MGS2007: exec denied by sandbox

A spell tried to execute a binary whose resolved path is outside every path the policy grants exec on.

[MGS2007] exec denied: /home/user/Downloads/exfil

Why

Exec is a grant of its own: a path the sandbox lets a step read is not thereby a path it may run. The default policy grants exec on the workspace, the private temp dir, the system trees (/usr, /bin, /sbin, /lib*, /opt, /nix/store), each absolute PATH entry other than $HOME and its ancestors, toolchain install roots (GOROOT, rustup, cargo's bin, mise, asdf) and the magus binary. This blocks the attack pattern of dropping a small binary into ~/ and running it.

The binary path is the one exec.LookPath returns, resolved through its symlinks, so an unqualified curl found at /usr/bin/curl is allowed.

Resolution

• Built-in spells: should never trigger this. If they do, file a bug.

• A tool you installed somewhere the default does not cover: grant its directory read and exec:

  sandbox:
    allow:
      - path: ~/tools/bin
        mode: rx
  

  ro is not enough: exec is never implied by read.

• A spell dropping and running a binary: do not extend the allowlist. This is the sandbox working as designed.