High Denial of service

CVE-2026-20084 — Uncontrolled Resource Consumption in Cisco Cisco IOS XE Software

A vulnerability in the DHCP snooping feature of Cisco IOS XE Software could allow an unauthenticated, remote attacker to cause BOOTP packets to be forwarded between VLANs, resulting in a denial of service (DoS) condition. This vulnerability is due to improper handling of BOOTP packets on Cisco Catalyst 9000 Series Switches. An attacker could exploit this vulnerability by sending BOOTP request packets to an affected device. A successful exploit could allow an attacker to forward BOOTP packets from one VLAN to another, resulting in BOOTP VLAN leakage and potentially leading to high CPU utilization. This makes the device unreachable (either through console or remote management) and unable to forward traffic, resulting in a DoS condition. Note: This vulnerability can be exploited with either unicast or broadcast BOOTP packets. There are workarounds that address this vulnerability.

Published Mar 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 0.4% (30-day exploitation probability)+4
Technical severity (high)+6
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

0.35%

ahead of 27% of scored CVEs · Oct 14, 2026

Affects

Cisco

Cisco IOS XE Software and 1 more

CVSS base

8.6

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

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 IOS XE Software, Cisco Ios Xe).
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 IOS XE Software	version 17.6.6aversion 17.9.4version 17.9.3version 17.9.2version 17.9.1version 17.8.1version 17.10.1bversion 17.10.1 and 99 more version 17.7.1version 17.6.8version 17.6.7version 17.6.5aversion 17.9.5version 17.6.6version 17.6.5version 17.6.4version 17.6.1yversion 17.6.3version 17.6.2version 17.6.1version 17.5.1version 17.4.1version 17.3.8aversion 17.3.8version 17.12.1z5version 17.18.1version 17.17.1version 17.16.1version 17.15.4dversion 17.15.4version 17.15.2bversion 17.15.3version 17.15.2version 17.15.1version 17.14.1version 17.13.1version 17.3.7version 17.12.5version 17.12.4version 17.12.3version 17.12.2version 17.12.1version 17.11.1version 17.9.8version 17.9.7version 17.9.6aversion 17.9.6version 17.9.4aversion 16.10.1version 16.12.8version 16.12.3version 16.12.2version 16.12.1cversion 16.12.1sversion 16.12.1version 16.11.1sversion 16.11.1bversion 16.11.1version 16.10.1eversion 16.10.1sversion 16.12.2sversion 16.9.8version 16.9.7version 16.9.6version 16.9.5version 16.9.4version 16.9.3version 16.9.1sversion 16.9.2version 16.9.1version 16.8.1sversion 16.8.1aversion 17.1.1sversion 17.3.6version 17.3.5version 17.3.4version 17.3.2aversion 17.3.3version 17.3.2version 17.3.1version 17.2.1aversion 17.2.1version 17.1.3version 17.1.1tversion 16.8.1version 17.1.1version 16.12.7version 16.12.6aversion 16.12.5bversion 16.12.6version 16.12.5version 16.12.4aversion 16.12.3aversion 16.12.3sversion 16.12.4version 16.6.1version 16.6.2version 16.6.3version 16.6.4version 16.6.5version 16.6.4aversion 16.6.6version 16.6.7version 16.6.8version 16.6.9version 16.6.10version 16.7.1	Vulnerable	CVE Program (cve.org) e CISA ADP
Cisco	Ios Xe	version 16.6.1version 16.6.2version 16.6.3version 16.6.4version 16.6.4aversion 16.6.5version 16.6.6version 16.6.7 and 99 more version 16.6.8version 16.6.9version 16.6.10version 16.7.1version 16.8.1version 16.8.1aversion 16.8.1sversion 16.9.1version 16.9.1sversion 16.9.2version 16.9.3version 16.9.4version 16.9.5version 16.9.6version 16.9.7version 16.9.8version 16.10.1version 16.10.1eversion 16.10.1sversion 16.11.1version 16.11.1bversion 16.11.1sversion 16.12.1version 16.12.1cversion 16.12.1sversion 16.12.2version 16.12.2sversion 16.12.3version 16.12.3aversion 16.12.3sversion 16.12.4version 16.12.4aversion 16.12.5version 16.12.5bversion 16.12.6version 16.12.6aversion 16.12.7version 16.12.8version 17.1.1version 17.1.1sversion 17.1.1tversion 17.1.3version 17.2.1version 17.2.1aversion 17.3.1version 17.3.2version 17.3.2aversion 17.3.3version 17.3.4version 17.3.5version 17.3.6version 17.3.7version 17.3.8version 17.3.8aversion 17.4.1version 17.5.1version 17.6.1version 17.6.1yversion 17.6.2version 17.6.3version 17.6.4version 17.6.5version 17.6.5aversion 17.6.6version 17.6.6aversion 17.6.7version 17.6.8version 17.7.1version 17.8.1version 17.9.1version 17.9.2version 17.9.3version 17.9.4version 17.9.4aversion 17.9.5version 17.9.6version 17.9.6aversion 17.9.7version 17.9.8version 17.10.1version 17.10.1bversion 17.11.1version 17.12.1version 17.12.1z5version 17.12.2version 17.12.3version 17.12.4version 17.12.5version 17.13.1version 17.14.1version 17.15.1version 17.15.2version 17.15.2bversion 17.15.3version 17.15.4version 17.15.4dversion 17.16.1version 17.17.1version 17.18.1	Vulnerable	NIST National Vulnerability Database

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

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
8.6	CVSS 3.1	High	3.9	4.0	psirt@cisco.com via NIST National Vulnerability Database
8.6	CVSS 3.1	High	—	—	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:H (score shown at the top: psirt@cisco.com)

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-400 · Uncontrolled Resource Consumption

Other CVEs with this weakness →

EPSS over time FIRST

Oct 13, 2026 → Oct 14, 2026 · 2 reading(s) · max 0.35%

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 ios xe 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 · 8.6
Oct 13, 2026 · NIST National Vulnerability Database
Source status changed · → Analyzed
Oct 13, 2026 · NIST National Vulnerability Database
Record created in this database
Oct 13, 2026 · NIST National Vulnerability Database
CVE published
Mar 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-bootp-WuBhNBxA
Vendor Advisory, NIST National Vulnerability Database

Elsewhere on this site

Cisco
every CVE for this vendor

Denial of service
same class

CWE-400
other pages naming this weakness

Related CVEs (same products)

Medium CVE-2026-20308 Cisco IOS XE Software Web-Based Management Interface Vulnerability Aug 5, 2026
Medium CVE-2026-20311 Cisco IOS XE Software Web UI Denial of Service Vulnerability Aug 5, 2026
High CVE-2026-20301 Cisco IOS Software and IOS XE Software Extensible Messaging Client Protocol Denial of Service Vulnerability Aug 5, 2026
Critical CVE-2026-20272 Cisco IOS XE Software Security Hardening Release Aug 5, 2026
High CVE-2026-20273 Cisco IOS XE Software Security Hardening Release Aug 5, 2026
High CVE-2026-20269 Cisco IOS XE Software Security Hardening Release Aug 5, 2026

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-2026-20084 is "Uncontrolled Resource Consumption in Cisco Cisco IOS XE Software", rated High. It affects Cisco IOS XE Software (Cisco); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 8.6 describes technical severity. EPSS 0.35% 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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