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Phantom: Arbitrary file write and decode-bomb DoS via unconfined MCP tool paths

High severity GitHub Reviewed Published Jun 1, 2026 in fadelabs/phantom • Updated Jul 9, 2026

Package

pip phantom-audio (pip)

Affected versions

<= 1.3.0

Patched versions

1.3.1

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_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.

References

@leesaenz leesaenz published to fadelabs/phantom Jun 1, 2026
Published to the GitHub Advisory Database Jul 9, 2026
Reviewed Jul 9, 2026
Last updated Jul 9, 2026

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Local
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

EPSS score

Weaknesses

Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')

The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory. Learn more on MITRE.

External Control of File Name or Path

The product allows user input to control or influence paths or file names that are used in filesystem operations. Learn more on MITRE.

Uncontrolled Resource Consumption

The product does not properly control the allocation and maintenance of a limited resource. Learn more on MITRE.

CVE ID

No known CVE

GHSA ID

GHSA-52vm-mxx8-f227

Source code

Credits

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