VulnerabilityPublished 9 Jul 2026

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

Affects phantom-audioSource GCVE Database

Mentioned vulnerabilities

CVE-2026-37555

CVSS 7.7 High : upgrade to 1.3.1 soon.

Data as of 10 Jul 2026, 09:29 UTC

CVSS 3.1 base score

7.7High

How severe the flaw is on the 0–10 CVSS scale.

Patch: Available – fixed in 1.3.1

CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Attack Vector: Local
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: High
Integrity: High
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Local: The vulnerable component is not bound to the network stack and the attacker’s path is via read/write/execute capabilities. Either: the attacker exploits the vulnerability by accessing the target system locally (e.g., keyboard, console), or remotely (e.g., SSH); or the attacker relies on User Interaction by another person to perform actions required to exploit the vulnerability (e.g., tricking a legitimate user into opening a malicious document).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: High: There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact.
Integrity: High: There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

What to do

Upgrade phantom-audio to 1.3.1.

Affected software

Product	Affected	Fixed in
PyPIphantom-audio	Affected <1.3.1	Fixed in 1.3.1

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AI-suggested

A fix is available in Phantom version 1.3.1. Users should upgrade to 1.3.1 or later to ensure file writes are confined to PHANTOM_OUTPUT_DIR and decode operations have appropriate size and duration limits. As a workaround before upgrading, set PHANTOM_OUTPUT_DIR (and optionally PHANTOM_AUDIO_DIR) to dedicated directories prior to starting the server to limit exposure.

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.

Impact

An attacker able to send tool calls to the MCP interface can write or overwrite arbitrary files writable by the Phantom process user, including shell startup files and Reaper __startup.lua, enabling local code execution on developer workstations. Additionally, specially crafted compressed audio files can cause memory exhaustion denial-of-service due to unbounded decoding expansion. This also increases risk from decoder vulnerabilities such as CVE-2026-37555. These impacts can lead to system compromise and service disruption.

Summary

In Phantom <= 1.3.0, when PHANTOM_OUTPUT_DIR is unset, MCP tools accept arbitrary absolute output paths without confinement, enabling arbitrary file write by any entity able to send tool calls. This can overwrite critical user files such as shell startup scripts or Reaper __startup.lua files, effectively allowing local code execution on developer workstations. Separately, the stem-separation and render audio decode paths lack size and duration caps, allowing small compressed FLAC/OGG files to expand into multi-gigabyte PCM data, causing memory exhaustion denial-of-service and increasing exposure to decoder bugs like CVE-2026-37555 in libsndfile. The issues are addressed in Phantom 1.3.1 by confining file writes to PHANTOM_OUTPUT_DIR with symlink resolution and re-verification, adding decode/duration/size limits to separation and render paths, and hardening file creation and input reads against TOCTOU race conditions.

CWE-22Improper Limitation of a Pathname to a Restricted Directory (Path Traversal) (opens in a new tab)
Base weaknessLikelihood of exploit: HighCWE Top 25 (2025): #6OWASP Top 10 A01:2025: Broken Access Control (opens in a new tab)
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.
Implementation · Input Validation
Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
Architecture and Design
For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks…
Implementation · Input Validation
Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180). Make sure that the application does not decode the same input twice (CWE-174).
OWASP Cheat Sheets
Authorization (opens in a new tab)
OWASP ASVS 4.0.3
V12.3.1 (opens in a new tab)
Attack patterns
Path Traversal (opens in a new tab)
Using Slashes and URL Encoding Combined to Bypass Validation Logic (opens in a new tab)
Manipulating Web Input to File System Calls (opens in a new tab)
Using Escaped Slashes in Alternate Encoding (opens in a new tab)
Using Slashes in Alternate Encoding (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).
CWE-400Uncontrolled Resource Consumption (opens in a new tab)
Class weaknessLikelihood of exploit: High
The product does not properly control the allocation and maintenance of a limited resource.
MITRE discourages mapping vulnerabilities to this broad entry; the root cause is usually a more specific weakness.
Architecture and Design
Design throttling mechanisms into the system architecture. The best protection is to limit the amount of resources that an unauthorized user can cause to be expended. A strong authentication and access control model will help prevent such attacks from occurring in the first place.
Architecture and Design
Mitigation of resource exhaustion attacks requires that the target system either: recognizes the attack and denies that user further access for a given amount of time, or; uniformly throttles all requests in order to make it more difficult to consume resources more quickly than they can again be freed.
Architecture and Design
Ensure that protocols have specific limits of scale placed on them.
OWASP Cheat Sheets
File Upload (opens in a new tab)
OWASP ASVS 4.0.3
V12.1.1 (opens in a new tab)
Attack patterns
XML Ping of the Death (opens in a new tab)
Regular Expression Exponential Blowup (opens in a new tab)
Sustained Client Engagement (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).
CWE-73External Control of File Name or Path (opens in a new tab)
Base weaknessLikelihood of exploit: HighOWASP Top 10 A06:2025: Insecure Design (opens in a new tab)
The product allows user input to control or influence paths or file names that are used in filesystem operations.
Architecture and Design
When the set of filenames is limited or known, create a mapping from a set of fixed input values (such as numeric IDs) to the actual filenames, and reject all other inputs. For example, ID 1 could map to "inbox.txt" and ID 2 could map to "profile.txt".
Architecture and Design · Operation
Run your code in a "jail" or similar sandbox environment that enforces strict boundaries between the process and the operating system. This may effectively restrict all access to files within a particular directory.
Architecture and Design
For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks…
OWASP Cheat Sheets
XML Security (opens in a new tab)
Mass Assignment (opens in a new tab)
Secure Design Principles (opens in a new tab)
OWASP ASVS 4.0.3
V12.3.2 (opens in a new tab)
V13.3.1 (opens in a new tab)
V5.1.4 (opens in a new tab)
Attack patterns
Subverting Environment Variable Values (opens in a new tab)
Leverage Alternate Encoding (opens in a new tab)
Using Slashes and URL Encoding Combined to Bypass Validation Logic (opens in a new tab)
URL Encoding (opens in a new tab)
Manipulating Web Input to File System Calls (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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What to do

Affected software

Description

AI analysisMachine-generated, updated 9 Jul 2026, 14:02 UTC

WeaknessesCWE-22, CWE-400, CWE-73

Technical details

References

Community reviews

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