CVE-2023-6549 in NetScaler ADC
Summary
by MITRE • 01/17/2024
Improper Restriction of Operations within the Bounds of a Memory Buffer in NetScaler ADC and NetScaler Gateway allows Unauthenticated Denial of Service and Out-Of-Bounds Memory Read
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Analysis
by VulDB Data Team • 02/26/2026
The vulnerability identified as CVE-2023-6549 represents a critical flaw in Citrix NetScaler ADC and NetScaler Gateway products that stems from improper restriction of operations within memory buffer boundaries. This issue affects the fundamental memory management mechanisms within the affected systems, creating a pathway for malicious actors to exploit memory access violations that can result in system instability and service disruption. The vulnerability specifically targets the buffer handling routines that process incoming network requests, where insufficient bounds checking allows attackers to manipulate memory access patterns beyond allocated buffer limits. This flaw exists in the core networking and application delivery components of Citrix NetScaler appliances, making it particularly dangerous as it impacts the foundational infrastructure that many organizations rely upon for secure network access and application delivery.
The technical implementation of this vulnerability manifests through out-of-bounds memory read operations that occur when the NetScaler appliance processes malformed network packets or requests. Attackers can craft specific payloads that trigger memory access violations by manipulating input parameters that are processed by the affected buffer handling code. The flaw does not require authentication credentials to exploit, making it particularly dangerous as any external entity can potentially initiate the attack without prior access to the system. This unauthenticated nature aligns with attack patterns commonly associated with network-level denial of service attacks and represents a significant weakness in the system's defensive posture against unauthorized access attempts. The vulnerability operates at the memory management level, where standard input validation mechanisms fail to properly constrain memory access operations, allowing for arbitrary memory reads that can expose sensitive information or cause system crashes.
The operational impact of CVE-2023-6549 extends beyond simple service disruption to encompass potential information disclosure and system instability that can cascade across network infrastructures. Organizations utilizing NetScaler ADC and Gateway appliances face immediate risks including unauthorized denial of service attacks that can render critical network services unavailable to legitimate users. The out-of-bounds memory reads may potentially expose sensitive data stored in memory, including configuration details, user credentials, or application data that could be leveraged for further exploitation attempts. This vulnerability directly impacts the availability and integrity of network services, creating operational challenges for organizations that depend on these appliances for secure remote access and application delivery. The attack surface is particularly broad as these appliances are commonly deployed in enterprise environments where they serve as critical gateways for accessing internal resources, making successful exploitation a significant threat to business continuity and information security.
Mitigation strategies for CVE-2023-6549 should prioritize immediate patch deployment from Citrix as the primary remediation approach, following the vendor's security advisory guidance. Organizations must implement network segmentation and access controls to limit exposure of vulnerable NetScaler appliances to untrusted networks while monitoring for potential exploitation attempts. The implementation of intrusion detection systems can help identify suspicious traffic patterns that may indicate exploitation attempts, particularly focusing on malformed packets that could trigger the buffer overflow conditions. Network administrators should also consider implementing rate limiting and connection throttling mechanisms to reduce the effectiveness of denial of service attacks while monitoring system logs for unusual memory access patterns. This vulnerability demonstrates the importance of maintaining up-to-date security patches and implementing comprehensive network monitoring solutions as part of a defense-in-depth strategy. Organizations should also conduct thorough vulnerability assessments to identify all instances of affected NetScaler appliances within their infrastructure and prioritize remediation efforts based on risk exposure and business criticality.
This vulnerability aligns with CWE-129 which addresses improper restriction of operations within the bounds of a memory buffer, and represents a clear example of how insufficient input validation can lead to memory safety issues. From an ATT&CK perspective, this vulnerability maps to techniques involving denial of service and privilege escalation through memory corruption, with potential for information gathering through memory disclosure. The vulnerability's classification as unauthenticated and remote in nature places it within the category of high-impact threats that require immediate attention and remediation to prevent exploitation by threat actors. Organizations should also consider implementing additional security controls such as application firewalls and network access control lists to provide additional layers of protection against similar memory-based vulnerabilities.