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CVE-2026-20040 Cisco CVE debrief

CVE-2026-20040 is a high-severity vulnerability in the Command-Line Interface (CLI) of Cisco IOS XR Software. An authenticated, local attacker could exploit this vulnerability to execute arbitrary commands as root on the underlying operating system of an affected device. The vulnerability is due to insufficient validation of user arguments passed to specific CLI commands. A low-privileged attacker could exploit this by using crafted commands at the prompt, potentially leading to privilege escalation to root and execution of arbitrary commands on the underlying operating system.

Vendor
Cisco
Product
Cisco IOS XR Software
CVSS
HIGH 8.8
CISA KEV
Not listed in stored evidence
Original CVE published
2026-03-11
Original CVE updated
2026-07-01
Advisory published
2026-03-11
Advisory updated
2026-07-01

Who should care

System administrators and security professionals responsible for Cisco IOS XR Software installations should be aware of this vulnerability. Given its high CVSS score of 8.8, organizations using affected versions of Cisco IOS XR Software should prioritize patching. This vulnerability could allow an attacker with a low-privileged account to escalate privileges to root, potentially leading to full control of the affected device.

Technical summary

The vulnerability exists in the CLI of Cisco IOS XR Software due to insufficient validation of user arguments passed to specific CLI commands. An authenticated, local attacker with a low-privileged account could exploit this vulnerability by using crafted commands at the prompt. A successful exploit could allow the attacker to elevate privileges to root and execute arbitrary commands on the underlying operating system. The Common Vulnerability Scoring System (CVSS) score for this vulnerability is 8.8, indicating a high severity. The CVSS vector is CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H.

Defensive priority

This vulnerability has a high defensive priority due to its CVSS score of 8.8 and the potential for privilege escalation to root. Organizations using affected Cisco IOS XR Software versions should prioritize patching to prevent potential exploitation.

Recommended defensive actions

  • Review and apply Cisco's security advisories and patches for CVE-2026-20040.
  • Implement strict access controls and monitoring for CLI access.
  • Conduct regular vulnerability assessments and inventory checks for Cisco IOS XR Software installations.
  • Consider compensating controls such as limiting local access to critical systems.
  • Monitor system logs for suspicious CLI activity.

Evidence notes

The CVE-2026-20040 record was obtained from the official CVE.org database and the National Vulnerability Database (NVD). The vulnerability is described in Cisco's security advisory (cisco-sa-iosxr-privesc-bF8D5U4W). Cisco IOS XR Software versions prior to 25.2.21 and 25.3.1 to 25.4.2 are affected. The CWE-78 weakness is associated with this vulnerability.

Official resources

This article is AI-assisted and based on the supplied source corpus.