What it does. 'Performs firmware image extraction and analysis using binwalk to identify Part of mukul975/Anthropic-Cybersecurity-Skills (817 security skills) (mukul975/Anthropic-Cybersecurity-Skills).

Install

• npx skills add mukul975/Anthropic-Cybersecurity-Skills --skill performing-firmware-extraction-with-binwalk, or copy the skill folder into ~/.claude/skills/performing-firmware-extraction-with-binwalk/.
• Raw file: curl -sL https://raw.githubusercontent.com/mukul975/Anthropic-Cybersecurity-Skills/HEAD/skills/performing-firmware-extraction-with-binwalk/SKILL.md

SKILL.md (verbatim)

name: performing-firmware-extraction-with-binwalk
description: 'Performs firmware image extraction and analysis using binwalk to identify
  embedded filesystems, compressed archives, bootloaders, kernel images, and cryptographic
  material. Covers entropy analysis for detecting encrypted or compressed regions,
  recursive extraction of nested archives, SquashFS/CramFS/JFFS2 filesystem mounting,
  and string analysis for credential and configuration discovery. Activates for requests
  involving firmware reverse engineering, IoT device analysis, embedded system security
  assessment, or router/camera firmware extraction.

  '
domain: cybersecurity
subdomain: firmware-analysis
tags:
- firmware
- binwalk
- extraction
- entropy
- IoT-security
- reverse-engineering
version: 1.0.0
author: mukul975
license: Apache-2.0
nist_csf:
- ID.RA-01
- PR.PS-01
- DE.AE-02
mitre_attack:
- T1078
- T1190
- T1059
- T1003
- T1110
mitre_f3:
  version: '1.1'
  tactics:
  - reconnaissance
  - initial-access
  techniques:
  - id: T1555
    name: Credentials from Password Stores
    tactic: reconnaissance
    source: attack
  - id: F1029
    name: Gather Customer Information
    tactic: reconnaissance
    source: f3
  - id: T1110.001
    name: 'Brute Force: Password Guessing'
    tactic: initial-access
    source: attack
  - id: F1006.001
    name: 'Account Takeover: Exposed API Key'
    tactic: initial-access
    source: f3
  - id: F1006.002
    name: 'Account Takeover: Exposed Login Credential'
    tactic: initial-access
    source: f3

Performing Firmware Extraction with Binwalk

When to Use

• Analyzing IoT device firmware downloaded from vendor sites or extracted from flash chips
• Reverse engineering router, camera, or embedded device firmware for vulnerability research
• Identifying embedded filesystems (SquashFS, CramFS, JFFS2, UBIFS) within firmware blobs
• Detecting encrypted or compressed regions using entropy analysis
• Extracting hardcoded credentials, API keys, certificates, or configuration files from firmware
• Performing security assessments of embedded devices in authorized penetration tests

Do not use for analyzing standard desktop application binaries or malware samples that are not firmware images; use dedicated malware analysis tools instead.

Prerequisites

• binwalk v3.x installed (pip install binwalk3 or from system package manager)
• Python 3.8+ with standard libraries (struct, math, hashlib, subprocess)
• SquashFS tools (unsquashfs) for mounting extracted SquashFS filesystems
• Jefferson for JFFS2 filesystem extraction (pip install jefferson)
• Sasquatch for non-standard SquashFS variants used by vendors like TP-Link and D-Link
• strings utility (GNU binutils) for string extraction
• Optional: firmware-mod-kit for repacking modified firmware images

Workflow

Step 1: Initial Firmware Reconnaissance

Perform a signature scan to identify embedded file types and their offsets:

# Basic signature scan - identify all recognized file types
binwalk firmware.bin

# Scan with verbose output showing confidence levels
binwalk -v firmware.bin

# Scan for specific file types only
binwalk -y "squashfs" firmware.bin
binwalk -y "gzip\|lzma\|xz" firmware.bin

# Opcode scan to identify CPU architecture
binwalk -A firmware.bin

# Scan for raw strings to find version info, URLs, credentials
binwalk -R "password" firmware.bin
binwalk -R "http://" firmware.bin

Step 2: Entropy Analysis

Analyze entropy to identify encrypted, compressed, and plaintext regions:

# Generate entropy plot
binwalk -E firmware.bin

# Entropy with specific block size for higher resolution
binwalk -E -K 256 firmware.bin

# Combined entropy and signature scan
binwalk -BE firmware.bin

Interpreting entropy values:

• 0.0 - 1.0: Empty or padding regions (null bytes, 0xFF fill)
• 1.0 - 5.0: Plaintext data, code, ASCII strings, configuration
• 5.0 - 7.0: Compressed data (gzip, LZMA, zlib)
• 7.0 - 7.99: Strongly compressed or encrypted data
• ~8.0: Maximum entropy, likely encrypted or random data

