CVE-2024-5491: Citrix NetScaler ADC DoS Vulnerability

CVE-2024-5491 Overview

CVE-2024-5491 is a Denial of Service vulnerability affecting Citrix NetScaler ADC and NetScaler Gateway appliances. This vulnerability allows an unauthenticated attacker on an adjacent network to disrupt service availability by overwhelming the affected systems, potentially causing significant operational impact for organizations relying on these critical network infrastructure components.

Critical Impact

Successful exploitation of this vulnerability can result in a Denial of Service condition affecting NetScaler ADC and Gateway appliances, disrupting network traffic management, load balancing, and secure remote access capabilities for enterprise environments.

Affected Products

• Citrix NetScaler Application Delivery Controller (ADC)
• Citrix NetScaler Gateway
• NetScaler ADC FIPS and NDCPP editions

Discovery Timeline

• July 10, 2024 - CVE-2024-5491 published to NVD
• July 25, 2025 - Last updated in NVD database

Technical Details for CVE-2024-5491

Vulnerability Analysis

This Denial of Service vulnerability exists within the NetScaler ADC and NetScaler Gateway products from Citrix. The vulnerability can be exploited by an attacker positioned on an adjacent network segment without requiring authentication or user interaction. While the specific technical mechanism has not been fully disclosed by Citrix, the attack has the potential to cause high impact to both confidentiality and availability of the affected systems, with limited impact on integrity.

The vulnerability affects multiple editions of NetScaler ADC, including standard, FIPS-compliant, and NDCPP-certified deployments, as well as NetScaler Gateway installations. Organizations using these products for application delivery, load balancing, or secure remote access are potentially at risk if an attacker gains access to an adjacent network segment.

Root Cause

The specific root cause of CVE-2024-5491 has not been publicly disclosed by Citrix. The vulnerability is categorized under NVD-CWE-noinfo, indicating that detailed weakness information is not available. Based on the Denial of Service classification, the vulnerability likely involves improper handling of network requests or resource management that can be triggered by malformed or excessive traffic from an adjacent network.

Attack Vector

The attack vector for CVE-2024-5491 requires the attacker to be on an adjacent network (such as the same LAN segment or connected via VPN) to the vulnerable NetScaler appliance. No authentication is required, and the attack can be executed without any user interaction, making it relatively straightforward to exploit once network proximity is achieved.

The adjacent network requirement means that while remote exploitation over the internet is not directly possible, an attacker who has compromised any system on the same network segment as the NetScaler appliance could leverage this vulnerability to disrupt critical network infrastructure.

Detection Methods for CVE-2024-5491

Indicators of Compromise

• Unexpected service interruptions or crashes on NetScaler ADC or Gateway appliances
• Unusual network traffic patterns originating from adjacent network segments targeting NetScaler management interfaces
• Increased resource utilization (CPU, memory) on NetScaler appliances without corresponding legitimate traffic increases
• System logs indicating repeated connection attempts or malformed requests from internal network sources

Detection Strategies

• Monitor NetScaler appliance health metrics and configure alerts for abnormal resource consumption patterns
• Implement network traffic analysis to detect anomalous traffic patterns from adjacent network segments targeting NetScaler services
• Deploy intrusion detection systems (IDS) with signatures updated to detect DoS attack patterns against Citrix products
• Review NetScaler system logs regularly for signs of exploitation attempts or service degradation

Monitoring Recommendations

• Enable enhanced logging on NetScaler appliances to capture detailed connection and request information
• Configure SIEM integration to correlate NetScaler events with network traffic data for comprehensive visibility
• Establish baseline performance metrics for NetScaler appliances to facilitate rapid detection of anomalies
• Implement network segmentation monitoring to identify unauthorized access attempts to NetScaler-adjacent network segments

How to Mitigate CVE-2024-5491

Immediate Actions Required

• Apply the security patches released by Citrix as outlined in the Citrix Security Bulletin CTX677944
• Review network segmentation to limit which systems have adjacent network access to NetScaler appliances
• Audit network access controls to ensure only authorized systems can communicate with NetScaler management interfaces
• Implement rate limiting where possible to mitigate potential DoS attack impact

Patch Information

Citrix has released security updates to address CVE-2024-5491. Organizations should consult the Citrix Security Bulletin for specific version information and download links for the applicable patches. The bulletin covers both CVE-2024-5491 and the related CVE-2024-5492 vulnerability.

Ensure all NetScaler ADC and NetScaler Gateway appliances are updated to the patched versions specified in the security bulletin. Priority should be given to internet-facing and business-critical deployments.

Workarounds

• Implement strict network segmentation to limit adjacent network access to NetScaler appliances to only essential systems
• Configure firewall rules to restrict traffic to NetScaler services from untrusted or unnecessary network segments
• Enable rate limiting on network devices protecting NetScaler appliances to reduce the impact of potential DoS attacks
• Consider deploying additional network monitoring at segments adjacent to NetScaler appliances to detect exploitation attempts early

# Example: Verify NetScaler firmware version via CLI
show ns version

# Check for available updates and current patch level
show ns hardware