OpenClaw: Sandbox media fallback tmp symlink alias bypass allows host file reads outside sandboxRoot

Summary

### Summary A sandbox path validation bypass in `openclaw` allows host file reads outside `sandboxRoot` via the media path fallback tmp flow when the fallback tmp root is a symlink alias.

### Affected Packages / Versions - Package: `npm openclaw` - Affected versions: `<= 2026.2.24` - Latest published npm version at triage time (February 26, 2026): `2026.2.24` - Patched version : `2026.2.25`

### Details When `/tmp/openclaw` is unavailable or unsafe, `resolvePreferredOpenClawTmpDir()` in `src/infra/tmp-openclaw-dir.ts` fell back to `os.tmpdir()/openclaw-<uid>` without verifying that fallback path was a trusted non-symlink directory.

`resolveSandboxedMediaSource()` (`src/agents/sandbox-paths.ts`) allows absolute tmp media paths under the OpenClaw tmp root using lexical containment and alias checks. If the fallback tmp root is a symlink alias (for example to `/`), inputs like `$TMPDIR/openclaw-<uid>/etc/passwd` can pass validation and resolve to host files outside `sandboxRoot`.

### Impact This can break sandbox media path confinement and permit unauthorized host file reads (confidentiality impact).

### Reproduction (high level) 1. Force resolver fallback (make `/tmp/openclaw` unavailable/invalid). 2. Make fallback root (`$TMPDIR/openclaw-<uid>`) a symlink alias to `/`. 3. Submit media path under fallback root (for example `$TMPDIR/openclaw-<uid>/etc/passwd`). 4. Observe accepted path and read outside `sandboxRoot`.

### Fix Commit(s) - `496a76c03ba85e15ea715e5a583e498ae04d36e3`

### Release Process Note Patched version is pre-set to release `2026.2.25`; once npm publish for `2026.2.25` is complete, this advisory can be published without further metadata edits.

OpenClaw thanks @tdjackey for reporting.