Step 3: Extract Embedded Files

Extract all identified components from the firmware image:

# Automatic extraction of known file types
binwalk -e firmware.bin

# Recursive extraction (matryoshka mode) for nested archives
binwalk -Me firmware.bin

# Recursive extraction with depth limit
binwalk -Me -d 5 firmware.bin

# Extract specific file type with custom handler
binwalk -D "squashfs filesystem:squashfs:unsquashfs %e" firmware.bin

# Manual extraction of data at a known offset
dd if=firmware.bin of=extracted.squashfs bs=1 skip=327680 count=4194304

Step 4: Mount and Inspect Extracted Filesystems

Mount extracted filesystems for deep inspection:

# Mount SquashFS filesystem
mkdir /tmp/squashfs_root
unsquashfs -d /tmp/squashfs_root extracted.squashfs

# Mount CramFS filesystem
mkdir /tmp/cramfs_root
mount -t cramfs -o loop extracted.cramfs /tmp/cramfs_root

# Extract JFFS2 filesystem
jefferson extracted.jffs2 -d /tmp/jffs2_root

# Inspect the extracted filesystem
ls -la /tmp/squashfs_root/
find /tmp/squashfs_root -name "*.conf" -o -name "*.cfg" -o -name "*.key"
find /tmp/squashfs_root -name "passwd" -o -name "shadow"

Step 5: String Analysis and Credential Discovery

Search extracted filesystem and raw firmware for sensitive data:

# Extract all printable strings
strings -a firmware.bin > all_strings.txt
strings -n 12 firmware.bin | sort -u > long_strings.txt

# Search for credentials and secrets
grep -rni "password\|passwd\|secret\|api_key\|token" /tmp/squashfs_root/etc/
grep -rni "BEGIN.*PRIVATE KEY" /tmp/squashfs_root/

# Find hardcoded URLs and endpoints
grep -rnoE "https?://[a-zA-Z0-9./?=_-]+" /tmp/squashfs_root/

# Search for certificate files
find /tmp/squashfs_root -name "*.pem" -o -name "*.crt" -o -name "*.key" -o -name "*.p12"

# Identify busybox and service versions
strings /tmp/squashfs_root/bin/busybox | grep "BusyBox v"
cat /tmp/squashfs_root/etc/banner 2>/dev/null

Step 6: Generate Firmware Analysis Report

Compile comprehensive extraction and analysis findings:

Report should include:
- Firmware metadata (vendor, model, version, build date)
- Identified components with offsets and sizes (bootloader, kernel, filesystem, config)
- Entropy analysis summary with regions of interest
- Extracted filesystem structure and key contents
- Discovered credentials, keys, certificates
- Identified services, daemons, and their versions
- Known CVEs applicable to identified component versions
- Recommendations for hardening or vulnerability remediation

Key Concepts

Tools & Systems

• binwalk: Primary firmware analysis tool for signature scanning, entropy analysis, and automated extraction of embedded files
• unsquashfs: SquashFS extraction utility for mounting read-only compressed filesystems found in router and IoT firmware
• jefferson: Python tool for extracting JFFS2 flash filesystem images commonly found in embedded devices
• sasquatch: Patched SquashFS utility supporting non-standard vendor-modified SquashFS variants
• firmware-mod-kit: Toolkit for extracting, modifying, and repacking firmware images for security testing

Common Scenarios

Scenario: Extracting and Auditing Router Firmware for Hardcoded Credentials

Context: A security researcher is performing an authorized assessment of a consumer router. The firmware update file was downloaded from the vendor's support page. The goal is to identify hardcoded credentials, insecure default configurations, and known vulnerable components.

Approach:

1. Run binwalk -e firmware.bin to perform initial extraction
2. Use binwalk -E firmware.bin to check entropy and identify encrypted regions
3. Locate the SquashFS root filesystem in the extracted output
4. Mount with unsquashfs and inspect /etc/passwd, /etc/shadow, and web server configs
5. Search for hardcoded credentials with grep -rni "password" /tmp/root/etc/
6. Identify service versions and cross-reference with CVE databases
7. Check for debug interfaces (telnet, UART, JTAG references) in startup scripts
8. Examine web application code for authentication bypass or command injection

Pitfalls:

• Some vendors use non-standard SquashFS with custom compression; use sasquatch instead of unsquashfs
• Encrypted firmware requires decryption keys often found in bootloader or previous unencrypted versions
• Firmware headers may need to be stripped before binwalk can identify the embedded filesystem
• Obfuscated strings may evade simple grep searches; use entropy analysis to locate data blobs

Output Format

FIRMWARE EXTRACTION REPORT
====================================
Firmware:         TP-Link TL-WR841N v14
File:             wr841nv14_en_3_16_9_up.bin
Size:             3,932,160 bytes (3.75 MB)
SHA-256:          a1b2c3d4e5f6...

