CVE-2024-20537: Cisco ISE Authorization Bypass Vulnerability

CVE-2024-20537 Overview

A vulnerability in the web-based management interface of Cisco Identity Services Engine (ISE) could allow an authenticated, remote attacker to bypass the authorization mechanisms for specific administrative functions. This vulnerability is due to a lack of server-side validation of Administrator permissions. An attacker could exploit this vulnerability by submitting a crafted HTTP request to an affected system. A successful exploit could allow the attacker to conduct administrative functions beyond their intended access level.

Critical Impact

An attacker with Read-Only Administrator credentials can escalate their privileges to perform unauthorized administrative actions, potentially compromising the integrity of network access control configurations and security policies managed by Cisco ISE.

Affected Products

• Cisco Identity Services Engine 3.0.0 (base and patches 1-8)
• Cisco Identity Services Engine 3.1.0 (base and patches 1-9)
• Cisco Identity Services Engine 3.2.0 (base and patches 1-6)
• Cisco Identity Services Engine 3.3.0 (base and patches 1-2)

Discovery Timeline

• November 6, 2024 - CVE-2024-20537 published to NVD
• November 22, 2024 - Last updated in NVD database

Technical Details for CVE-2024-20537

Vulnerability Analysis

This vulnerability represents an Authorization Bypass weakness (CWE-863: Incorrect Authorization) in the Cisco Identity Services Engine web-based management interface. The core issue stems from the application's failure to properly validate administrator permission levels on the server side when processing HTTP requests.

The vulnerability allows attackers holding Read-Only Administrator credentials to perform administrative functions that should be restricted to higher privilege levels. This type of authorization bypass is particularly dangerous in enterprise network access control systems like Cisco ISE, which serve as central policy decision points for network security.

The attack requires network access to the ISE management interface and valid Read-Only Administrator credentials, meaning it cannot be exploited by completely unauthenticated attackers. However, in scenarios where Read-Only credentials are more widely distributed for monitoring purposes, or if such credentials are compromised through other means, this vulnerability provides a direct path to privilege escalation.

Root Cause

The root cause of this vulnerability is the lack of server-side validation of Administrator permissions in the Cisco ISE web-based management interface. When processing administrative requests, the application fails to properly verify that the authenticated user has the appropriate privilege level to perform the requested action. Instead of enforcing role-based access controls on the server side, the application appears to rely on client-side controls or incomplete server-side checks that can be bypassed through crafted HTTP requests.

Attack Vector

The attack vector is network-based and requires an authenticated attacker with Read-Only Administrator credentials. The exploitation process involves:

1. An attacker obtains valid Read-Only Administrator credentials for the target Cisco ISE deployment
2. The attacker authenticates to the web-based management interface using these credentials
3. The attacker crafts and submits HTTP requests to administrative endpoints that should be restricted
4. Due to insufficient server-side permission validation, the ISE processes these requests despite the attacker's limited role
5. The attacker successfully executes administrative functions beyond their authorized access level

The vulnerability does not require user interaction and can be exploited remotely over the network. The attack complexity is low, as no special conditions or circumstances are required beyond possessing Read-Only credentials.

Detection Methods for CVE-2024-20537

Indicators of Compromise

• Unexpected configuration changes in Cisco ISE that cannot be attributed to authorized administrators
• Audit log entries showing administrative actions performed by Read-Only Administrator accounts
• HTTP requests to administrative API endpoints from accounts that should only have read permissions
• Anomalous activity patterns from Read-Only Administrator sessions, such as POST or PUT requests to configuration endpoints

Detection Strategies

• Review Cisco ISE audit logs for administrative actions performed by accounts with Read-Only roles
• Implement network monitoring to detect unusual HTTP request patterns to the ISE management interface
• Configure SIEM rules to alert on administrative configuration changes made by Read-Only accounts
• Monitor for crafted HTTP requests that attempt to access privileged administrative functions

Monitoring Recommendations

• Enable comprehensive audit logging on all Cisco ISE administrative interfaces
• Implement real-time alerting for any configuration modifications on ISE deployments
• Review administrator account activity regularly, particularly focusing on Read-Only accounts
• Deploy network traffic analysis to monitor management interface communications for anomalous behavior

How to Mitigate CVE-2024-20537

Immediate Actions Required

• Apply the security patches provided by Cisco as soon as possible
• Review and restrict network access to the Cisco ISE management interface to trusted networks only
• Audit all Read-Only Administrator accounts and revoke unnecessary access
• Implement additional access controls such as multi-factor authentication for administrative access
• Monitor audit logs for any signs of exploitation

Patch Information

Cisco has released security patches to address this vulnerability. Organizations should consult the Cisco Security Advisory for specific patch versions and upgrade paths for their affected ISE deployments. The advisory provides detailed information on fixed software releases for each affected version branch (3.0.x, 3.1.x, 3.2.x, and 3.3.x).

Workarounds

• Restrict access to the Cisco ISE web-based management interface to only essential personnel and trusted networks
• Implement network segmentation to limit exposure of the management interface
• Use firewall rules to restrict access to the ISE management ports from untrusted networks
• Consider implementing a jump server or VPN requirement for all administrative access to ISE
• Regularly review and minimize the number of accounts with any administrative access level

# Example: Restrict access to ISE management interface using ACLs
# Apply appropriate network access controls on network devices
# to limit management interface access to trusted administrator subnets

# Example ACL concept (syntax varies by platform):
# permit tcp 10.10.10.0/24 host <ISE_MGMT_IP> eq 443
# deny tcp any host <ISE_MGMT_IP> eq 443