Full Report
Secure boot is an important part of ensuring that a running device is not modified. While reading a reference manual for the NNXP i.MX 6/7/8M Application Processors (AP) , they noticed a weird quote that "The DCD based SoC initialization mechanism should not be used once the boot process exits the ROM". In the UBoot Github report, this change had been added but reverted later - this is the beginning of the research. This chip is provides High Assurance Boot (HAB) functionality to protect the integrity and authenticity of the first boot loader stage retrieved from non-volatile storage. The HAB exports several API functions that allow further boot stages for ROM-based authentication. For information on how several commands are executed, Device Configuration Data (DCD) and Command Sequence File File (CSF). These sections perform device configuration and image authentication. However, there is a vulnerability: the DCD and CSF sections validation occurs after some use. As a result, this allows for the reading, polling and writing to configuration register spaces prior to authenticating them. What result does this have on the system? An attacker can use the unverified DCD section to modify further stages in the boot process. For instance, U-Boot's authenticate_image function can be patched to always succeed. It appears they can even modify the currently loaded boot step to hijack control flow entirely. The major issue is that the DCD Execution allows for execution outside of the ROM Context. The DCD code is attempts to sandbox specific regions but it just wasn't enough. This same vulnerability existed in the CSF functionality as well but the usage of deprecated functions being called. The author concludes with why the study of old vulnerabilities is important. This design issue, of allowing ROM-resident code to be shared between boot stages, gave us an potential access problem. Overall, this was a solid post on the secure boot process and design level vulnerability discovery.
Analysis Summary
Based on the provided context regarding the vulnerability research, here is the summarized report. Please note that specific CVE IDs, CVSS scores, and confirmed patch versions were *not* present in the source text, so placeholders are used where necessary according to specialized vulnerability reporting standards.
# Vulnerability: Premature DCD/CSF Execution Allows Secure Boot Bypass on NXP i.MX Processors
## CVE Details
- CVE ID: [To be assigned or inferred based on final report]
- CVSS Score: [Not specified in context - Likely High due to Secure Boot Bypass] (Severity: [High/Critical])
- CWE: CWE-269: Improper Privilege Management / CWE-754: Improper Control of Generation of Code ('Code Injection')
## Affected Systems
- Products: NXP i.MX 6/7/8M Application Processors (AP) implementing High Assurance Boot (HAB).
- Versions: Systems utilizing the ROM-based bootloader that executes Device Configuration Data (DCD) and Command Sequence File (CSF) mechanisms. (Specific U-Boot interactions were mentioned in research, implying affected firmware environments.)
- Configurations: Any configuration relying on HAB functionality to authenticate boot stages without immediate validation of DCD/CSF content.
## Vulnerability Description
The NXP i.MX processors use High Assurance Boot (HAB) with mechanisms like DCD (Device Configuration Data) and CSF (Command Sequence File) for device setup and image authentication during the initial boot process performed by ROM code.
The vulnerability lies in the **timing of validation**. The DCD and CSF sections are processed and executed *before* their integrity and authenticity checks are fully complete. Specifically, the DCD execution allows for configuration register reads, polling, and writes to occur outside the intended ROM context and prior to authentication.
This flaw allows an attacker to leverage the *unverified* DCD section to modify subsequent boot stages. For example, critical functions like U-Boot's `authenticate_image` or control flow mechanisms of the currently loaded boot step can be hijacked or redirected by modifying configuration registers or memory structures before the system verifies its own chain of trust. A similar timing issue existed for CSF functionality due to reliance on deprecated functions.
## Exploitation
- Status: Proof-of-Concept (PoC) development implied through description of control flow hijacking (e.g., patching `authenticate_image` to always succeed). (Not explicitly stated as exploited in the wild.)
- Complexity: Medium to High (Requires deep knowledge of the boot ROM, DCD structure, and target processor architecture.)
- Attack Vector: Local (Requires ability to influence the initial storage contents read by the ROM loader).
## Impact
- Confidentiality: High (Successful hijacking of later boot stages could bypass encryption or security mechanisms.)
- Integrity: Critical (Attacker gains control over the boot execution flow and can inject malicious code or configuration changes, resulting in persistent compromise.)
- Availability: High (System could be bricked or placed into an unusable state by malicious configuration.)
## Remediation
### Patches
- [Vendor-specific patches from NXP or updates to affected bootloaders (e.g., U-Boot) are required to enforce DCD/CSF validation *before* execution/configuration is permitted.]
- [Specific version numbers are unavailable from the source text.]
### Workarounds
- Disabling or strictly controlling the use of DCD initialization sequences if possible in the manufacturing or deployment environment.
- Ensuring that the DCD/CSF content adheres to the strict security requirements imposed by the final validated routines, though this is difficult given the vulnerability timing.
## Detection
- Indicators of compromise would likely manifest as unusual register states in hardware or memory corruption occurring very early in the boot process, prior to OS loading.
- Detection methods should focus on monitoring memory access and register modifications during the initial boot sequence phase, specifically looking for writes outside the established ROM configuration area before the standard authentication handshake is complete. Tools capable of monitoring hardware initialization sequences would be required.
## References
- Vendor Advisory (NXP): [Not specified]
- Research Source (U-Boot discussions): Mentioned in UBoot Github report (details not provided).
- Primary Research Link: [The context is derived from a descriptive article, no direct link provided to the findings itself.]