Claude Code CVE-2026-39861:sandbox escape via symlink

I identified this in August last year but it was specifically excluded by Anthropic's Vulnerability Disclosure Program Policy at the time.

You can still see the exclusion on HackerOne: https://hackerone.com/anthropic-vdp/policy_scopes

   Out of Scope:

    Abusing intended functionality of Claude CLI
    Using aliased commands, symlinks or other environment-specific settings to bypass permission prompts
    Local storage of Claude Code credentials, configuration and logs

Symlinks have been very important to manage skills from disparate sources and managing multiple CLIs.

Codex did not originally support symlink'd skills but added it in response to user requests on Jan 9th.

Interesting that the submission just before this is about:

Anthropic response to 1-click pwn: Shouldn't have clicked 'ok': https://news.ycombinator.com/item?id=48057836

This makes me think a bit more about this CVE more too.

Anthropic lately has been really trying to burn any/every good will that they have it seems. Also a bit ironical about how the most dangerous model (Mythos) which can find CVE in other projects wasn't able to find this CVE within the claude-code project itself.

And yet Mythos couldn’t find it. Whomp whomp