CVE-2025-7776: Citrix NetScaler ADC DoS Vulnerability

CVE-2025-7776 Overview

A memory overflow vulnerability has been identified in Citrix NetScaler ADC and NetScaler Gateway that can lead to unpredictable or erroneous behavior and Denial of Service conditions. The vulnerability is exploitable when NetScaler is configured as a Gateway (VPN virtual server, ICA Proxy, CVPN, RDP Proxy) with a PCoIP Profile bound to it. This memory corruption flaw (CWE-119) allows remote attackers to trigger buffer boundary violations without requiring authentication.

Critical Impact

Unauthenticated remote attackers can exploit this memory overflow vulnerability to cause system instability, data corruption, and complete Denial of Service on affected NetScaler deployments configured with PCoIP Profiles.

Affected Products

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

Discovery Timeline

• August 26, 2025 - CVE-2025-7776 published to NVD
• September 3, 2025 - Last updated in NVD database

Technical Details for CVE-2025-7776

Vulnerability Analysis

This vulnerability stems from improper restriction of operations within the bounds of a memory buffer (CWE-119) in the NetScaler Gateway component. When NetScaler is deployed as a VPN virtual server, ICA Proxy, CVPN, or RDP Proxy with a PCoIP Profile configured, the system fails to properly validate memory boundaries during certain operations. This allows an attacker to overflow memory buffers, leading to corruption of adjacent memory regions.

The vulnerability is particularly concerning because it requires no authentication and can be exploited remotely over the network. The attack complexity is low, meaning adversaries do not need specialized conditions or preparation to launch an attack. The impact includes potential confidentiality and integrity breaches alongside a high availability impact that can result in complete service disruption.

Root Cause

The root cause of CVE-2025-7776 lies in improper buffer boundary checking within the PCoIP Profile handling routines of NetScaler Gateway. When processing PCoIP-related requests, the affected code path fails to validate that data being written to memory stays within allocated buffer boundaries. This lack of bounds checking is classified as CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer).

The vulnerability specifically manifests when the Gateway is bound to a PCoIP Profile, enabling the vulnerable code path that handles PCoIP protocol communications. Without proper validation, maliciously crafted input can overflow the buffer and corrupt adjacent memory structures.

Attack Vector

The attack can be executed remotely over the network without requiring any user interaction or prior authentication. An attacker can send specially crafted network requests to the vulnerable NetScaler Gateway service that exploits the memory overflow condition.

The attack targets the PCoIP Profile handling functionality, which is active when NetScaler is configured as a Gateway with VPN, ICA Proxy, CVPN, or RDP Proxy capabilities. By sending malformed data that exceeds expected buffer sizes, attackers can trigger memory corruption that leads to unpredictable system behavior or complete service denial.

For detailed technical information about exploitation patterns, refer to the Citrix Knowledge Base Article.

Detection Methods for CVE-2025-7776

Indicators of Compromise

• Unexpected NetScaler Gateway service crashes or restarts, particularly when PCoIP Profiles are in use
• Abnormal memory consumption patterns or memory-related error messages in system logs
• Unusual network traffic patterns targeting Gateway virtual server endpoints
• System instability or erratic behavior following processing of PCoIP-related requests

Detection Strategies

• Monitor NetScaler system logs for memory-related errors, buffer overflow warnings, or unexpected service terminations
• Implement network intrusion detection rules to identify anomalous traffic patterns targeting NetScaler Gateway services
• Deploy application-level monitoring to detect abnormal PCoIP Profile processing behavior
• Utilize SentinelOne Singularity to monitor for memory corruption attempts and abnormal process behavior on network infrastructure

Monitoring Recommendations

• Enable verbose logging on NetScaler ADC and Gateway appliances to capture detailed diagnostic information
• Configure alerts for Gateway service availability and automatic restart events
• Implement network baseline analysis to detect deviation from normal traffic patterns to Gateway endpoints
• Review system health metrics regularly, focusing on memory utilization and service stability

How to Mitigate CVE-2025-7776

Immediate Actions Required

• Review your NetScaler deployment to determine if Gateway configurations with PCoIP Profiles are in use
• Apply the latest security patches from Citrix as soon as they become available
• Consider temporarily disabling PCoIP Profiles on affected Gateway configurations if operationally feasible
• Implement network segmentation to limit exposure of vulnerable NetScaler Gateway services

Patch Information

Citrix has released a security advisory addressing this vulnerability. Administrators should consult the Citrix Knowledge Base Article CTX694938 for specific patch versions and remediation guidance. Apply the recommended updates to all affected NetScaler ADC and NetScaler Gateway deployments as a priority.

Verify that your NetScaler firmware version is listed among the patched releases in the Citrix advisory before considering remediation complete.

Workarounds

• If patches cannot be applied immediately, consider unbinding PCoIP Profiles from Gateway virtual servers as a temporary mitigation
• Restrict network access to NetScaler Gateway services using firewall rules to limit exposure to trusted networks only
• Implement Web Application Firewall (WAF) rules to filter potentially malicious requests targeting the vulnerable endpoints
• Monitor systems closely for signs of exploitation while planning patch deployment

# Check current PCoIP Profile bindings on NetScaler Gateway
show vpn vserver <vserver_name> | grep -i pcoip

# List all Gateway virtual servers to identify affected configurations
show vpn vserver

# Review Gateway configuration for PCoIP Profile usage
show run | grep -i pcoip