Critical Cisco IOS XR Vulnerability Allows Attackers to Execute Commands as Root

Cisco has released security updates to address two high‑severity vulnerabilities in its IOS XR Software that could allow attackers to execute commands as the root user or gain full administrative control over affected devices.

Because IOS XR powers many enterprise and service provider routers, successful exploitation could severely impact network infrastructure and operational security.

High-Severity IOS XR Privilege Escalation Flaws

The vulnerabilities are tracked as CVE-2026-20040 and CVE-2026-20046. Both issues have been assigned a CVSS base score of 8.8, indicating a high severity risk.

If exploited, attackers could escalate privileges and perform unauthorized actions on network devices that are often deployed as critical backbone infrastructure.

Importantly, Cisco notes that these vulnerabilities can be exploited independently. Attackers do not need to chain the flaws together to achieve privilege escalation, which increases the risk for organizations running vulnerable versions of IOS XR.

The first vulnerability, CVE-2026-20040, is a privilege escalation flaw in the Command-Line Interface (CLI). The issue occurs because IOS XR fails to properly validate user-supplied arguments passed to certain CLI commands.

An authenticated attacker with low-level access to the device could exploit the flaw by entering specially crafted commands in the CLI interface.

If successful, the attacker could elevate their privileges and execute arbitrary commands as the root user on the underlying operating system.

Root-level access effectively provides complete control over the device, allowing attackers to modify system configurations, install malicious code, or disrupt network operations.

The second vulnerability, CVE-2026-20046, affects Cisco IOS XRv 9000 routers specifically. This flaw stems from the incorrect mapping of a CLI command to task groups within the system source code.

Cisco IOS XR uses task groups to enforce role-based access controls and restrict what commands different users can execute.

Due to the improper mapping, a low-privileged attacker could run a specific CLI command that bypasses these authorization checks.

By exploiting this flaw, the attacker could escalate privileges and perform administrative actions that should normally be restricted to high-privilege accounts.

Cisco confirmed that other operating systems, including IOS Software, IOS XE Software, and NX-OS Software, are not affected by these vulnerabilities.

Cisco strongly advises organizations to update affected systems immediately to patched software releases. The remediation process varies slightly between the two vulnerabilities.

For CVE-2026-20040, no workaround exists. Administrators must apply the available software updates or install Software Maintenance Updates (SMUs) to mitigate the issue.

For CVE-2026-20046, organizations using TACACS+ authentication, authorization, and accounting (AAA) command authorization can implement a temporary workaround.

This configuration allows administrators to restrict command execution and prevent non-privileged users from accessing sensitive CLI commands.

Cisco has released fixes in updated IOS XR versions, including 25.2.21 and 25.4.2. Administrators running older versions, such as 25.1 or earlier, as well as those using the 25.3 release branch, are urged to upgrade or apply SMUs as soon as possible to reduce exposure to potential attacks.

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