CVE-2024-20316: Cisco IOS XE Auth Bypass Vulnerability

CVE-2024-20316 Overview

A vulnerability in the data model interface (DMI) services of Cisco IOS XE Software could allow an unauthenticated, remote attacker to access resources that should have been protected by a configured IPv4 access control list (ACL). This vulnerability is due to improper handling of error conditions when a successfully authorized device administrator updates an IPv4 ACL using the NETCONF or RESTCONF protocol, and the update would reorder access control entries (ACEs) in the updated ACL.

Critical Impact

An attacker could exploit this vulnerability by accessing resources that should have been protected across an affected device, effectively bypassing network security controls designed to restrict unauthorized access.

Affected Products

• Cisco IOS XE versions 16.3.1 through 16.12.11
• Cisco IOS XE versions 17.1.1 through 17.9.4a
• Cisco IOS XE versions 17.10.1 through 17.12.2a

Discovery Timeline

• March 27, 2024 - CVE-2024-20316 published to NVD
• July 30, 2025 - Last updated in NVD database

Technical Details for CVE-2024-20316

Vulnerability Analysis

This vulnerability resides in the Data Model Interface (DMI) services component of Cisco IOS XE Software, which handles programmatic configuration management through NETCONF and RESTCONF protocols. The flaw manifests when an authorized administrator performs legitimate ACL updates that trigger a reordering of Access Control Entries (ACEs) within the ACL configuration.

The core issue relates to CWE-390 (Detection of Error Condition Without Action), where the software fails to properly respond to error conditions that occur during ACL modification operations. When ACE reordering is triggered during an update, the system encounters an error state but does not take appropriate corrective action, resulting in the ACL not being properly enforced.

Root Cause

The root cause of this vulnerability is improper error handling within the DMI services component. When NETCONF or RESTCONF configuration updates cause ACEs to be reordered within an IPv4 ACL, the system encounters an error condition but fails to either:

1. Properly rollback the configuration to a known-good state
2. Alert administrators to the failure condition
3. Maintain the enforcement of the existing ACL rules during the transition

This error detection without action allows the ACL to enter an inconsistent state where traffic filtering rules may not be applied as intended, permitting unauthorized network access.

Attack Vector

The attack vector for this vulnerability is network-based and does not require authentication for exploitation. The exploitation scenario involves:

1. An authorized administrator legitimately updates an IPv4 ACL using NETCONF or RESTCONF protocols
2. The update triggers a reordering of ACEs within the ACL
3. The DMI services encounter an error condition but fail to handle it properly
4. The ACL enters a degraded enforcement state
5. An unauthenticated remote attacker can then access resources that should have been blocked by the ACL

This is particularly concerning because the vulnerability is triggered by normal administrative operations, making it difficult to predict when the system might become vulnerable. The attacker does not need to interact with the vulnerable system directly to trigger the condition—they simply need to time their access attempts to coincide with periods when ACL enforcement may be compromised.

Detection Methods for CVE-2024-20316

Indicators of Compromise

• Unexpected network traffic reaching resources that should be blocked by configured ACLs
• NETCONF or RESTCONF session logs showing ACL modification operations followed by configuration inconsistencies
• Discrepancies between the intended ACL configuration and actual traffic behavior
• System logs indicating DMI services errors during ACL update operations

Detection Strategies

• Monitor NETCONF and RESTCONF sessions for ACL modification operations, particularly those that may trigger ACE reordering
• Implement network traffic monitoring to detect unauthorized access attempts to ACL-protected resources
• Configure alerting for configuration changes to IPv4 ACLs through programmatic interfaces
• Perform regular validation of ACL enforcement by testing access to protected resources after configuration changes

Monitoring Recommendations

• Enable detailed logging for DMI services and NETCONF/RESTCONF operations on affected Cisco IOS XE devices
• Implement network-based intrusion detection to identify traffic patterns inconsistent with configured ACL policies
• Establish baseline traffic patterns to protected resources and alert on deviations
• Review ACL hit counters periodically to verify rules are being applied as expected

How to Mitigate CVE-2024-20316

Immediate Actions Required

• Review the Cisco Security Advisory for specific guidance on affected versions and available patches
• Audit all Cisco IOS XE devices running versions 16.3.x through 17.12.x to determine exposure
• Implement additional network segmentation or firewall rules as compensating controls
• Avoid making ACL changes via NETCONF/RESTCONF that would cause ACE reordering until patched

Patch Information

Cisco has released security updates to address this vulnerability. Administrators should consult the Cisco Security Advisory for detailed information on fixed software releases and upgrade paths specific to their deployment. The advisory includes a Software Checker tool to help identify whether specific IOS XE versions are affected.

Workarounds

• Use CLI-based ACL management instead of NETCONF/RESTCONF for configuration changes that may reorder ACEs
• Implement secondary ACL protection at network perimeter devices to provide defense-in-depth
• Verify ACL enforcement after any programmatic configuration changes by testing access to protected resources
• Consider disabling NETCONF and RESTCONF services if not operationally required until patches can be applied

# Verify NETCONF/RESTCONF configuration status
show running-config | include netconf\|restconf

# Review current ACL configuration
show ip access-lists

# Check DMI services status
show platform software yang-management process state

# Disable RESTCONF if not required (example)
configure terminal
no restconf
end