SIGNATURE SCAN RESULTS
Offset       Type                          Size
------       ----                          ----
0x00000000   U-Boot bootloader header      64 bytes
0x00020000   LZMA compressed data          1,048,576 bytes
0x00120000   SquashFS filesystem v4.0      2,752,512 bytes
0x003B0000   Configuration partition       131,072 bytes

ENTROPY ANALYSIS
Region 0x000000-0x020000: 4.21 (bootloader - plaintext code)
Region 0x020000-0x120000: 7.89 (kernel - LZMA compressed)
Region 0x120000-0x3B0000: 7.45 (filesystem - SquashFS compressed)
Region 0x3B0000-0x3C0000: 1.12 (config - mostly empty)

EXTRACTED FILESYSTEM
Root filesystem: SquashFS v4.0, LZMA compression
Total files: 847
Total dirs: 112
BusyBox version: 1.19.4

SECURITY FINDINGS
[CRITICAL] Hardcoded root password in /etc/shadow (hash: $1$...)
[HIGH]     Telnet daemon enabled by default in /etc/init.d/rcS
[HIGH]     Private RSA key at /etc/ssl/private/server.key
[MEDIUM]   BusyBox 1.19.4 (CVE-2021-42373, CVE-2021-42374)
[MEDIUM]   Dropbear SSH 2014.63 (CVE-2016-3116)
[LOW]      UPnP service enabled by default

Other files in this skill

• LICENSE
• references/api-reference.md
• scripts/agent.py

references/api-reference.md (verbatim)

API Reference: Binwalk Firmware Extraction Tools

binwalk - Firmware Analysis Tool

Signature Scan

binwalk firmware.bin                      # Basic signature scan
binwalk -v firmware.bin                   # Verbose output
binwalk -B firmware.bin                   # Explicit signature scan flag
binwalk -A firmware.bin                   # Opcode/architecture scan
binwalk -R "string" firmware.bin          # Raw string search

Extraction

binwalk -e firmware.bin                   # Extract known file types
binwalk -Me firmware.bin                  # Recursive (matryoshka) extraction
binwalk -Me -d 5 firmware.bin             # Recursive with depth limit
binwalk -C /output/dir -e firmware.bin    # Custom output directory
binwalk -D "type:ext:cmd" firmware.bin    # Custom extraction rule

Entropy Analysis

binwalk -E firmware.bin                   # Entropy analysis with plot
binwalk -E -K 256 firmware.bin            # Custom block size
binwalk -BE firmware.bin                  # Combined signature + entropy

Key Flags

unsquashfs - SquashFS Extraction

Syntax

unsquashfs -d /output/dir image.squashfs          # Extract to directory
unsquashfs -l image.squashfs                       # List contents
unsquashfs -ll image.squashfs                      # Long listing
unsquashfs -s image.squashfs                       # Show superblock info
unsquashfs -f -d /output image.squashfs            # Force overwrite

Key Flags

jefferson - JFFS2 Extraction

Syntax

jefferson image.jffs2 -d /output/dir              # Extract JFFS2
jefferson -v image.jffs2 -d /output/dir            # Verbose extraction

sasquatch - Vendor SquashFS

Syntax

sasquatch -d /output/dir image.squashfs            # Extract non-standard SquashFS
sasquatch -p 1 -d /output image.squashfs           # Single-threaded extraction

Handles vendor-modified SquashFS variants from TP-Link, D-Link, Netgear, and others that use non-standard compression or block sizes.

strings - String Extraction

Syntax

strings firmware.bin                               # Default (4+ chars)
strings -n 12 firmware.bin                         # Minimum 12 chars
strings -a firmware.bin                            # Scan entire file
strings -t x firmware.bin                          # Show hex offsets
strings -e l firmware.bin                          # Little-endian 16-bit

Key Flags

dd - Manual Extraction

Syntax

dd if=firmware.bin of=output.bin bs=1 skip=OFFSET count=SIZE
dd if=firmware.bin of=output.bin bs=1 skip=$((0x120000)) count=$((0x2A0000))

Key Parameters

Python binwalk Module (v2 API)

Programmatic Usage

import binwalk

# Signature scan
for module in binwalk.scan(firmware_path, signature=True, quiet=True):
    for result in module.results:
        print(f"0x{result.offset:08X}  {result.description}")

# Extract files
binwalk.scan(firmware_path, signature=True, extract=True, quiet=True)

# Entropy analysis
for module in binwalk.scan(firmware_path, entropy=True, quiet=True):
    for result in module.results:
        print(f"0x{result.offset:08X}  entropy={result.entropy}")

# Recursive extraction
binwalk.scan(firmware_path, signature=True, extract=True,
             matryoshka=True, depth=5, quiet=True)

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