CVE-2026-20110: Cisco IOS XE Software DoS Vulnerability

CVE-2026-20110 Overview

A vulnerability in the CLI of Cisco IOS XE Software could allow an authenticated, local attacker to cause a denial of service (DoS) condition on an affected device. This vulnerability exists because incorrect privileges are associated with the start maintenance command. An attacker could exploit this vulnerability by accessing the management CLI of the affected device as a low-privileged user and using the start maintenance command. A successful exploit could allow the attacker to put the device in maintenance mode, which shuts down interfaces, resulting in a denial of service (DoS) condition.

Critical Impact

Successful exploitation enables low-privileged users to shut down all device interfaces by triggering maintenance mode, causing complete network disruption until an administrator manually restores operations using the stop maintenance command.

Affected Products

• Cisco IOS XE Software

Discovery Timeline

• 2026-03-25 - CVE CVE-2026-20110 published to NVD
• 2026-03-26 - Last updated in NVD database

Technical Details for CVE-2026-20110

Vulnerability Analysis

This vulnerability is classified under CWE-266 (Incorrect Privilege Assignment), indicating a fundamental flaw in how access controls are implemented for the start maintenance CLI command in Cisco IOS XE Software. The core issue stems from the maintenance mode functionality being accessible to users who should not have the authority to initiate such disruptive operations.

The maintenance mode feature is designed to allow administrators to gracefully take a device offline for scheduled maintenance activities. When activated, this mode systematically shuts down network interfaces to prevent traffic flow through the device. However, due to the privilege misconfiguration, users with minimal access rights can invoke this powerful administrative function.

The vulnerability requires local authenticated access to the device CLI, meaning an attacker must first have valid credentials and the ability to establish a management session. While this limits the attack surface compared to remote vulnerabilities, insider threats and compromised low-privilege accounts pose significant risk.

Recovery from exploitation is straightforward but requires administrator intervention. A device administrator must connect to the CLI and execute the stop maintenance command to restore normal operations and bring interfaces back online.

Root Cause

The root cause of CVE-2026-20110 is incorrect privilege assignment (CWE-266) for the start maintenance CLI command. The command is not properly restricted to administrator-level users, allowing low-privileged authenticated users to execute a function that should require elevated permissions. This represents a failure in the principle of least privilege implementation within the IOS XE command authorization framework.

Attack Vector

The attack vector requires local authenticated access to the Cisco IOS XE device CLI. An attacker with low-privilege credentials can exploit this vulnerability through the following attack flow:

1. Authenticate to the device management CLI using a low-privilege user account
2. Execute the start maintenance command at the CLI prompt
3. The device enters maintenance mode, shutting down all interfaces
4. Network traffic through the device is disrupted, causing denial of service

This is a privilege escalation attack that allows unauthorized access to administrative functionality. The attacker does not need to exploit any memory corruption or inject malicious code—they simply invoke a legitimately intended command that lacks proper access controls.

Detection Methods for CVE-2026-20110

Indicators of Compromise

• Unexpected maintenance mode activation events in device logs
• Interface shutdown events without corresponding administrative change requests
• CLI access logs showing low-privilege users executing the start maintenance command
• Network monitoring alerts indicating sudden loss of connectivity through affected devices

Detection Strategies

• Monitor AAA accounting logs for start maintenance command execution by non-administrator users
• Configure syslog monitoring to alert on maintenance mode state changes
• Implement SNMP traps for interface status changes that correlate with unauthorized CLI access
• Review authentication logs for unusual low-privilege account activity on network infrastructure

Monitoring Recommendations

• Enable command accounting on all Cisco IOS XE devices to track CLI command execution
• Establish baseline alerting for maintenance mode transitions outside scheduled windows
• Deploy network monitoring to detect unexpected interface state changes across critical infrastructure
• Correlate CLI access events with change management tickets to identify unauthorized activity

How to Mitigate CVE-2026-20110

Immediate Actions Required

• Apply the security patch from Cisco as soon as available
• Review and restrict CLI access for low-privilege user accounts
• Implement privilege level restrictions using command authorization with AAA
• Enable enhanced logging and monitoring for maintenance mode commands
• Document recovery procedures using the stop maintenance command for rapid incident response

Patch Information

Cisco has released a security advisory addressing this vulnerability. Administrators should consult the Cisco Security Advisory for detailed patch information and affected software versions. Apply the recommended software updates following your organization's change management procedures.

Workarounds

• Configure command authorization using AAA to restrict the start maintenance command to administrator privilege levels only
• Implement role-based access control (RBAC) to limit CLI command access based on user roles
• Use privilege level configuration to prevent low-privilege users from accessing maintenance commands
• Consider restricting management CLI access to trusted jump hosts or management networks

# Example AAA command authorization configuration
aaa authorization commands 15 default group tacacs+ local
privilege exec level 15 start maintenance