# CS35L27 Firmware Security Analysis

## Overview

This repository contains supporting materials and analysis for a hardware and firmware security review of the Cirrus Logic CS35L27 audio codec as deployed in the iPhone 14 Pro Max running iOS 26.2. The work identifies firmware behaviors **consistent with potential covert channel functionality** and documents extended command handlers, state machine routines, GPIO/I2S usage patterns, and statistical anomalies within the production firmware.

## Repository Structure

- **CS35L27_iPhone14ProMax_PSIRT_Main_Report.md**  
  Full disclosure report suitable for PSIRT/CERT submission, including risk impact and technical assessment.
- **Appendix_A_disassembly.txt**  
  Key disassembly excerpts of extended command handlers and buffer logic.
- **Appendix_B_statistical_summary.csv**  
  Statistical summaries covering register usage, command frequency, and pattern analysis.
- **Appendix_C_firmware_sequences.txt**  
  Representative event sequences and state-machine evidence observed in the firmware.
- **Appendix_D_methodology.txt**  
  Methods, analysis environment, and extraction limitations.

## Key Findings

- **Bidirectional Audio Capability:**  
  Over 33% of configuration states enable input or microphone sampling modes within the CS35L27 firmware.
- **Extended Handler Exposure:**  
  Production firmware implements command handlers (e.g., 0xC7 and 0x81) that permit privileged reconfiguration.
- **Behavior Consistent with Potential Covert Channel:**  
  State machine routines and GPIO/I2S toggling patterns could enable unauthorized audio or data paths.
- **Elevated Statistical Likelihood:**  
  Pattern analysis suggests purposeful or exploitable logic beyond normal diagnostic or test activity.

## Intended Audience

- Product Security Incident Response Teams (PSIRT)
- Firmware and hardware security researchers
- Auditors of embedded device supply chains

## Caveats

- All analysis performed on a production iPhone 14 Pro Max (iOS 26.2), single unit, without a reference/control device.
- Attribution of firmware behaviors is based on static/code and statistical analysis.
- No userland exploit or attack code is included—this research focuses on firmware and hardware level risk.