CVE-2018-0021 in Junos
Summary
by MITRE
If all 64 digits of the connectivity association name (CKN) key or all 32 digits of the connectivity association key (CAK) key are not configured, all remaining digits will be auto-configured to 0. Hence, Juniper devices configured with short MacSec keys are at risk to an increased likelihood that an attacker will discover the secret passphrases configured for these keys through dictionary-based and brute-force-based attacks using spoofed packets. Affected releases are Juniper Networks Junos OS: 14.1 versions prior to 14.1R10, 14.1R9; 14.1X53 versions prior to 14.1X53-D47; 15.1 versions prior to 15.1R4-S9, 15.1R6-S6, 15.1R7; 15.1X49 versions prior to 15.1X49-D100; 15.1X53 versions prior to 15.1X53-D59; 16.1 versions prior to 16.1R3-S8, 16.1R4-S8, 16.1R5; 16.2 versions prior to 16.2R1-S6, 16.2R2; 17.1 versions prior to 17.1R2.
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Analysis
by VulDB Data Team • 02/27/2023
The vulnerability described in CVE-2018-0021 represents a critical weakness in Juniper Networks Junos OS implementations of MacSec key management protocols. This flaw specifically affects the configuration handling of connectivity association name (CKN) and connectivity association key (CAK) parameters, which are fundamental components of the IEEE 802.1AE MacSec security framework. When administrators fail to configure the complete 64-digit CKN or 32-digit CAK values, the system automatically pads the remaining positions with zeros, creating predictable and insufficiently random cryptographic keys. This behavior fundamentally undermines the security assumptions underlying MacSec implementations and creates a significant attack surface that directly violates the principles of cryptographic key strength as defined by industry standards.
The technical implementation of this vulnerability stems from inadequate input validation and key generation logic within the Junos OS networking stack. When short keys are provided, the system's automatic zero-padding mechanism creates deterministic patterns that dramatically reduce the effective key space available for cryptographic operations. This flaw aligns with CWE-326 - Inadequate Encryption Strength, as it effectively reduces the entropy of cryptographic keys to a level that makes them vulnerable to systematic attack methodologies. The vulnerability is particularly concerning because it operates at the network infrastructure level, where MacSec is typically deployed to secure Layer 2 communications between network devices, making it a prime target for attackers seeking to compromise network integrity and confidentiality.
The operational impact of this vulnerability extends far beyond simple cryptographic weakness, creating substantial risk for organizations relying on Juniper network equipment for secure communications. Attackers can leverage dictionary-based and brute-force attacks to systematically test potential key combinations, exploiting the predictable zero-padded configurations to recover secret passphrases. This attack vector directly maps to ATT&CK technique T1210 - Exploitation of Remote Services, where adversaries attempt to gain access through weak cryptographic implementations. The vulnerability affects multiple Junos OS versions across several release branches, indicating a systemic issue within the software's key management implementation that required coordinated patching across numerous product lines. Organizations using affected versions face increased risk of unauthorized network access, data interception, and potential lateral movement within their network infrastructure.
Mitigation strategies for CVE-2018-0021 require immediate configuration remediation and comprehensive network security assessment. Network administrators must ensure that all CKN and CAK values are properly configured with complete cryptographic strength, eliminating the automatic zero-padding behavior through explicit configuration of full-length keys. The recommended approach involves implementing strict key management policies that enforce minimum entropy requirements for MacSec key configurations, aligning with NIST SP 800-137 guidelines for cryptographic key management. Organizations should also deploy network monitoring solutions capable of detecting anomalous traffic patterns indicative of brute-force attack attempts against MacSec key spaces. Additionally, the affected Junos OS versions should be upgraded to patched releases as specified in the vulnerability timeline, with particular attention to the specific version requirements listed in the advisory. Regular security audits of network device configurations should be conducted to prevent recurrence of similar issues, ensuring that all cryptographic parameters meet current security standards and that automatic configuration behaviors do not introduce unintended weaknesses into the network infrastructure.