CVE-2018-6441 in Fabric OS
Summary
by MITRE
A vulnerability in Secure Shell implementation of Brocade Fabric OS versions before 8.2.1, 8.1.2f, 8.0.2f, 7.4.2d could allow a local attacker to provide arbitrary environment variables, and bypass the restricted configuration shell.
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Analysis
by VulDB Data Team • 04/11/2020
The vulnerability identified as CVE-2018-6441 represents a critical security flaw within the Secure Shell implementation of Brocade Fabric OS software across multiple version branches. This issue affects versions prior to 8.2.1, 8.1.2f, 8.0.2f, and 7.4.2d, creating a significant risk for network infrastructure administrators who rely on Brocade switches for their storage area network operations. The vulnerability specifically targets the restricted configuration shell mechanism that is designed to limit administrative access and prevent unauthorized system modifications. This flaw allows a local attacker with access to the system to manipulate environment variables in a manner that circumvents the intended security controls.
The technical implementation of this vulnerability stems from insufficient validation of environment variables within the SSH daemon's execution context. When users establish Secure Shell connections to Brocade switches, the system initializes certain environment variables that should be restricted to prevent escalation of privileges. However, the flawed implementation fails to properly sanitize or validate these variables, allowing an attacker to inject malicious values that can alter the execution environment. This particular weakness aligns with CWE-74, which describes improper neutralization of special elements in output used by a downstream component, and CWE-22, which addresses path traversal vulnerabilities that can occur when input is not properly validated. The vulnerability operates at the system level where the SSH daemon processes user sessions, making it particularly dangerous as it can be exploited from within the local system boundaries.
The operational impact of CVE-2018-6441 extends far beyond simple privilege escalation, as it fundamentally undermines the security model of the restricted configuration shell. An attacker who successfully exploits this vulnerability can bypass the intended limitations of the restricted shell environment, potentially gaining access to sensitive system functions, configuration files, and network management capabilities. This exploitation capability directly relates to ATT&CK technique T1068, which covers 'Exploitation for Privilege Escalation', and T1566, which addresses 'Phishing for Information'. The vulnerability essentially allows an attacker to transform a controlled restricted shell session into a fully privileged administrative session, which could lead to complete network compromise, data exfiltration, or disruption of critical storage infrastructure services. Organizations using affected Brocade Fabric OS versions face significant risk of unauthorized access to their SAN environments, potentially affecting thousands of connected storage devices and systems.
Mitigation strategies for CVE-2018-6441 require immediate action to upgrade affected Brocade Fabric OS installations to versions 8.2.1, 8.1.2f, 8.0.2f, or 7.4.2d, respectively, depending on the current version in use. Network administrators should implement comprehensive patch management procedures to ensure all affected switches are updated across the enterprise infrastructure. Additional defensive measures include implementing strict access controls, monitoring SSH session logs for suspicious environment variable modifications, and conducting regular security assessments of network management interfaces. The vulnerability demonstrates the importance of proper input validation and environment variable handling in privileged execution contexts, as recommended by security frameworks such as the OWASP Top Ten and NIST Special Publication 800-125. Organizations should also consider implementing network segmentation and privilege separation techniques to limit the potential impact of such vulnerabilities, ensuring that even if one system is compromised, the attacker cannot easily move laterally through the network infrastructure.