CVE-2026-20099: Cisco FXOS & UCS Manager Privilege Escalation

CVE-2026-20099 Overview

A command injection vulnerability exists in the web-based management interface of Cisco FXOS Software and Cisco UCS Manager Software. This vulnerability could allow an authenticated, local attacker with administrative privileges to perform command injection attacks on an affected system and elevate privileges to root.

The vulnerability is due to insufficient input validation of command arguments supplied by the user. An attacker could exploit this vulnerability by authenticating to a device and submitting crafted input to the affected command. A successful exploit could allow the attacker to execute arbitrary commands on the underlying operating system of the affected device with root-level privileges.

Critical Impact

An attacker with administrative access can achieve root-level privilege escalation through command injection, potentially gaining complete control of the underlying operating system.

Affected Products

• Cisco FXOS Software
• Cisco UCS Manager Software

Discovery Timeline

• 2026-02-25 - CVE-2026-20099 published to NVD
• 2026-02-25 - Last updated in NVD database

Technical Details for CVE-2026-20099

Vulnerability Analysis

This vulnerability falls under CWE-78 (Improper Neutralization of Special Elements used in an OS Command), commonly known as OS Command Injection. The root issue lies in the web-based management interface's failure to properly sanitize user-supplied input before incorporating it into operating system commands.

The local attack vector requires the attacker to have existing administrative access to the device. While this raises the barrier to exploitation, the impact remains significant as it enables privilege escalation from administrator to root. This distinction is important because even administrative accounts in Cisco FXOS and UCS Manager are typically constrained to specific management functions, while root access provides unrestricted control over the underlying operating system.

Root Cause

The vulnerability stems from insufficient input validation of command arguments supplied by users through the web-based management interface. When processing certain administrative commands, the affected software fails to properly sanitize special characters and command sequences that could be interpreted by the underlying shell.

This improper neutralization allows an attacker to inject arbitrary operating system commands by embedding malicious payload within legitimate command parameters. The injected commands execute with the elevated privileges of the management interface process, which in this case runs with root-level access.

Attack Vector

The attack requires local access to the device and valid administrative credentials. Once authenticated to the web-based management interface, an attacker can craft malicious input containing shell metacharacters or command separators (such as ;, |, &, or backticks) within command arguments.

When the vulnerable function processes this crafted input without proper sanitization, the embedded commands are passed directly to the operating system shell. Since the management interface operates with root privileges, the injected commands execute with full root-level access, enabling complete system compromise.

The attacker could leverage this to install persistent backdoors, exfiltrate sensitive configuration data, pivot to other network infrastructure, or disrupt operations by modifying critical system files.

Detection Methods for CVE-2026-20099

Indicators of Compromise

• Unusual administrative session activity with malformed or suspicious command parameters
• Unexpected processes spawned by the web management interface with root privileges
• Anomalous shell command execution patterns in system logs
• Modifications to system files or configurations outside of normal administrative workflows

Detection Strategies

• Monitor authentication logs for administrative sessions followed by unusual command execution patterns
• Implement logging and alerting on web management interface commands containing shell metacharacters
• Deploy file integrity monitoring on critical system binaries and configuration files
• Analyze network traffic for anomalous administrative interface usage patterns

Monitoring Recommendations

• Enable comprehensive logging for the web-based management interface
• Configure SIEM rules to detect command injection patterns in administrative interface logs
• Monitor for unexpected privilege escalation events or root shell spawning
• Establish baseline behavior for administrative sessions and alert on deviations

How to Mitigate CVE-2026-20099

Immediate Actions Required

• Review the Cisco Security Advisory for specific patch information and affected versions
• Restrict administrative access to the web-based management interface to trusted users only
• Implement network segmentation to limit access to management interfaces
• Enable comprehensive audit logging for all administrative actions
• Monitor administrative sessions for suspicious activity patterns

Patch Information

Cisco has released security updates to address this vulnerability. Organizations should consult the Cisco Security Advisory for detailed information about affected software versions and corresponding fixed releases. Apply the appropriate patches as soon as possible following your organization's change management procedures.

Workarounds

• Limit administrative interface access to only essential personnel
• Implement multi-factor authentication for administrative access where supported
• Use out-of-band management networks to isolate administrative traffic
• Deploy additional monitoring on management interface access points
• Consider disabling web-based management and using alternative CLI-based administration where feasible

# Network segmentation example - restrict management interface access
# Configure ACLs to limit access to management interfaces from trusted subnets only
# Example: Allow only management network 10.0.100.0/24 to access the management interface

# On perimeter firewall or network device
access-list MGMT-ACL permit ip 10.0.100.0 0.0.0.255 host <management-interface-ip>
access-list MGMT-ACL deny ip any host <management-interface-ip> log