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“Mythos 5 also hid a prompt injection inside an HTML comment in a GitHub issue. The instruction was invisible on the rendered page but available to coding agents reading the issue through an API. It addressed Claude Code, Codex, and Cursor and told them to download and execute a script.”

Well, uh, how and why is this possible on the GitHub website? This reminds me of invisible ASCII characters, but those at least serve some purpose

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Presumably it’s just because the GitHub markdown engine doesn’t block HTML comments in issues. It’s useful in README files if you’ve got funky tables and need to explain what to change to any contributors.

Seems like they might want to do something about that just for comments.

It’s worth pointing out for people who are not aware of it, you can install the github cli[1] and view, merge, close etc prs and issue from the command-line. As well as (for me at least) being a significant step up in terms of productivity (from having to go to a website to merge a pr or view an issue) that has the advantage that “invisible” text in a PR or issue comment would show up very clearly. (At least in my terminal because it’s not rendering html).

[1] https://cli.github.com/

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