CVE-2018-1000205 in U-Boot
Summary
by MITRE
U-Boot contains a CWE-20: Improper Input Validation vulnerability in Verified boot signature validation that can result in Bypass verified boot. This attack appear to be exploitable via Specially crafted FIT image and special device memory functionality.
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Analysis
by VulDB Data Team • 02/22/2020
The vulnerability identified as CVE-2018-1000205 resides within U-Boot, a widely used open-source bootloader that serves as the foundation for numerous embedded systems and embedded devices across various industries. This weakness manifests as a CWE-20: Improper Input Validation flaw specifically within the Verified boot signature validation mechanism, representing a critical security gap that undermines the integrity protection mechanisms designed to safeguard device boot processes. The vulnerability's exploitation potential becomes particularly concerning when considering that it can be triggered through carefully crafted Flexible Image Tree (FIT) images combined with specific device memory functionalities, creating a pathway for adversaries to bypass critical boot-time security controls.
The technical implementation of this vulnerability stems from insufficient validation of input parameters during the signature verification process within U-Boot's verified boot framework. When a device attempts to boot using a FIT image, the bootloader performs cryptographic signature checks to ensure the image's authenticity and integrity. However, the improper input validation allows malicious actors to construct FIT images that contain malformed or specially crafted signatures that pass the verification checks despite being invalid. This flaw directly violates the fundamental security principle of cryptographic validation, where all inputs should be rigorously checked against expected formats and values before being accepted as legitimate. The vulnerability's exploitation requires specific conditions involving device memory handling capabilities, suggesting that it may be device-specific or require certain hardware configurations to be effectively leveraged.
The operational impact of this vulnerability extends far beyond simple bypass scenarios, as it fundamentally compromises the security posture of devices relying on U-Boot for their boot process. When verified boot is successfully bypassed, adversaries gain the ability to load unauthorized code into the device's memory, potentially leading to complete system compromise and persistent backdoor access. This vulnerability affects embedded systems across multiple sectors including industrial control systems, networking equipment, automotive systems, and IoT devices where U-Boot serves as the primary bootloader. The implications are particularly severe given that many of these systems operate in environments where physical access is limited or controlled, making remote exploitation more challenging but not impossible through carefully crafted attack vectors. The vulnerability aligns with ATT&CK technique T1068, which describes the use of local system exploitation to gain elevated privileges, and represents a critical failure in the boot integrity chain that can enable subsequent attacks.
Mitigation strategies for this vulnerability must address both the immediate security gap and broader system architecture considerations. Device manufacturers should implement immediate firmware updates containing patches that correct the input validation logic within U-Boot's signature verification process. The fix typically involves strengthening the validation routines to properly check all input parameters and reject malformed or unexpected signature formats. Additionally, organizations should consider implementing additional security controls such as secure boot enforcement mechanisms, hardware security modules, and regular firmware integrity checks. The vulnerability demonstrates the importance of robust input validation as outlined in CWE-20 and aligns with security best practices from NIST SP 800-145 and ISO/IEC 27031 standards. Long-term mitigation includes adopting more sophisticated boot integrity verification approaches and ensuring that security reviews are conducted throughout the development lifecycle rather than as afterthoughts. Organizations should also maintain comprehensive inventory systems of all devices using U-Boot to facilitate rapid response to similar vulnerabilities and implement proper security monitoring to detect unauthorized boot process modifications.