If left unpatched, CVE-2026-20104 could lead to major system disruptions or data loss.
Status: Awaiting Analysis
Last updated: 🕒 26 Mar 2026, 15:13 UTC
Originally published on: 🕓 25 Mar 2026, 16:16 UTC
CVSS Release: version 3
psirt@cisco.com
Primary
CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
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.
The exploitability of CVE-2026-20104 depends on two key factors: attack complexity (the level of effort required to execute an exploit) and privileges required (the access level an attacker needs).
With low attack complexity and no required privileges, CVE-2026-20104 is an easy target for cybercriminals. Organizations should prioritize immediate mitigation measures to prevent unauthorized access and data breaches.
A lower complexity and fewer privilege requirements make exploitation easier. Security teams should evaluate these aspects to determine the urgency of mitigation strategies, such as patch management and access control policies.
Attack Complexity (AC) measures the difficulty in executing an exploit. A high AC means that specific conditions must be met, making an attack more challenging, while a low AC means the vulnerability can be exploited with minimal effort.
Privileges Required (PR) determine the level of system access necessary for an attack. Vulnerabilities requiring no privileges are more accessible to attackers, whereas high privilege requirements limit exploitation to authorized users with elevated access.
Above is the CVSS Sub-score Breakdown for CVE-2026-20104, illustrating how Base, Impact, and Exploitability factors combine to form the overall severity rating. A higher sub-score typically indicates a more severe or easier-to-exploit vulnerability.
Below is the Impact Analysis for CVE-2026-20104, showing how Confidentiality, Integrity, and Availability might be affected if the vulnerability is exploited. Higher values usually signal greater potential damage.
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