CVE-2015-0949 in BIOS
Summary
by MITRE
The System Management Mode (SMM) implementation in Dell Latitude E6430 BIOS Revision A09, HP EliteBook 850 G1 BIOS revision L71 Ver. 01.09, and possibly other BIOS implementations does not ensure that function calls operate on SMRAM memory locations, which allows local users to bypass the Secure Boot protection mechanism and gain privileges by leveraging write access to physical memory.
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Analysis
by VulDB Data Team • 04/16/2022
The vulnerability identified as CVE-2015-0949 represents a critical flaw in the System Management Mode implementation within specific BIOS firmware versions of enterprise laptops from Dell and HP. This issue resides in the fundamental security architecture of modern computing systems where the System Management Mode serves as a privileged execution environment designed to handle critical system functions while maintaining isolation from the operating system. The vulnerability specifically affects Dell Latitude E6430 BIOS Revision A09 and HP EliteBook 850 G1 BIOS revision L71 Ver. 01.09, though similar implementations across other manufacturers may be susceptible to the same weakness.
The technical flaw stems from improper memory management within the SMM implementation where function calls do not adequately validate that they operate exclusively on SMRAM (System Management Random Access Memory) locations. SMRAM represents a protected memory region that should be isolated from normal operating system processes and maintain strict access controls to prevent unauthorized modifications. When the SMM implementation fails to enforce this memory boundary enforcement, it creates a pathway for malicious actors to manipulate system functions through direct physical memory access. This weakness directly violates the principle of least privilege and memory isolation that forms the foundation of secure system architecture.
The operational impact of this vulnerability extends far beyond simple privilege escalation, as it fundamentally undermines the Secure Boot protection mechanism that modern systems rely upon to prevent unauthorized code execution during the boot process. Local users with write access to physical memory can exploit this flaw to bypass critical security measures that are supposed to ensure only trusted code executes during system initialization. This capability allows attackers to load malicious firmware components or modify existing system functions, potentially leading to complete system compromise and persistent backdoor access. The vulnerability's exploitation requires physical access to the target system, but once achieved, it provides attackers with unprecedented control over system operations and can persist across reboots.
This vulnerability aligns with CWE-254 and CWE-119 categories, representing weaknesses in security mechanisms and memory safety issues respectively. From an ATT&CK framework perspective, this flaw maps to techniques involving privilege escalation and persistence mechanisms, specifically leveraging system firmware as a vector for maintaining long-term access. The vulnerability demonstrates the critical importance of firmware security and highlights how weaknesses in low-level system components can create pathways for sophisticated attacks that bypass traditional operating system security controls. Organizations should implement comprehensive firmware update policies, physical security measures, and continuous monitoring of system integrity to mitigate risks associated with such low-level vulnerabilities.
The remediation approach for CVE-2015-0949 requires immediate firmware updates from affected vendors, though the underlying architectural issue suggests that similar vulnerabilities may exist in other implementations. System administrators should also consider implementing physical security controls to prevent unauthorized access to target systems and deploy memory integrity monitoring solutions that can detect unauthorized modifications to protected memory regions. The vulnerability serves as a reminder of the critical need for supply chain security and the importance of validating firmware integrity throughout the entire system lifecycle.