Poisoning Claude Code: One GitHub Issue to Break the Supply Chain

Mon, 01 Jun 2026 00:00:00 +0000

Introduction

Hello, I’m RyotaK ( @ryotkak ), a security researcher at GMO Flatt Security Inc.

After publishing my previous article ( Pwning Claude Code in 8 Different Ways ), I continued investigating Claude-related products and found several more vulnerabilities.

In this article, I will explain a vulnerability in Claude Code’s GitHub Actions that could allow an attacker to compromise any repository that uses the Claude Code workflow, including Anthropic’s own repositories.¹

Note: Variants of the misconfiguration issues described in this article were actively exploited in the wild before this article was published.

GitHub Actions on GMO Flatt Security Research

Poisoning Claude Code: One GitHub Issue to Break the Supply Chain

Introduction