GHSA-52vm-mxx8-f227 Phantom: Arbitrary file write and decode-bomb DoS via unconfined MCP tool paths

• PyPI phantom-audio: < 1.3.1 → fixed in 1.3.1

Impact In Phantom <= 1.3.0, when `PHANTOM_OUTPUT_DIR` was unset (the default), the MCP tools accepted arbitrary absolute output paths with no confinement. Anything able to send tool calls (e.g. an AI agent driving the MCP interface) could write or overwrite arbitrary files the process user can write — including shell startup files (`~/.zshrc`) or a Reaper `__startup.lua`, which is effectively local code execution on a developer workstation. Separately, the stem-separation and render paths decoded input audio with no size/duration cap (the analysis path was already guarded). A small, highly compressed FLAC/OGG could expand to multi-gigabyte PCM, causing memory-exhaustion DoS, and widened exposure to decoder bugs including libsndfile CVE-2026-37555. Patches Fixed in 1.3.1: • File writes are always confined to `PHANTOM_OUTPUT_DIR` (default `~/.phantom/output`); symlinks resolved and re-verified on the final path. • Decode/duration/size guards mirrored onto the separation and render paths (plus ffmpeg `-max_alloc`/`-t`/`-fs`). • Atomic `O_CREAT|O_EXCL` output creation in reference matching and symlink-TOCTOU hardening on confined input reads. Workarounds Set `PHANTOM_OUTPUT_DIR` (and optionally `PHANTOM_AUDIO_DIR`) to dedicated directories before starting the server. Credit Found during an internal security audit.