CVE-2026-20104: A vulnerability in the bootloader of Cisco IOS XE Software for Cisco Catalyst 9200 Series Switches, Cisco Cata

Routine

MEDIUM 6.1MITIGATE

CVE-2026-20104 is a medium-severity flaw (CVSS 6.1) affecting ios xe. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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

Why this priority

No elevated risk signals yet

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	6.1 (Medium)
Attack vector	Physical
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.2% (top 95%)
CISA exploited list	No
Weakness	CWE-124
Published	2026-03-25
Last modified	2026-09-28

Publisher (CNA): Cisco Systems, Inc. · Vendor: cisco

Last updated 2026-09-28 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-03-25 16:16 UTCPublished CVE record published
2026-09-28 15:18 UTCUpdated Record last modified

cisco ios xe MITIGATE

Affected: 16.12.6 · 16.12.6a · 16.12.7 · 16.12.8 · 17.3.3 · 17.3.4 · 17.3.4b · 17.3.5

Fixed in: no fixed release known

Safe to downgrade to: a release before 16.12.6

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-20104?

ios xe: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2026-20104 being exploited?

CVE-2026-20104 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-20104 affect?

CVE-2026-20104 affects ios xe. Severity is medium (CVSS 6.1). 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

How urgent is CVE-2026-20104?

Priority 23/100. No elevated risk signals yet.

Software pages

iOS vulnerabilities · Cisco IOS XE vulnerabilities · Cisco vulnerabilities

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References

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