reverse-skills-max: initial public release (restored, redacted, hardened)

vendor-new/analyst-ai-pack/skills/analyzing-mach-o-binaries-on-macos/SKILL.md

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+---
+name: analyzing-mach-o-binaries-on-macos
+description: 'Statically analyzes macOS Mach-O malware: parsing the header and load commands,
+  handling fat/universal binaries, reading linked dylibs and entitlements, and checking code
+  signatures to infer capability and trust. Activates for requests to analyze a Mach-O binary,
+  inspect macOS malware, or parse load commands and entitlements.'
+domain: cybersecurity
+subdomain: malware-analysis
+tags:
+  - malware-analysis
+  - mach-o
+  - macos
+  - static-analysis
+  - code-signing
+version: 1.0.0
+author: analyst-ai-pack
+license: Apache-2.0
+mitre_attack:
+  - T1027
+  - T1059.002
+d3fend:
+  - D3-FCR
+  - D3-DA
+references:
+  - 'Apple Mach-O file format reference — https://github.com/apple-oss-distributions/xnu/blob/main/EXTERNAL_HEADERS/mach-o/loader.h'
+  - 'macOS code signing overview — https://developer.apple.com/documentation/security/code_signing_services'
+---
+
+# Analyzing Mach-O Binaries on macOS
+
+## When to Use
+
+- You have a macOS sample (Mach-O) and need a static capability and trust read.
+- You must handle a fat/universal binary containing multiple architecture slices.
+- You need to inspect linked dylibs, entitlements, and code-signing status.
+
+**Do not use** Windows PE tooling on Mach-O — the formats differ entirely; use Mach-O-aware
+parsers.
+
+## Prerequisites
+
+- A Mach-O parser (Python stdlib `struct`, or `macholib`/LIEF); the sample handled inertly.
+- For signing/entitlements on macOS, `codesign`/`otool` are authoritative.
+
+## Safety & Handling
+
+- Parse statically; never execute the sample, especially on a real macOS host.
+- Keep the sample password-protected at rest and reference it by hash.
+
+## Workflow
+
+### Step 1: Detect fat vs. thin and architecture
+
+Check the magic: `0xCAFEBABE` (fat/universal) vs. `0xFEEDFACE`/`0xFEEDFACF` (Mach-O 32/64). For
+fat binaries, enumerate and analyze each slice.
+
+```bash
+python scripts/analyst.py header sample.macho
+```
+
+### Step 2: Parse load commands
+
+Read load commands for linked dylibs (`LC_LOAD_DYLIB`), entry point (`LC_MAIN`), and signing
+(`LC_CODE_SIGNATURE`). The dylib list hints at capability (networking, crypto).
+
+### Step 3: Inspect entitlements and signing
+
+On macOS, use `codesign`/`otool` to read entitlements and verify the signature. Ad-hoc or absent
+signatures and suspicious entitlements are risk indicators.
+
+### Step 4: Infer capability and route
+
+Map linked frameworks/symbols to behaviors and route to disassembly/RE for deeper analysis.
+
+## Validation
+
+- Fat binaries are decomposed and each slice is analyzed, not just the first.
+- Load commands, dylibs, and signing status are enumerated correctly.
+- Capability inferences are corroborated by linked frameworks/symbols.
+
+## Pitfalls
+
+- Analyzing only one slice of a universal binary.
+- Trusting a present signature without verifying it (ad-hoc signatures verify but aren't trusted).
+- Applying PE assumptions (sections/imports) to Mach-O structures.
+
+## References
+
+- See [`references/api-reference.md`](references/api-reference.md) for the Mach-O header parser.
+- Apple Mach-O loader.h and code signing docs (linked in frontmatter).