High Memory corruption

CVE-2026-20051 — 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. 

Published Feb 25, 2026 · Updated Oct 13, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP · CNA: cisco

Low

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.

How the score was calculated

EPSS 0.2% (30-day exploitation probability)+1
Technical severity (high)+6

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation

Not confirmed

Not in CISA KEV — an absence of record, not proof it is unexploited.

EPSS FIRST

0.16%

ahead of 4% of scored CVEs · Oct 14, 2026

Affects

Cisco

Cisco NX-OS Software

CVSS base

7.4

High · 2 source(s)

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Exploitation

None

none · proof-of-concept · active

Automatable

can an attacker script the kill-chain steps

Technical impact

Partial

partial · total control of the vulnerable component

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

Identify exposed assets running the affected vendor/product/version combinations (Cisco Cisco NX-OS Software).
No fix documented in the sources: reduce exposure and monitor the vendor advisory.
Search available logs for exploit probes matching the vulnerability class (memory corruption), errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

Vendor	Product	Versions	Status	Source
Cisco	Cisco NX-OS Software	version 10.2(7)version 10.4(4)version 9.3(14)version 10.3(6)version 10.3(3r)version 10.2(8)version 10.5(1)version 10.3(4g) and 67 more version 10.3(3x)version 10.4(3)version 10.3(4h)version 10.3(5)version 9.3(13)version 10.3(3q)version 10.4(2)version 10.3(4a)version 10.3(3p)version 10.3(4)version 10.3(3o)version 10.6(1)version 10.5(3p)version 10.6(1s)version 9.3(16)version 10.5(3o)version 10.5(3e)version 10.5(3s)version 10.4(6)version 10.3(8)version 10.5(3t)version 10.3(3w)version 10.5(4)version 10.4(4g)version 9.3(15)version 10.2(9)version 10.5(3)version 10.4(5)version 10.3(7)version 10.5(2)version 9.2(2)version 9.3(7a)version 10.2(1)version 9.3(7k)version 9.3(7)version 9.3(5w)version 9.3(6)version 9.3(5)version 9.3(4)version 9.3(3)version 9.3(8)version 9.3(1z)version 9.3(1)version 9.2(4)version 9.3(2)version 9.2(3y)version 9.2(2t)version 9.2(1)version 9.2(2v)version 10.2(4)version 10.2(6)version 10.4(1)version 10.2(3v)version 9.3(12)version 10.2(5)version 10.3(3)version 9.3(11)version 10.3(2)version 9.2(3)version 10.3(1)version 10.2(2a)version 9.3(10)version 10.2(3t)version 10.2(3)version 9.3(9)version 10.2(2)version 10.2(1q)	Vulnerable	CVE Program (cve.org) e CISA ADP

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector

Adjacent

Attack complexity

Low

Privileges required

None

User interaction

None

Scope

Changed

Confidentiality

None

Integrity

None

Availability

High

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

Score	Version	Severity	Expl.	Impact	Scored by
7.4	CVSS 3.1	High	2.8	4.0	psirt@cisco.com via NIST National Vulnerability Database
7.4	CVSS 3.1	High	—	—	cisco via CVE Program (cve.org) e CISA ADP

CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H (score shown at the top: psirt@cisco.com)

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-457 · Use of Uninitialized Variable

Other CVEs with this weakness →

EPSS over time FIRST

Oct 13, 2026 → Oct 14, 2026 · 2 reading(s) · max 0.16%

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

Correlate service crashes/restarts with inbound traffic; repeated crashes may indicate attempts.

endpoint telemetry (EDR)crash dumps

Timeline

What happened to this CVE, newest first.

2026
Affected products added · cisco/cisco nx-os software
Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
SSVC assessment updated
Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
Record published
Oct 13, 2026
CVSS changed · 7.4
Oct 13, 2026 · NIST National Vulnerability Database
Source status changed · → Deferred
Oct 13, 2026 · NIST National Vulnerability Database
Record created in this database
Oct 13, 2026 · NIST National Vulnerability Database
CVE published
Feb 25, 2026 · cisco

Source activity

Repeated readings are counted rather than listed.

1× Official description updated · Oct 13, 2026 – Oct 13, 2026

References

1 on the record

sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-nxos-ether-dos
NIST National Vulnerability Database

Elsewhere on this site

Cisco
every CVE for this vendor

Memory corruption
same class

CWE-457
other pages naming this weakness

Related CVEs (same products)

Critical CVE-2026-76501 Cisco Nexus 9000 Series Switches SRv6 OAM (NGOAM) Remote Code Execution Vulnerability 8d
Critical CVE-2026-76486 Cisco Nexus 3000 and 9000 Series Switches VXLAN OAM (NGOAM) Remote Code Execution Vulnerability 8d
Critical CVE-2026-76485 Cisco Nexus 3000 and 9000 Series Switches VXLAN OAM (NGOAM) Remote Code Execution Vulnerability 8d
Critical CVE-2026-76471 Cisco NX-OS Software NX-API Remote Code Execution Vulnerability 8d
Critical CVE-2026-76465 Cisco Nexus 3000 and 9000 Series Switches MPLS OAM Remote Code Execution Vulnerability 8d
Critical CVE-2026-76459 Cisco NX-OS Software Security Hardening Release: October 2026 - Out-of-bounds Write Vulnerabilities 8d

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

No fixed version, patch or mitigation documented.
No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2026-20051 is "Cisco Nexus 3600-R and 9500-R Series Switching Platforms Layer 2 Loop Denial of Service Vulnerability", rated High. It affects Cisco NX-OS Software (Cisco); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 7.4 describes technical severity. EPSS 0.16% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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