brew-cask: refusing to stage cask payload through a path out

Error message

brew-cask: refusing to stage cask payload through a path outside the caskroom: {}

What it means

A security guard during cask payload staging: the computed destination (caskroom joined with the staged relative path) does not resolve to a location inside the caskroom, likely due to symlink traversal or '..' components. mise bails instead of writing outside the caskroom.

Source

Thrown at src/system/packages/brew/cask/mod.rs:3110

        .iter()
        .filter_map(|app| find_app(stage, &app.source))
        .map(|source| file::desymlink_path(&source))
        .collect();
    for entry in std::fs::read_dir(stage)? {
        let source = entry?.path();
        if !path_starts_with_resolved_root(&source, stage) {
            continue;
        }
        let resolved = file::desymlink_path(&source);
        if app_sources.contains(&resolved) {
            continue;
        }
        let Some(relative) = staged_relative_path(stage, &source) else {
            continue;
        };
        let target = caskroom.join(&relative);
        if !path_starts_with_resolved_root(&target, caskroom) {
            bail!(
                "brew-cask: refusing to stage cask payload through a path outside the caskroom: {}",
                target.display()
            );
        }
        if target.symlink_metadata().is_ok() {
            continue;
        }
        if let Some(parent) = target.parent() {
            file::create_dir_all(parent)?;
        }
        if source.is_dir() {
            file::copy_dir_all_preserve_symlinks(&source, &target)?;
        } else {
            file::copy(&source, &target)?;
        }
    }
    Ok(())
}

View on GitHub (pinned to afd2eddd3a)

Solutions

Remove any '..' components or symlink indirection from the staged payload paths
Inspect the caskroom for pre-existing symlinks pointing outside it and delete them
Re-extract the cask archive from a trusted source and retry the install

Example fix

// before
relative = "../../etc/foo" // escapes caskroom
// after
relative = "scripts/foo" // stays under caskroom

Defensive patterns

Strategy: validation

Validate before calling

let target = caskroom.join(&relative);
if !target.starts_with(&caskroom) || relative.components().any(|c| c == Component::ParentDir) {
    return Err("payload path escapes the caskroom");
}

Prevention

Reject any payload entry containing '..' at archive extraction time
Avoid placing symlinks inside the caskroom that point outside it
Verify stage and caskroom roots are real directories, not symlinked into other trees

When it happens

Trigger: Staging a cask payload file whose relative path escapes the caskroom via '..' components or a symlink inside the caskroom pointing elsewhere, detected by path_starts_with_resolved_root before any write.

Common situations: Crafted or corrupted cask archives containing path-traversal entries, a previously created symlink in the caskroom redirected at another directory, or a stage root itself being a symlink into a different tree.

Understand the failure class

Background: Path traversal blocked: "path escapes the workspace" and "outside site root" errors when a path will not stay inside its allowed directory — this error's family across 26 libraries.

Related errors

AI-assisted analysis of jdx/mise@afd2eddd3a (2026-09-09). Data as JSON: /api/errors/77abecf29da5c6e3. Report an issue: GitHub.