CVE-2013-6940 in NetScaler
Summary
by MITRE
Citrix NetScaler Application Delivery Controller (ADC) 9.3.x before 9.3-64.4, 10.0 before 10.0-77.5, and 10.1 before 10.1-118.7 logs user credentials, which allows attackers to obtain sensitive information via unspecified vectors.
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Analysis
by VulDB Data Team • 05/07/2026
The Citrix NetScaler Application Delivery Controller ADC vulnerability identified as CVE-2013-6940 represents a critical security flaw in authentication logging mechanisms that affects multiple versions of the NetScaler platform. This vulnerability specifically targets the logging functionality of the ADC appliance, where user credentials are being recorded in plain text within log files, creating an exploitable condition that adversaries can leverage to gain unauthorized access to sensitive authentication information. The affected versions include Citrix NetScaler ADC 9.3.x prior to 9.3-64.4, 10.0 prior to 10.0-77.5, and 10.1 prior to 10.1-118.7, indicating this flaw spans across several major release lines and has persisted for an extended period. The vulnerability falls under the category of improper logging and monitoring as classified by CWE-778, which specifically addresses the logging of sensitive information without proper protection mechanisms.
The technical implementation flaw lies in the ADC's logging subsystem where authentication credentials are being captured and stored in log files without adequate sanitization or encryption measures. This occurs during normal operational procedures when user authentication attempts are processed through the ADC appliance, with the system failing to distinguish between legitimate operational logging requirements and sensitive credential data that should be protected from unauthorized access. The unspecified vectors mentioned in the description suggest that attackers can potentially access these credential logs through various attack surfaces including direct file system access, network-based log retrieval mechanisms, or through compromised administrative accounts that have access to the logging infrastructure. This vulnerability directly impacts the principle of least privilege and violates fundamental security practices around credential protection and audit logging.
The operational impact of this vulnerability extends far beyond simple credential theft, as it creates a persistent backdoor for attackers to maintain long-term access to the compromised environment. Once attackers obtain these logged credentials, they can leverage them to gain administrative access to the NetScaler appliance itself, potentially leading to complete compromise of the application delivery infrastructure. The implications are particularly severe because the NetScaler ADC serves as a critical component in enterprise network security, often handling SSL termination, load balancing, and application delivery functions that are essential for business operations. Attackers can use these stolen credentials to perform man-in-the-middle attacks, modify traffic routing, or establish persistent access points within the network infrastructure. The vulnerability also creates challenges for incident response teams as the compromised credentials may have been used across multiple systems and applications, potentially leading to lateral movement within the network and extended attack surfaces.
Mitigation strategies for this vulnerability require immediate implementation of security patches provided by Citrix, which would address the root cause by modifying the logging behavior to prevent credential exposure. Organizations should also implement comprehensive log monitoring and access controls to detect unauthorized access to credential logs, while establishing strict file system permissions and encryption measures for log storage. The remediation process must include comprehensive vulnerability assessments to identify any previously compromised credentials that may have been exposed through this vulnerability. Security teams should also consider implementing additional authentication controls such as multi-factor authentication for administrative access, regular credential rotation, and enhanced monitoring of administrative activities within the NetScaler environment. This vulnerability aligns with ATT&CK techniques related to credential access and privilege escalation, specifically targeting the T1078 and T1566 tactics that involve gaining access to valid credentials and using them for unauthorized access to systems and networks. Organizations should also review their logging and monitoring configurations to ensure that sensitive information is not being captured in clear text within any system logs, aligning with security best practices outlined in frameworks such as NIST SP 800-92 and ISO 27001 standards for information security management.