CVE-2024-20510: Cisco IOS XE Auth Bypass Vulnerability

CVE-2024-20510 Overview

A critical authorization bypass vulnerability exists in the Central Web Authentication (CWA) feature of Cisco IOS XE Software for Wireless Controllers. This vulnerability allows an unauthenticated attacker with adjacent network access to bypass the pre-authentication access control list (ACL), potentially gaining unauthorized access to protected network resources before completing user authentication.

The vulnerability stems from a logic error in how the pre-authentication ACL is activated when received from the authentication, authorization, and accounting (AAA) server. An attacker can exploit this flaw by connecting to a wireless network configured for CWA and transmitting traffic through an affected device that should normally be blocked by the configured ACL prior to user authentication.

Critical Impact

Successful exploitation allows attackers to bypass ACL protections and access trusted networks protected by affected wireless controllers without completing authentication, potentially compromising network segmentation and security controls.

Affected Products

• Cisco IOS XE Software versions 16.3.1 through 16.12.11 for Wireless Controllers
• Cisco IOS XE Software versions 17.1.1 through 17.9.5b for Wireless Controllers
• Cisco IOS XE Software versions 17.10.1 through 17.13.1a for Wireless Controllers

Discovery Timeline

• September 25, 2024 - CVE-2024-20510 published to NVD
• October 3, 2024 - Last updated in NVD database

Technical Details for CVE-2024-20510

Vulnerability Analysis

This vulnerability is classified as CWE-863 (Incorrect Authorization), affecting the Central Web Authentication feature in Cisco IOS XE Wireless Controllers. The flaw occurs during the pre-authentication phase when a wireless client connects to a network configured for CWA.

In a properly functioning CWA deployment, when a client connects to the wireless network, the wireless controller applies a pre-authentication ACL received from the AAA server. This ACL is designed to restrict the client's network access until they complete web-based authentication. Only specific traffic (typically DNS and HTTP to the authentication portal) should be permitted.

The vulnerability allows an attacker on an adjacent network segment to send traffic that should be denied by the pre-authentication ACL. Because the logic error prevents proper ACL activation, this traffic is incorrectly permitted through the wireless controller, granting the attacker access to protected network resources.

Root Cause

The root cause is a logic error in the Cisco IOS XE software's handling of pre-authentication ACLs received from the AAA server. When the wireless controller receives the ACL configuration during the CWA authentication flow, the ACL is not properly activated or applied to the client session. This implementation flaw creates a window where traffic that should be blocked by the pre-authentication ACL is instead allowed through, effectively negating the access controls designed to restrict unauthenticated users.

Attack Vector

The attack requires adjacent network access, meaning the attacker must be within wireless range of the target network or otherwise connected to the same network segment as the vulnerable wireless controller. The attack flow involves:

1. The attacker associates with a wireless network configured for Central Web Authentication
2. The wireless controller receives a pre-authentication ACL from the AAA server
3. Due to the logic error, the ACL is not properly activated
4. The attacker sends traffic that should be denied by the pre-authentication ACL
5. The traffic is incorrectly permitted, bypassing authentication requirements
6. The attacker gains unauthorized access to network resources that should be protected

This vulnerability requires no authentication and no user interaction, making it particularly dangerous in environments where CWA is used to protect sensitive network resources.

Detection Methods for CVE-2024-20510

Indicators of Compromise

• Unexpected network traffic from wireless clients that have not completed web authentication
• Authentication logs showing incomplete CWA sessions followed by internal network access
• AAA server logs indicating pre-authentication ACL assignments that don't correlate with expected traffic patterns
• Network traffic analysis revealing connections to internal resources from unauthenticated wireless clients

Detection Strategies

• Monitor wireless controller logs for CWA authentication flow anomalies and incomplete authentication sequences
• Implement network traffic analysis to detect unauthorized access attempts from wireless client IP ranges before authentication completion
• Configure alerts for traffic from wireless client VLANs to sensitive internal resources that bypass expected authentication patterns
• Review AAA server logs for discrepancies between ACL assignments and actual traffic flows

Monitoring Recommendations

• Enable detailed logging on Cisco wireless controllers for CWA authentication events
• Deploy network detection and response (NDR) solutions to monitor east-west traffic from wireless segments
• Implement SIEM correlation rules to detect authentication bypass patterns
• Conduct regular audits of wireless controller configurations and ACL enforcement

How to Mitigate CVE-2024-20510

Immediate Actions Required

• Review Cisco's security advisory for the latest fixed software versions and upgrade affected wireless controllers
• Audit wireless networks using CWA to identify potentially affected deployments
• Implement additional network segmentation controls to limit the impact of potential ACL bypass
• Monitor for suspicious traffic patterns from unauthenticated wireless clients

Patch Information

Cisco has released security patches addressing this vulnerability. Organizations should consult the Cisco Security Advisory for specific fixed software versions corresponding to their current deployment. Given the extensive list of affected versions spanning from 16.3.1 through 17.13.1a, administrators should identify their current IOS XE version and upgrade to the appropriate fixed release.

Workarounds

• Consider implementing additional Layer 3 ACLs on upstream network devices to provide defense-in-depth until patches can be applied
• Where feasible, evaluate alternative authentication methods such as 802.1X that may not be affected by this specific vulnerability
• Implement strict network segmentation to limit what resources wireless clients can access even if ACL bypass occurs
• Deploy additional monitoring and alerting for unauthorized network access from wireless segments

# Example: Verify current IOS XE version and CWA configuration
show version | include IOS XE
show wireless profile policy detailed
show wireless wlan summary
show ip access-lists

# Verify AAA configuration for CWA
show aaa servers
show radius statistics