Sep 11, 2025 - 5 ' read
Pwning the Entire Nix Ecosystem
last year at nixcon, me and my friend lexi gave a lightning talk about how we found a vulnerability in nixpkgs that would have allowed us to pwn pretty much the entire nix ecosystem and inject malicious code into nixpkgs. it only took us about a day from starting our search to reporting it and getting it fixed. since i unfortunately was too sick to attend this years nixcon, i thought it might be a good time to write up what we found and how we did it.
github actions: the easy target #
github actions is a ci/cd system by github that can do pretty much anything in a repo. it’s an easy target for attackers because if you have access to a workflow, you can just commit code without authorization and then you have a supply chain attack. plus, it’s all written in yaml 🇳🇴, which was NEVER meant to be executed !!
name : learn-github-actions on : [ push ] jobs : check-bats-version : runs-on : ubuntu-latest steps : - uses : actions/checkout@v4 - uses : actions/setup-node@v4 - run : npm install -g bats - run : bats -v
this is a simple example of a github action. nothing fancy, just running some commands when code is pushed.
the dangerous pull_request_target #
actions run when a trigger activates them. there are a bunch of different triggers like pushes, commits, or pull requests. but there’s a special one called pull_request_target that has a few critical differences from regular pull_request .
crucially, unlike pull_request , pull_request_target has read/write and secret access by default, even on pull requests from forks. this isn’t vulnerable by itself, but things go south when you start trusting user input from those PRs.
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