Medium

CVE-2026-20104 — A vulnerability in the bootloader of Cisco IOS XE Software for Cisco Catalyst 9200…

A vulnerability in the bootloader of Cisco IOS XE Software for Cisco Catalyst 9200 Series Switches, Cisco Catalyst ESS9300 Embedded Series Switches, Cisco Catalyst IE9310 and IE9320 Rugged Series Switches, and Cisco IE3500 and IE3505 Rugged Series Switches could allow an authenticated, local attacker with level-15 privileges or an unauthenticated attacker with physical access to an affected device to execute arbitrary code at boot time and break the chain of trust. This vulnerability is due to insufficient validation of software at boot time. An attacker could exploit this vulnerability by manipulating the loaded binaries on an affected device to bypass some of the integrity checks that are performed during the boot process. A successful exploit could allow the attacker to execute code that bypasses the requirement to run Cisco-signed images. Cisco has assigned this security advisory a Security Impact Rating (SIR) of High rather than Medium as the score indicates because this vulnerability allows an attacker to bypass a major security feature of a device.

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 0.2% (30-day exploitation probability)+1
Technical severity (medium)+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

0.15%

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

Affects

Cisco

Cisco IOS XE Software and 1 more

CVSS base

6.1

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

can an attacker script the kill-chain steps

Technical impact

Total

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).
No fix documented in the sources: reduce exposure and monitor the vendor advisory.
Search available logs for exploit probes, 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 16.12.8version 16.12.6version 16.12.6aversion 16.12.7version 17.3.3version 17.3.4version 17.3.5version 17.3.6 and 51 more version 17.3.4bversion 17.3.7version 17.3.8version 17.3.8aversion 17.4.1version 17.5.1version 17.6.1version 17.6.2version 17.6.3version 17.6.1yversion 17.6.4version 17.6.5version 17.6.6version 17.6.6aversion 17.6.5aversion 17.6.7version 17.6.8version 17.7.1version 17.7.1aversion 17.10.1version 17.8.1version 17.8.1aversion 17.9.1version 17.9.2version 17.9.1aversion 17.9.3version 17.9.4version 17.9.5version 17.9.4aversion 17.9.5bversion 17.9.6version 17.9.6aversion 17.9.7version 17.9.8version 17.11.1version 17.12.1version 17.12.2version 17.12.3version 17.12.4version 17.12.5version 17.12.6version 17.13.1version 17.14.1version 17.15.1version 17.15.2version 17.15.3version 17.15.4version 17.16.1version 17.17.1version 17.18.1version 17.18.2	Vulnerable	CVE Program (cve.org) e CISA ADP
Cisco	Ios Xe	version 16.12.6version 16.12.6aversion 16.12.7version 16.12.8version 17.3.3version 17.3.4version 17.3.4bversion 17.3.5 and 51 more version 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 17.7.1aversion 17.8.1version 17.8.1aversion 17.9.1version 17.9.1aversion 17.9.2version 17.9.3version 17.9.4version 17.9.4aversion 17.9.5version 17.9.5bversion 17.9.6version 17.9.6aversion 17.9.7version 17.9.8version 17.10.1version 17.11.1version 17.12.1version 17.12.2version 17.12.3version 17.12.4version 17.12.5version 17.12.6version 17.13.1version 17.14.1version 17.15.1version 17.15.2version 17.15.3version 17.15.4version 17.16.1version 17.17.1version 17.18.1version 17.18.2	Vulnerable	NIST National Vulnerability Database

Attack characteristics

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

Attack vector

Physical

Attack complexity

Low

Privileges required

None

User interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

None

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
6.1	CVSS 3.1	Medium	0.9	5.2	psirt@cisco.com via NIST National Vulnerability Database
6.1	CVSS 3.1	Medium	—	—	cisco via CVE Program (cve.org) e CISA ADP

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

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-124

Other CVEs with this weakness →

EPSS over time FIRST

Oct 13, 2026 → Oct 14, 2026 · 2 reading(s) · max 0.15%

Detection

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

Local/physical vector: focus on endpoint telemetry (EDR) from affected hosts.

endpoint telemetry (EDR)

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 · 6.1
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-xe-secureboot-
Vendor Advisory, NIST National Vulnerability Database

Elsewhere on this site

Cisco
every CVE for this vendor

CWE-124
other pages naming this weakness

Related CVEs (same products)

Medium CVE-2026-20115 Cleartext Transmission of Sensitive Information in Cisco Cisco IOS XE Software Mar 25, 2026
Medium CVE-2026-20114 A vulnerability in the Lobby Ambassador web-based management API of Cisco IOS XE… Mar 25, 2026
High CVE-2026-20125 A vulnerability in the HTTP Server feature of Cisco IOS Software and Cisco IOS XE… Mar 25, 2026
Medium CVE-2026-20113 A vulnerability in the web-based Cisco IOx application hosting environment management… Mar 25, 2026
Medium CVE-2026-20112 Cross-site Scripting (XSS) in Cisco Cisco IOS XE Software Mar 25, 2026
Medium CVE-2026-20110 A vulnerability in the CLI of Cisco IOS XE Software could allow an authenticated, local… Mar 25, 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-2026-20104 is "A vulnerability in the bootloader of Cisco IOS XE Software for Cisco Catalyst 9200…", rated Medium. 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 6.1 describes technical severity. EPSS 0.15% 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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