10.4(2) is affected.
- Version 10.3(3q) is affected.
- Version 9.3(13) is affected.
- Version 10.3(5) is affected.
- Version 10.2(7) is affected.
- Version 10.4(3) is affected.
- Version 10.3(3x) is affected.
- Version 10.3(4g) is affected.
- Version 10.5(1) is affected.
- Version 10.2(8) is affected.
- Version 10.3(3r) is affected.
- Version 10.3(6) is affected.
- Version 9.3(14) is affected.
- Version 10.4(4) is affected.
- Version 10.3(4h) is affected.
- Version 10.5(2) is affected.
- Version 10.3(7) is affected.
- Version 10.4(5) is affected.
- Version 10.5(3) is affected.
- Version 10.2(9) is affected.
- Version 9.3(15) is affected.
- Version 10.4(4g) is affected.
- Version 10.5(4) is affected.
- Version 10.6(1) is affected.
- Version 10.5(3t) is affected.
- Version 10.3(8) is affected.
- Version 10.4(6) is affected.
- Version 10.5(3s) is affected.
- Version 10.5(3e) is affected.
- Version 10.5(3o) is affected.
- Version 9.3(16) is affected.
- Version 10.6(1s) is affected.
- Version 10.5(3p) is affected.
Exploit Probability
EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.