CVE-2026-20104: A vulnerability in the bootloader of Cisco IOS XE Software for Cisco Catalyst 9200 Series Switches, Cisco Catalyst ESS9300 Embedded Series Switches, C...

Description

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.

Metrics

CVSS 3.1

6.1/10

CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

EPSS Probability

0.16%

5.8th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-124

Affected Software

Source: CNA advisory (CVE.org). NVD analysis pending.

Vendor	Product	Versions
Cisco	Cisco IOS XE Software	16.12.8; 16.12.6; 16.12.6a; 16.12.7; 17.3.3; 17.3.4; 17.3.5; 17.3.6; 17.3.4b; 17.3.7; 17.3.8; 17.3.8a; 17.4.1; 17.5.1; 17.6.1; 17.6.2; 17.6.3; 17.6.1y; 17.6.4; 17.6.5; 17.6.6; 17.6.6a; 17.6.5a; 17.6.7; 17.6.8; 17.7.1; 17.7.1a; 17.10.1; 17.8.1; 17.8.1a; 17.9.1; 17.9.2; 17.9.1a; 17.9.3; 17.9.4; 17.9.5; 17.9.4a; 17.9.5b; 17.9.6; 17.9.6a; 17.9.7; 17.9.8; 17.11.1; 17.12.1; 17.12.2; 17.12.3; 17.12.4; 17.12.5; 17.12.6; 17.13.1; 17.14.1; 17.15.1; 17.15.2; 17.15.3; 17.15.4; 17.16.1; 17.17.1; 17.18.1; 17.18.2

References

https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-xe-secureboot-bypass-B6uYxYSZ

Timeline

Published: Mar 25, 2026
Last Modified: Jun 17, 2026
Status: Awaiting Analysis

Frequently Asked Questions

What is CVE-2026-20104?

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.

How severe is CVE-2026-20104?

CVE-2026-20104 has a CVSS score of 6.1/10 (MEDIUM severity). The EPSS model estimates a 0.16% probability of exploitation in the next 30 days.

How do I fix CVE-2026-20104?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

How Strix Helps

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