CVE-2024-8535 Overview
CVE-2024-8535 is a privilege escalation vulnerability affecting Citrix NetScaler ADC and NetScaler Gateway appliances. This vulnerability allows authenticated users to access unintended user capabilities when the appliance is configured as a Gateway (SSL VPN, ICA Proxy, CVPN, RDP Proxy) or as an Auth Server (AAA Vserver) with KCDAccount configuration for Kerberos SSO to access backend resources.
Critical Impact
Authenticated attackers can leverage this vulnerability to gain access to capabilities beyond their authorized permissions, potentially compromising the security boundary between users in enterprise environments utilizing Kerberos Single Sign-On.
Affected Products
- Citrix NetScaler Application Delivery Controller (all editions including FIPS and NDCPP)
- Citrix NetScaler Gateway
- Appliances configured with KCDAccount for Kerberos SSO
Discovery Timeline
- 2024-11-12 - CVE-2024-8535 published to NVD
- 2025-07-25 - Last updated in NVD database
Technical Details for CVE-2024-8535
Vulnerability Analysis
This vulnerability is classified under CWE-552 (Files or Directories Accessible to External Parties), indicating an improper access control issue within the Kerberos Constrained Delegation (KCD) implementation. The flaw exists in how NetScaler manages user capability boundaries when KCDAccount configurations are in place for Kerberos SSO authentication to backend resources.
The vulnerability specifically manifests when NetScaler appliances are deployed in one of two configurations: as a Gateway solution (supporting SSL VPN, ICA Proxy, CVPN, or RDP Proxy) or as an Authentication Server (AAA Vserver). In both scenarios, the presence of KCDAccount configuration for Kerberos SSO creates the vulnerable condition.
Root Cause
The root cause lies in improper authorization enforcement within the NetScaler's Kerberos delegation mechanism. When authenticated users interact with the appliance configured for Kerberos SSO, the system fails to properly restrict access to user capabilities, allowing authenticated users to access functionality intended for other user contexts or privilege levels.
Attack Vector
The attack requires network access and valid authentication credentials to the NetScaler appliance. Once authenticated, an attacker can exploit the misconfiguration in the KCDAccount and Kerberos SSO implementation to gain elevated privileges or access capabilities assigned to other users.
The exploitation path involves:
- An attacker authenticates to the vulnerable NetScaler Gateway or AAA Vserver
- The appliance processes the authentication through the Kerberos SSO mechanism
- Due to improper capability boundary enforcement, the authenticated user gains access to unintended capabilities
- The attacker can then leverage these elevated capabilities to access backend resources beyond their authorization
No public exploit code is currently available for this vulnerability, and it has not been added to CISA's Known Exploited Vulnerabilities catalog.
Detection Methods for CVE-2024-8535
Indicators of Compromise
- Unusual access patterns from authenticated users to backend resources that exceed their normal authorization scope
- Unexpected Kerberos ticket requests or delegation activities in authentication logs
- Anomalous user capability changes or access to administrative functions by non-privileged accounts
- Authentication events showing users accessing resources outside their typical role boundaries
Detection Strategies
- Review NetScaler Gateway and AAA Vserver logs for authentication anomalies and unauthorized capability access
- Monitor Kerberos ticket-granting and delegation activities for suspicious patterns
- Implement user behavior analytics to detect users accessing resources outside their normal scope
- Audit KCDAccount configurations and associated user capability assignments
Monitoring Recommendations
- Enable detailed logging for all authentication and authorization events on NetScaler appliances
- Configure alerts for unusual access patterns to backend resources through Kerberos SSO
- Regularly audit user capability assignments and compare against expected baselines
- Implement SIEM correlation rules to detect privilege escalation attempts through the Kerberos SSO pathway
How to Mitigate CVE-2024-8535
Immediate Actions Required
- Review and inventory all NetScaler ADC and NetScaler Gateway appliances with KCDAccount configurations for Kerberos SSO
- Apply the security patches provided by Citrix as documented in the security bulletin
- Audit user capability assignments and verify proper access controls are enforced
- Monitor authentication logs for signs of exploitation while patching is underway
Patch Information
Citrix has released security patches addressing this vulnerability. Organizations should consult the Citrix Security Bulletin CTX691608 for specific version information and patch download instructions. Patching should be prioritized for all appliances configured as Gateways or AAA Vservers with Kerberos SSO enabled.
Workarounds
- If immediate patching is not possible, consider temporarily disabling KCDAccount configurations where feasible
- Implement additional network segmentation between the NetScaler appliance and backend resources
- Enforce stricter authentication requirements and monitor all authenticated sessions closely
- Review and restrict user capabilities to the minimum required for business operations
# Verify KCDAccount configuration status on NetScaler
show aaa kcdAccount
# Review AAA Vserver configuration
show authentication vserver
# Check Gateway configuration for Kerberos SSO
show vpn vserver
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
