Medium Denial of service

CVE-2026-20173 — Cisco NX-OS Software Denial of Service Vulnerability

A vulnerability in Cisco NX-OS Software could allow an unauthenticated, remote attacker to exhaust system resources, causing a denial of service (DoS) condition. This vulnerability exists because rate limiting was improperly applied to some protocols. An attacker could exploit this vulnerability by sending a high rate of UDP or TCP connections to a data plane interface on an affected device. A successful exploit could allow the attacker to cause instability to various routing and control plane protocols through some packet loss and temporary disruptions, causing a DoS condition. This DoS condition will clear without manual intervention soon after the high rate of traffic is stopped.

Published Oct 7, 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 0.4% (30-day exploitation probability)+4
Technical severity (medium)+3
Automatable exploitation (SSVC)+3

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

0.37%

ahead of 30% of scored CVEs · Oct 14, 2026

Affects

Cisco

Cisco NX-OS Software

CVSS base

5.8

Medium · 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

Yes

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).
The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
No fix documented in the sources: reduce exposure and monitor the vendor advisory.
Search available logs for exploit probes matching the vulnerability class (denial of service), 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 8.2(5)version 7.3(5)D1(1)version 8.4(2)version 8.4(3)version 9.2(3)version 9.2(2v)version 7.3(4)D1(1)version 8.2(1) and 103 more version 9.2(1)version 9.2(2t)version 9.2(3y)version 9.3(2)version 8.1(1)version 8.2(2)version 8.3(2)version 7.3(2)D1(3a)version 9.2(4)version 8.1(2)version 7.3(3)D1(1)version 8.2(3)version 8.4(1)version 7.3(0)DX(1)version 7.3(2)D1(1)version 9.3(1)version 7.3(2)D1(2)version 8.2(4)version 9.3(1z)version 9.2(2)version 8.1(2a)version 7.3(2)D1(3)version 8.3(1)version 7.3(1)D1(1)version 7.3(0)D1(1)version 9.3(3)version 7.3(2)D1(1d)version 9.3(4)version 7.3(6)D1(1)version 8.2(6)version 9.3(5)version 9.3(6)version 8.4(4)version 7.3(7)D1(1)version 9.3(5w)version 8.2(7)version 9.3(7)version 9.3(7k)version 7.3(8)D1(1)version 9.3(7a)version 8.2(7a)version 9.3(8)version 8.4(4a)version 8.4(5)version 8.2(8)version 9.3(9)version 7.3(9)D1(1)version 8.4(6)version 9.3(10)version 8.2(9)version 10.3(1)version 8.4(7)version 10.3(2)version 8.4(6a)version 9.3(11)version 10.3(3)version 8.2(10)version 9.3(12)version 10.4(1)version 8.4(8)version 10.3(99w)version 10.3(3w)version 10.3(99x)version 10.3(3o)version 8.4(9)version 10.3(4)version 10.3(3p)version 10.3(4a)version 10.4(2)version 10.3(3q)version 9.3(13)version 8.2(11)version 10.3(5)version 10.4(3)version 10.3(3x)version 10.3(4g)version 10.5(1)version 8.4(10)version 10.3(3r)version 10.3(6)version 9.3(14)version 10.4(4)version 10.3(4h)version 10.5(2)version 8.4(11)version 10.3(7)version 10.4(5)version 10.5(3)version 9.3(15)version 10.4(4g)version 10.5(4)version 8.4(12)version 10.5(3t)version 10.3(8)version 10.4(6)version 10.5(3s)version 10.5(3e)version 10.5(3o)version 9.3(16)version 10.5(3p)version 10.4(7)version 10.5(5)version 9.3(17)	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

Network

Attack complexity

Low

Privileges required

None

User interaction

None

Scope

Changed

Confidentiality

None

Integrity

None

Availability

Low

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
5.8	CVSS 3.1	Medium	3.9	1.4	psirt@cisco.com via NIST National Vulnerability Database
5.8	CVSS 3.1	Medium	—	—	cisco via CVE Program (cve.org) e CISA ADP

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

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-770 · Allocation of Resources Without Limits or Throttling

Other CVEs with this weakness →

EPSS over time FIRST

Oct 13, 2026 → Oct 14, 2026 · 2 reading(s) · max 0.37%

Detection

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

Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
Track CPU/memory spikes and availability drops correlated with request patterns.

web/proxy/WAF logsnetwork IDS/IPSresource metrics

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 · 5.8
Oct 13, 2026 · NIST National Vulnerability Database
Source status changed · → Awaiting Analysis
Oct 13, 2026 · NIST National Vulnerability Database
Record created in this database
Oct 13, 2026 · NIST National Vulnerability Database
CVE published
Oct 7, 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-nscpdos-S
NIST National Vulnerability Database

Elsewhere on this site

Cisco
every CVE for this vendor

Denial of service
same class

CWE-770
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
High CVE-2026-76458 Cisco NX-OS Software Security Hardening Release: October 2026 - Improper Handling of Exceptional Conditions 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-2026-20173 is "Cisco NX-OS Software Denial of Service Vulnerability", rated Medium. 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 5.8 describes technical severity. EPSS 0.37% 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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