CVE-2015-3642 in Netscaler Application Delivery Controller
Summary
by MITRE
The TLS and DTLS processing functionality in Citrix NetScaler Application Delivery Controller (ADC) and NetScaler Gateway devices with firmware 9.x before 9.3 Build 68.5, 10.0 through Build 78.6, 10.1 before Build 130.13, 10.1.e before Build 130.1302.e, 10.5 before Build 55.8, and 10.5.e before Build 55.8007.e makes it easier for man-in-the-middle attackers to obtain cleartext data via a padding-oracle attack, a variant of CVE-2014-3566 (aka POODLE).
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Analysis
by VulDB Data Team • 11/03/2019
The vulnerability identified as CVE-2015-3642 represents a critical security flaw in Citrix NetScaler ADC and Gateway devices that affects multiple firmware versions across different release streams. This weakness specifically targets the Transport Layer Security and Datagram Transport Layer Security protocols implementation, creating a significant pathway for attackers to compromise encrypted communications. The vulnerability stems from improper handling of padding in cryptographic operations, making it susceptible to padding-oracle attacks that exploit weaknesses in the protocol processing mechanisms. The issue is particularly concerning as it enables man-in-the-middle attackers to decrypt previously encrypted data and potentially access sensitive information transmitted through these network devices, effectively undermining the core security assurances provided by TLS and DTLS encryption protocols.
The technical implementation flaw manifests in the way Citrix NetScaler devices process TLS and DTLS handshakes and data encryption operations. When these devices encounter encrypted data packets, they fail to properly validate padding structures during decryption processes, creating an oracle that attackers can exploit to gradually reveal the plaintext content. This vulnerability specifically relates to the implementation of the SSL/TLS protocol stack where the padding validation mechanism is insufficiently robust against oracle-based attacks. The flaw allows attackers to send specially crafted packets and observe the device's response to determine valid padding structures, ultimately enabling them to reconstruct the original cleartext data without possessing the encryption keys. This type of vulnerability is categorized under CWE-310 as "Cryptographic Issues" and more specifically relates to CWE-312 for "Sensitive Data Exposure" and CWE-209 for "Information Exposure Through an Error Message" which demonstrates how the device's error handling contributes to the vulnerability.
The operational impact of this vulnerability extends beyond simple data exposure, as it fundamentally compromises the integrity of encrypted communications within enterprise networks that rely on Citrix NetScaler appliances for secure data transmission. Organizations using affected NetScaler devices face significant risks including potential data breaches, unauthorized access to confidential information, and violations of compliance requirements such as PCI DSS, HIPAA, and other regulatory frameworks that mandate secure communication channels. The vulnerability's susceptibility to man-in-the-middle attacks means that attackers can intercept and modify data in transit without detection, potentially leading to financial losses, intellectual property theft, and reputational damage. Network administrators must consider that this vulnerability affects not only direct communications but also any services that depend on the NetScaler's secure tunneling capabilities, including remote access solutions, load balancing services, and SSL offloading functions that are critical to enterprise infrastructure security.
Organizations affected by CVE-2015-3642 should immediately implement mitigations including firmware upgrades to the latest available versions that address the padding-oracle vulnerability, along with network segmentation and monitoring to detect potential exploitation attempts. The implementation of proper key management practices, including regular rotation of encryption keys and implementation of secure key storage mechanisms, should complement these technical fixes. Security teams should also consider deploying network intrusion detection systems capable of identifying anomalous traffic patterns that may indicate padding-oracle attack attempts, as well as implementing additional authentication mechanisms beyond simple TLS/DTLS to provide defense-in-depth. The vulnerability demonstrates the importance of maintaining up-to-date security patches and conducting regular vulnerability assessments, particularly for critical infrastructure components that handle sensitive data. From an ATT&CK framework perspective, this vulnerability maps to T1071.001 for Application Layer Protocol and T1566 for Phishing, as attackers may leverage the compromised communications to establish further footholds within networks, making comprehensive network security monitoring essential for early detection and response.