CVE-2026-20104
MediumCVSS 6.1Summary
A vulnerability in the bootloader of Cisco IOS XE Software for Cisco Catalyst 9200, ESS9300, IE9310, IE9320, IE3500, and IE3505 switches could allow an authenticated local attacker with level-15 privileges or an unauthenticated attacker with physical access to execute arbitrary code at boot time and break the chain of trust. This is due to insufficient validation of software at boot time, enabling manipulation of loaded binaries to bypass integrity checks.
Risk Assessment
An attacker could bypass the requirement to run Cisco-signed images and execute unauthorized code early in the boot process, undermining a major security feature of the device. Cisco rated this vulnerability as High because it allows bypassing a key security mechanism.
Recommendation
Apply the Cisco IOS XE software updates referenced in the Cisco security advisory as soon as possible, and restrict physical access to devices and level-15 privileges to trusted administrators.
Other vulnerabilities in Cisco IOS XE Software
See all- CVE-2026-20272Critical
As part of an internal security review in Cisco IOS XE Software, multiple vulnerabilities related to improper neutralization of special elements (CWE-74) were discovered. Hardened software releases addressing these issues have been issued.
- CVE-2026-20267Critical
Vulnerability in Cisco IOS XE Software, discovered during an internal security review, involves improper access control issues classified under CWE-284. Hardened releases have been issued as a result.
- CVE-2023-20273HighActively exploited
A vulnerability in the web UI feature of Cisco IOS XE Software could allow an authenticated, remote attacker to inject commands with the privileges of root. This is due to insufficient input validation.
- CVE-2023-20198CriticalActively exploited
Cisco is providing an update for the ongoing investigation into observed exploitation of the web UI feature in Cisco IOS XE Software. The attacker exploited CVE-2023-20198 to gain initial access and issued a privilege 15 command to create a local user, then exploited another component (CVE-2023-20273) to elevate privilege to root and write an implant. CVE-2023-20198 has a CVSS score of 10.0, CVE-2023-20273 has a CVSS score of 7.2.
- CVE-2017-12319MediumActively exploited
A vulnerability in the Border Gateway Protocol (BGP) over an Ethernet Virtual Private Network (EVPN) for Cisco IOS XE Software could allow an unauthenticated, remote attacker to cause the device to reload, resulting in a denial of service (DoS) condition, or potentially corrupt the BGP routing table, which could result in network instability. The vulnerability exists due to changes in the implementation of the BGP MPLS-Based Ethernet VPN RFC (RFC 7432) draft between IOS XE software releases. When the BGP Inclusive Multicast Ethernet Tag Route or BGP EVPN MAC/IP Advertisement Route update packet is received, it could be possible that the IP address length field is miscalculated. This vulnerability affects all releases of Cisco IOS XE Software prior to software release 16.3 that support BGP EVPN configurations.
- CVE-2017-12229Critical
A vulnerability in the web-based user interface (web UI) of Cisco IOS XE 3.1 through 16.5 allows an unauthenticated remote attacker to bypass authentication to the REST API. The issue is due to insufficient input validation for the REST API.
- CVE-2026-20311Medium
A vulnerability in the web-based management interface of Cisco IOS XE Software could allow an authenticated, remote attacker with low privileges to cause a denial of service (DoS) condition on an affected device. This is due to insufficient error handling in the web-based management interface. An attacker could exploit this by authenticating with a malformed certificate, potentially causing the device to reload.
- CVE-2026-20308Medium
A vulnerability in the web-based management interface of Cisco IOS XE Software allows an authenticated remote attacker with low privileges to perform a DoS attack. The issue is due to insufficient input validation, and exploitation can make the interface unresponsive.
- CVE-2026-20273High
A vulnerability in Cisco IOS XE Software related to improper input validation (CWE-20), discovered during an internal security review. It is addressed in a software hardening release.
- CVE-2026-20271High
A vulnerability in Cisco IOS XE Software related to insufficient control flow management (CWE-691), discovered during an internal security review. It is addressed in software hardening releases.
Original NVD description (English source)
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.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS