CVE-2013-4577 in GRUB
Summary
by MITRE
A certain Debian patch for GNU GRUB uses world-readable permissions for grub.cfg, which allows local users to obtain password hashes, as demonstrated by reading the password_pbkdf2 directive in the file.
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Analysis
by VulDB Data Team • 03/17/2019
The vulnerability identified as CVE-2013-4577 represents a critical security flaw in the GNU GRUB bootloader implementation within Debian systems. This issue stems from an improper permission configuration where the grub.cfg configuration file is created with world-readable permissions, specifically allowing any local user to access sensitive authentication information stored within the bootloader configuration. The vulnerability is particularly concerning because it directly exposes password hash information that should remain protected from unauthorized access. The grub.cfg file contains the password_pbkdf2 directive which stores password hashes in a format that can be easily extracted and potentially cracked by malicious actors. This flaw demonstrates a fundamental failure in privilege separation and access control mechanisms within the bootloader configuration process. The security implications extend beyond simple information disclosure as the exposed password hashes provide attackers with direct access to authentication credentials that could be used to escalate privileges or gain unauthorized access to systems protected by GRUB authentication.
The technical root cause of this vulnerability lies in the Debian-specific patch implementation for GRUB that incorrectly sets file permissions during the configuration file generation process. When the grub.cfg file is created, it is assigned permissions that permit read access to all users on the system rather than restricting access to only the root user or system administrators. This misconfiguration violates fundamental security principles and creates an attack surface that allows local privilege escalation through credential exposure. The vulnerability specifically affects systems where GRUB has been patched according to Debian's security guidelines but where the file permissions have not been properly enforced. This issue is classified under CWE-732 as an Incorrect Permission Assignment for Critical Resource, which represents a critical weakness in access control mechanisms. The flaw enables attackers to directly read sensitive information from the bootloader configuration, bypassing normal authentication mechanisms and potentially providing access to systems that should be protected by password-protected boot processes.
The operational impact of CVE-2013-4577 extends significantly beyond the immediate exposure of password hashes, as it fundamentally undermines the security posture of affected systems. Local users who can read the grub.cfg file gain access to password hashes that can be used for offline password cracking attacks, potentially leading to full system compromise. The vulnerability creates a persistent security risk that remains active as long as the improperly configured file exists, making it particularly dangerous in multi-user environments where system administrators may not be aware of the exposure. Additionally, this flaw can be exploited as part of broader attack vectors where attackers combine the exposed credentials with other vulnerabilities to achieve unauthorized access to protected systems. The impact is amplified in enterprise environments where multiple systems may be affected by the same Debian patch, creating a potential attack surface that could be leveraged to compromise entire network infrastructures. This vulnerability also violates the principle of least privilege and demonstrates poor security hygiene in the management of critical system components.
Mitigation strategies for CVE-2013-4577 must address both immediate remediation and long-term prevention of similar issues. The primary immediate fix involves correcting the file permissions on grub.cfg to ensure only root access is permitted, typically through setting permissions to 600 or equivalent restrictive access controls. System administrators should also verify that all GRUB configuration files are properly secured and monitor for any unauthorized modifications to bootloader configurations. The broader mitigation approach includes implementing proper security auditing procedures to detect and prevent incorrect permission assignments on critical system files. Organizations should also consider implementing automated security scanning tools that can identify misconfigured files and permissions across their infrastructure. Regular security updates and patch management processes should be enhanced to ensure that security patches are properly applied without introducing new vulnerabilities. This vulnerability highlights the importance of following security best practices in system configuration management and emphasizes the need for comprehensive security testing of system components, particularly those that handle authentication and authorization functions. The remediation process should also include reviewing and updating security policies to prevent similar issues from occurring in other system components and ensuring that access control mechanisms are properly enforced throughout the system lifecycle.