CVE-2026-20104

CVE-2026-20104 is a medium-severity vulnerability in Cisco Ios Xe with a CVSS 3.x base score of 6.1. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-124.

Key facts

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.

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 3.x base score of 6.1, rated medium severity. It is exploitable over physical access with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability none.
Is CVE-2026-20104 being actively exploited?
It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (5th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-20104?
CVE-2026-20104 primarily affects Cisco Ios Xe. In total, 59 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2026-20104?
Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-20104 have an EU (EUVD) identifier?
Yes. CVE-2026-20104 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-15435.
When was CVE-2026-20104 published?
CVE-2026-20104 was published on 2026-03-25 and last updated on 2026-09-28.

References

Affected products (59)

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