CVE-2026-20037: Cisco UCS Manager Privilege Escalation Flaw

CVE-2026-20037 Overview

A privilege escalation vulnerability exists in the NX-OS CLI privilege levels of Cisco UCS Manager Software. This vulnerability allows an authenticated, local attacker with read-only privileges to modify files and perform unauthorized actions on an affected system.

The vulnerability exists because unnecessary privileges are granted to the user. An attacker could exploit this vulnerability by authenticating to a device as a read-only user and connecting to the NX-OS CLI. A successful exploit could allow the attacker to create or overwrite files in the file system or perform limited privileged actions on an affected device.

Critical Impact

Authenticated attackers with read-only access can escalate privileges to modify files and perform unauthorized actions, potentially compromising system integrity.

Affected Products

• Cisco UCS Manager Software (NX-OS CLI component)

Discovery Timeline

• 2026-02-25 - CVE-2026-20037 published to NVD
• 2026-02-25 - Last updated in NVD database

Technical Details for CVE-2026-20037

Vulnerability Analysis

This vulnerability is classified under CWE-250 (Execution with Unnecessary Privileges). The issue stems from improper privilege assignment within the NX-OS CLI component of Cisco UCS Manager Software, where read-only users are inadvertently granted elevated capabilities that should be restricted to higher-privilege accounts.

When a user authenticates to the system with read-only credentials, the NX-OS CLI fails to properly enforce privilege boundaries, allowing the user to perform actions beyond their intended authorization scope. This represents a classic privilege escalation scenario where the principle of least privilege is violated.

Root Cause

The root cause of CVE-2026-20037 is the assignment of unnecessary privileges to read-only user accounts within the NX-OS CLI. The privilege enforcement mechanism does not adequately restrict file system operations and certain privileged actions for users who should only have observational access to the system.

Attack Vector

The attack requires local access to the affected system and valid read-only credentials. An attacker would:

1. Authenticate to the Cisco UCS Manager device using read-only credentials
2. Connect to the NX-OS CLI interface
3. Leverage the excessive privileges to create or overwrite files in the file system
4. Potentially perform limited privileged actions that could affect device configuration or operation

The local attack vector and requirement for authentication reduce the immediate risk, but the ability to modify files could lead to further compromise, including persistence mechanisms or configuration tampering.

Detection Methods for CVE-2026-20037

Indicators of Compromise

• Unexpected file modifications or new files created by read-only user accounts
• Audit logs showing privileged actions performed by users with read-only roles
• Configuration changes attributed to accounts that should lack write permissions
• Unusual NX-OS CLI activity patterns from read-only accounts

Detection Strategies

• Monitor NX-OS audit logs for file system write operations by read-only users
• Implement file integrity monitoring on critical system directories
• Review authentication logs for suspicious NX-OS CLI sessions
• Alert on any configuration modifications from accounts without administrative privileges

Monitoring Recommendations

• Enable comprehensive logging for all NX-OS CLI sessions
• Configure SIEM rules to correlate user privilege levels with action types
• Regularly audit user permissions and compare against expected baselines
• Monitor for unexpected privilege escalation indicators in system logs

How to Mitigate CVE-2026-20037

Immediate Actions Required

• Review and audit all read-only user accounts on affected Cisco UCS Manager systems
• Limit physical and network access to affected devices to trusted personnel only
• Monitor NX-OS CLI activity for suspicious behavior from low-privilege accounts
• Apply vendor patches as soon as they become available from Cisco

Patch Information

Cisco has published a security advisory addressing this vulnerability. System administrators should review the Cisco Security Advisory for detailed patch information and upgrade guidance. Follow Cisco's recommended upgrade path to apply security fixes that properly enforce privilege separation in the NX-OS CLI.

Workarounds

• Restrict physical and network access to the NX-OS CLI to essential personnel only
• Implement additional access controls at the network layer to limit CLI access
• Audit and remove unnecessary read-only accounts until patches are applied
• Consider implementing multi-factor authentication for CLI access where supported