CVE-2015-5281 in Red Hat
Summary
by MITRE
The grub2 package before 2.02-0.29 in Red Hat Enterprise Linux (RHEL) 7, when used on UEFI systems, allows local users to bypass intended Secure Boot restrictions and execute non-verified code via a crafted (1) multiboot or (2) multiboot2 module in the configuration file or physically proximate attackers to bypass intended Secure Boot restrictions and execute non-verified code via the (3) boot menu.
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Analysis
by VulDB Data Team • 11/23/2024
The vulnerability identified as CVE-2015-5281 represents a critical flaw in the grub2 bootloader implementation within Red Hat Enterprise Linux 7 systems utilizing UEFI firmware. This security weakness specifically targets the Secure Boot mechanisms that are fundamental to modern system integrity protection, creating pathways for unauthorized code execution that bypass essential security controls. The vulnerability affects systems where grub2 serves as the primary bootloader, particularly in enterprise environments where UEFI-based systems are prevalent. The flaw stems from insufficient validation mechanisms within the bootloader's handling of multiboot and multiboot2 module specifications, which are standard protocols for loading operating system kernels and additional modules in UEFI environments. Attackers can exploit this vulnerability through multiple vectors including configuration file manipulation and physical proximity attacks, making it particularly concerning for enterprise security postures.
The technical implementation of this vulnerability resides in the grub2 bootloader's failure to properly validate module loading sequences when operating within UEFI environments. Specifically, when the bootloader processes multiboot or multiboot2 module specifications, it does not adequately verify the authenticity and integrity of these modules before execution. This validation gap allows malicious actors to craft specially formatted modules that can bypass the Secure Boot chain of trust. The vulnerability manifests when grub2 processes configuration files containing malicious module references or when attackers interact directly with the boot menu interface. The underlying issue is rooted in the bootloader's insufficient cryptographic verification of module signatures, which should normally be enforced by UEFI firmware but are being circumvented through the grub2 implementation flaw. This represents a direct violation of the security model that Secure Boot is designed to enforce, creating a persistent backdoor for unauthorized code execution.
The operational impact of CVE-2015-5281 extends beyond simple privilege escalation to represent a fundamental compromise of system integrity and trust. Organizations running affected RHEL 7 systems face potential full system compromise where attackers can execute arbitrary code with kernel-level privileges, effectively neutralizing the security protections that Secure Boot is meant to provide. This vulnerability particularly affects enterprise environments where UEFI-based systems are standard, creating widespread exposure across multiple deployment scenarios. The physical proximity attack vector adds another dimension of risk as it allows attackers with access to the system to bypass security measures without requiring network access or complex exploitation techniques. The vulnerability's impact is amplified because it affects the foundational boot process, meaning that any security measures implemented at higher levels of the operating system become ineffective once the bootloader is compromised. This creates a persistent threat that can survive system reboots and is particularly difficult to detect through traditional runtime security monitoring.
Mitigation strategies for CVE-2015-5281 require immediate attention and multiple layers of defensive measures to address the various attack vectors. System administrators should prioritize updating to grub2 versions 2.02-0.29 or later, which contain the necessary patches to properly validate module loading sequences. Additionally, implementing proper access controls and physical security measures can help mitigate the physical proximity attack vector. Organizations should also consider disabling unnecessary boot menu options and implementing strict configuration file access controls to prevent unauthorized modification of bootloader settings. The vulnerability aligns with CWE-264, which addresses permissions, privileges, and access control issues in software implementations, and maps to ATT&CK technique T1068, which covers local privilege escalation through boot or logon initiation. Regular security auditing of bootloader configurations and implementing automated monitoring for unauthorized changes to boot parameters can help detect exploitation attempts. Organizations should also consider implementing additional security controls such as measured boot implementations and hardware-based security features that provide additional layers of protection beyond the vulnerable grub2 implementation.
The broader implications of this vulnerability highlight the critical importance of bootloader security in modern computing environments. As enterprises increasingly rely on UEFI-based systems and Secure Boot mechanisms for protection, vulnerabilities in foundational components like grub2 create cascading security risks that can undermine entire security architectures. This vulnerability demonstrates that even seemingly minor implementation flaws in core system components can result in significant security compromises, emphasizing the need for rigorous security testing and validation of bootloader implementations. The attack vectors identified in CVE-2015-5281 underscore the importance of considering both logical and physical attack surfaces when designing security controls, as the vulnerability can be exploited through configuration file manipulation or direct physical access. Organizations must maintain continuous vigilance regarding bootloader security and ensure that updates are deployed promptly to address known vulnerabilities that could compromise system integrity and trust.