macos-process-injection

macos-process-injection is a skill for Claude Code, Codex from JustineDevs/premortem. It costs 53 tokens per session (3,496 once invoked), scanned A, a copy of macos-process-injection, Apache-2.0.

A guide to injecting code into running macOS programs and loading custom dynamic libraries. It explains techniques involving the dynamic linker, XPC, Mach ports, and Electron apps.

In plain words
What is it for?
Use it for authorized macOS security testing, including library hijacking, process manipulation, and injection research.
Why use it?
It helps security researchers understand why process injection works or fails under macOS protections such as SIP and hardened runtime rules.

Skill for Claude CodeCodex

Written for no agent in particular: nothing here depends on one. Also seen: positional $N argument; installed under .agents/ (shared by several agents).

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/justinedevs/premortem/macos-process-injection
Any agent
npx skills add JustineDevs/premortem --skill macos-process-injection
Clone the repo
git clone --depth 1 https://github.com/JustineDevs/premortem

Made for: Claude Code, Codex.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for macos-process-injection

README.md
[![agentmods](https://agentmods.dev/badge/skills/justinedevs/premortem/macos-process-injection.svg)](https://agentmods.dev/skills/justinedevs/premortem/macos-process-injection)
Your own site
<a href="https://agentmods.dev/skills/justinedevs/premortem/macos-process-injection"><img src="https://agentmods.dev/badge/skills/justinedevs/premortem/macos-process-injection.svg" alt="Measured on agentmods" height="20"></a>
Per session 53 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 3,496 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 1 finding. Scan, not verified.
Origin 100% copy Near-identical to another mod in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5.1 $0.00053 $0.03496
Opus 5 $0.00026 $0.01748
Sonnet 5 $0.00011 $0.00699
Haiku 4.5 $0.00005 $0.00350

Measured 3d ago against content hash 117045a93bf2, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-06, from the pricing page.

Security

Grade A, and why

macos-process-injection scanned grade A with 1 finding against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 3d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Runs shell commandslowCapability

Expected in a hook, worth knowing in a rule or an instructions file.

"require('child_process').execSync('id').toString()"
Origin

This is a copy

100% identical to macos-process-injection — 0 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.

.agents/skills/macos-process-injection/SKILL.md · 385 lines

How it starts

The opening of the file, as written. The whole thing — 385 lines — stays where its author put it; the contents beside it link to each section on GitHub.

SKILL: macOS Process Injection — Expert Attack Playbook

AI LOAD INSTRUCTION: Expert macOS process injection techniques. Covers DYLD_INSERT_LIBRARIES, dylib hijacking (weak/rpath/proxy), XPC PID reuse attacks, Mach port manipulation, MIG abuse, and Electron injection. Base models miss entitlement prerequisites and SIP constraints on injection vectors.

Before going deep, consider loading:

Advanced Reference

Also load DYLIB_XPC_TECHNIQUES.md when you need:

  • Step-by-step dylib hijacking methodology with tooling commands
  • XPC exploitation walkthrough with code examples
  • Mach port technique details and task_for_pid patterns

1. DYLD_INSERT_LIBRARIES INJECTION

The most straightforward injection: set an environment variable that forces the dynamic linker to preload your dylib.

1.1 Requirements and Restrictions

Condition Can Inject? Reason
Normal (non-hardened) binary Yes No restrictions
Hardened Runtime enabled No DYLD strips env vars
Hardened Runtime + com.apple.security.cs.allow-dyld-environment-variables Yes Entitlement explicitly allows it
Apple system binary (SIP-protected) No DYLD env vars stripped by SIP
SUID/SGID binary No DYLD env vars stripped for privilege safety
App Sandbox enabled No Sandbox blocks env var injection

1.2 Basic Injection

# Create malicious dylib
cat > inject.c << 'EOF'
#include <stdio.h>
__attribute__((constructor))
void inject() {
    printf("[+] Injected into PID %d\n", getpid());
    // payload here
}
EOF

# Compile for both architectures
gcc -dynamiclib -o inject.dylib inject.c -arch x86_64 -arch arm64

# Inject into target
DYLD_INSERT_LIBRARIES=./inject.dylib /path/to/target

Read the full file on GitHub · 385 lines

Files

What ships with it

1 file beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 3d ago First seen · 385 lines · 53 tokens per session scan A 117045a93bf2

Subscribe to this mod's changes

macos-process-injection is a skill published in the GitHub repository JustineDevs/premortem (2 stars, last pushed 1mo ago), licensed Apache-2.0. It adds 53 tokens to every session and 3,496 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 1 finding (runs shell commands). It is 100% identical to macos-process-injection, differing in 0 lines, and is treated as a copy.

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