CVE-2017-3225 in Das U-Boot
Summary
by MITRE
Das U-Boot is a device bootloader that can read its configuration from an AES encrypted file. For devices utilizing this environment encryption mode, U-Boot's use of a zero initialization vector may allow attacks against the underlying cryptographic implementation and allow an attacker to decrypt the data. Das U-Boot's AES-CBC encryption feature uses a zero (0) initialization vector. This allows an attacker to perform dictionary attacks on encrypted data produced by Das U-Boot to learn information about the encrypted data.
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Analysis
by VulDB Data Team • 12/28/2024
The vulnerability identified as CVE-2017-3225 affects Das U-Boot, a widely used open-source bootloader implementation that serves as the first program executed on embedded devices during the boot process. This bootloader is critical for device initialization and firmware loading, making it a prime target for attackers seeking persistent access to embedded systems. The vulnerability specifically resides in U-Boot's implementation of AES-CBC encryption for storing device configurations, a feature designed to protect sensitive boot parameters from unauthorized access. When devices employ this encryption mode, the bootloader stores configuration data in an AES-encrypted file, which should theoretically provide security against tampering and information disclosure. However, the implementation contains a fundamental flaw that undermines the cryptographic protection mechanism through improper initialization vector handling.
The technical flaw in CVE-2017-3225 stems from U-Boot's use of a zero initialization vector (IV) when implementing AES-CBC encryption for configuration data. In cryptographic terms, the initialization vector serves as a randomization parameter that ensures identical plaintext blocks produce different ciphertext blocks during encryption. When a zero IV is used consistently, it creates predictable patterns in the encrypted data that can be exploited by attackers. This specific implementation violates security best practices outlined in industry standards such as NIST SP 800-38A for block cipher modes of operation. The zero IV usage creates a deterministic encryption scenario where attackers can perform dictionary attacks and pattern analysis against the encrypted configuration data, effectively breaking the confidentiality guarantees that AES-CBC is designed to provide.
The operational impact of this vulnerability extends beyond simple information disclosure, as it provides attackers with a pathway to understand and potentially manipulate device configurations. Attackers can leverage the predictable encryption patterns to reconstruct portions of the encrypted configuration data, potentially gaining insights into device settings, network configurations, or even authentication parameters stored in the encrypted environment. This vulnerability affects devices that rely on U-Boot's environment encryption feature, which is commonly implemented in embedded systems, IoT devices, and network equipment where boot-time configuration security is critical. The attack vector is particularly concerning because it operates at the bootloader level, meaning it can potentially allow attackers to gain persistent access to devices before operating systems are fully loaded, enabling more sophisticated attack scenarios. This vulnerability aligns with ATT&CK technique T1542.001 for bootkit creation and represents a significant weakness in the device's security posture that could lead to complete system compromise.
The exploitation of this vulnerability can be categorized under CWE-327, which addresses the use of insecure cryptographic algorithms or modes of operation, specifically highlighting the weakness in the initialization vector implementation. The vulnerability demonstrates a failure to implement proper cryptographic practices that are fundamental to secure system design, creating a situation where the encryption mechanism becomes a point of weakness rather than a security enhancement. Organizations should implement immediate mitigations including updating to U-Boot versions that properly implement random initialization vectors for AES-CBC encryption, disabling environment encryption if not strictly required, or implementing additional security controls at the network level to detect and prevent exploitation attempts. The vulnerability also underscores the importance of cryptographic implementation review processes and adherence to established security standards, as the issue could have been prevented through proper security testing and code review procedures that would have identified the insecure IV usage pattern during development.