CVE-2017-17382 in Netscaler Application Delivery Controller
Summary
by MITRE
Citrix NetScaler Application Delivery Controller (ADC) and NetScaler Gateway 10.5 before build 67.13, 11.0 before build 71.22, 11.1 before build 56.19, and 12.0 before build 53.22 might allow remote attackers to decrypt TLS ciphertext data by leveraging a Bleichenbacher RSA padding oracle, aka a ROBOT attack.
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Analysis
by VulDB Data Team • 12/25/2024
The vulnerability identified as CVE-2017-17382 affects Citrix NetScaler Application Delivery Controller and NetScaler Gateway appliances across multiple versions including 10.5, 11.0, 11.1, and 12.0. This security flaw represents a critical weakness in the cryptographic implementation that enables remote attackers to exploit a known vulnerability in RSA padding schemes. The issue stems from the appliance's failure to properly validate RSA padding during TLS handshake processes, creating a pathway for attackers to perform cryptographic attacks that compromise encrypted communications.
The technical root cause of this vulnerability lies in the implementation of RSA decryption operations within the Citrix NetScaler appliances. When the system processes RSA encrypted data during TLS connections, it inadvertently reveals information about the validity of padding through timing variations or error responses. This behavior creates a padding oracle scenario that allows attackers to iteratively test different padding values and determine the correct padding through statistical analysis and pattern recognition. The vulnerability specifically relates to the Bleichenbacher attack vector, which exploits the way RSA signatures are verified and how padding validation errors are handled during the decryption process.
This vulnerability impacts the fundamental security guarantees of TLS encryption by allowing attackers to decrypt sensitive data transmitted through affected NetScaler appliances. The attack can be executed remotely without requiring authentication, making it particularly dangerous for organizations that rely on these appliances for secure network communications. The implications extend beyond simple data theft to potentially enable man-in-the-middle attacks, session hijacking, and the compromise of confidential business communications, user credentials, and sensitive corporate data. Organizations using these vulnerable versions face significant risk of data breaches and regulatory compliance violations due to the exposure of encrypted communications.
The operational impact of this vulnerability requires immediate attention from security teams responsible for Citrix appliance management. Affected organizations must prioritize patching their NetScaler appliances to the latest supported builds that contain the necessary cryptographic fixes. The mitigation strategy involves updating to versions that properly implement constant-time padding validation and eliminate the oracle behavior that enables the attack. Security monitoring should be enhanced to detect potential exploitation attempts, and network segmentation should be implemented to limit the attack surface. Additionally, organizations should conduct comprehensive vulnerability assessments to identify all instances of affected appliances and implement proper cryptographic key management practices to minimize the impact of potential exploitation.
This vulnerability aligns with CWE-310, which addresses cryptographic weaknesses in padding validation mechanisms, and maps to ATT&CK technique T1566 for initial access through credential harvesting and T1041 for data exfiltration. The attack vector demonstrates the importance of proper cryptographic implementation and the dangers of oracle-based attacks in network security systems. Organizations should review their cryptographic implementations against industry standards and ensure that all TLS implementations follow best practices for padding validation and error handling to prevent similar vulnerabilities from being exploited in the future.