CVE-2017-5933 in NetScaler ADC
Summary
by MITRE
Citrix NetScaler ADC and NetScaler Gateway 10.5 before Build 65.11, 11.0 before Build 69.12/69.123, and 11.1 before Build 51.21 does not properly generate GCM nonces, which makes it easier for remote attackers to obtain the authentication key and spoof data by leveraging a reused nonce in a session and a "forbidden attack," a similar issue to CVE-2016-0270.
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Analysis
by VulDB Data Team • 08/25/2024
The vulnerability identified as CVE-2017-5933 affects Citrix NetScaler ADC and NetScaler Gateway appliances across multiple version branches, specifically targeting the cryptographic implementation of Galois/Counter Mode (GCM) authentication. This weakness stems from improper nonce generation mechanisms that create predictable or reused values during cryptographic operations, fundamentally compromising the security assurances provided by the encryption protocol. The vulnerability is particularly concerning because it enables remote attackers to exploit reused nonces, which directly undermines the core security properties of GCM mode encryption.
The technical flaw manifests in the improper generation of initialization vectors or nonces used in the GCM encryption process, which is a critical component of the Advanced Encryption Standard (AES) with Galois/Counter Mode. According to CWE-327, this represents a weakness in the use of a broken cryptographic algorithm where the nonce reuse creates predictable patterns that can be exploited. The implementation fails to ensure proper uniqueness of nonces for each encryption operation, creating opportunities for attackers to perform what is known as a "forbidden attack" where the reused nonce allows for the extraction of authentication keys and subsequent data spoofing.
The operational impact of this vulnerability extends beyond simple data confidentiality breaches, as it enables sophisticated attacks that can compromise the entire security posture of affected systems. Attackers can leverage the reused nonce to perform key recovery attacks, effectively breaking the encryption and gaining unauthorized access to sensitive data transmitted through the affected NetScaler appliances. This vulnerability directly aligns with ATT&CK technique T1566, which covers credential harvesting through various means including cryptographic weaknesses, and represents a significant risk to organizations relying on these appliances for network security and authentication services.
Mitigation strategies for CVE-2017-5933 require immediate implementation of vendor-provided patches and firmware updates that address the nonce generation algorithms within the Citrix NetScaler appliances. Organizations should also consider implementing additional monitoring and detection measures to identify potential exploitation attempts, particularly focusing on unusual network traffic patterns that might indicate nonce reuse or cryptographic anomalies. The fix typically involves updating the appliance firmware to versions that properly implement nonce generation mechanisms, ensuring each nonce is unique and cryptographically random for every encryption operation. Security teams should also review and validate their current cryptographic configurations to ensure that other similar vulnerabilities are not present in their infrastructure, as this type of weakness often indicates broader cryptographic implementation issues that may require comprehensive security assessments.