GHSA-52vm-mxx8-f227 Phantom: Arbitrary file write and decode-bomb DoS via unconfined MCP tool paths
Attackers can write arbitrary files or cause DoS via unconfined paths and missing decode limits in Phantom MCP tools, enabling local code execution.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is GHSA-52vm-mxx8-f227?
GHSA-52vm-mxx8-f227 is a path traversal vulnerability in phantom-audio, published on 9 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
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_EXCLoutput 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.
Which versions are affected by GHSA-52vm-mxx8-f227?
2 open source packages ship an affected version, including phantom-audio.
| Package | Affected | Fixed in |
|---|---|---|
phantom-audio PyPI | All versions | 1.3.1 |
phantom-audio PyPI | All versions | 1.3.1 |
How do I fix GHSA-52vm-mxx8-f227?
Upgrade phantom-audio to 1.3.1 or later.
Upgrade, and resolve every user-supplied path against an allowed base folder before opening it. More about Path traversal.
Is GHSA-52vm-mxx8-f227 being exploited?
There is no known exploitation of GHSA-52vm-mxx8-f227 in the wild and no public exploit code.