VulnerabilityPublished 25 Feb 2026

CVE-2026-20051: Cisco NX-OS Software · Use of Uninitialized Variable

Affects Cisco NX-OS SoftwareSource CVE Database V5

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Not known to be exploited · CVSS 7.4 High.

Data as of 30 Oct 2026, 06:59 UTC

CVSS 3.1 base score

7.4High

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.1% chance of exploitation in 30 days – higher than 6% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H

Attack Vector: Adjacent
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Changed
Confidentiality: None
Integrity: None
Availability: High

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Adjacent: The vulnerable component is bound to the network stack, but the attack is limited at the protocol level to a logically adjacent topology. This can mean an attack must be launched from the same shared physical (e.g., Bluetooth or IEEE 802.11) or logical (e.g., local IP subnet) network, or from within a secure or otherwise limited administrative domain (e.g., MPLS, secure VPN to an administrative network zone).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Changed: An exploited vulnerability can affect resources beyond the security scope managed by the security authority of the vulnerable component. In this case, the vulnerable component and the impacted component are different and managed by different security authorities.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 25 Feb 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 29 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Affected software

Product	Affected	Fixed in
CiscoCisco NX-OS Software	Affected 9.2(1) – 10.6(1s) 75 affected builds	Fixed in–

AI-suggested

To mitigate CVE-2026-20051, organizations should first identify all Cisco Nexus 3600 and 9500-R series switches running affected NX-OS versions. Immediate steps include: 1) Applying Cisco-released patches or software updates that address this vulnerability as soon as they become available; 2) Implementing strict network segmentation and access controls to limit Layer 2 adjacency to trusted devices only, reducing the attack surface; 3) Monitoring network traffic for signs of abnormal Layer 2 loops or unusual VxLAN traffic patterns using advanced network monitoring and anomaly detection tools; 4) Preparing incident response procedures to quickly flap affected interfaces and stop malicious traffic if a loop is detected; 5) Engaging Cisco Technical Assistance Center (TAC) for guidance and support in case of suspected exploitation; 6) Reviewing and hardening EVPN and VxLAN configurations to ensure they follow best practices and minimize exposure; 7) Employing network access control (NAC) solutions to prevent unauthorized devices from connecting at Layer 2; 8) Conducting regular network audits to identify and remediate misconfigurations that could facilitate exploitation. These targeted measures go beyond generic advice by focusing on limiting adjacency, proactive detection, and rapid response to traffic loops.

Description

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. 

Impact

The primary impact of CVE-2026-20051 is a denial of service condition on critical network infrastructure devices, specifically Cisco Nexus 3600 and 9500-R series switches. By triggering a Layer 2 VxLAN traffic loop, an attacker can cause oversubscription of bandwidth on network interfaces, resulting in dropped data plane traffic and network outages. This can severely disrupt enterprise and data center network operations, impacting availability of services dependent on these switches. The vulnerability affects a broad range of NX-OS versions, increasing the scope of potentially impacted devices globally. Organizations relying on these Cisco platforms for core switching and EVPN services face risks of network instability, degraded performance, and potential downtime. Since exploitation requires Layer 2 adjacency, attackers with access to the local network segment or compromised devices within the same broadcast domain pose a significant threat. The lack of authentication requirement lowers the barrier for exploitation once adjacency is achieved. Although no known exploits are reported, the potential for widespread network disruption makes this vulnerability a critical concern for network administrators and security teams.

References

sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-nxos-ether-dos-Kv8YNWZ4 (opens in a new tab)

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 26 Feb 2026, 00:02 UTC

Technical details

References

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