mcp-shell: Secure Mode Allowlist Bypass via Default `/bin/bash` Executable

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-55581
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-08-25 16:16:55 UTC
Updated2026-09-09 21:07:31 UTC
Descriptionmcp-shell is an MCP server for running shell commands securely, auditably, and on demand. Prior to 0.6.0, the default Docker security.yaml includes /bin/bash in allowed_executables, while security.go validates only the first token and checkBlockedPatternsAndCommands does not reject the shell command-mode flag -c. A caller of the shell_exec MCP tool can provide the command argument `/bin/bash -c <arbitrary-command>`, which passes validation and reaches executor.go, where parseCommand and exec.CommandContext execute the arbitrary command as mcpuser outside the intended allowlist. This issue is fixed in version 0.6.0.

Risk And Classification

Primary CVSS: v3.1 8.4 HIGH from [email protected]

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

EPSS: 0.003400000 probability, percentile 0.270920000 (date 2026-09-10)

Problem Types: CWE-78 | CWE-183 | CWE-1188 | CWE-78 CWE-78: Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection') | CWE-183 CWE-183: Permissive List of Allowed Inputs | CWE-1188 CWE-1188: Insecure Default Initialization of Resource

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary8.4HIGHCVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
3.1CNADECLARED8.4HIGHCVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS v3.1 Breakdown

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

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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Sonirico Mcp-shell affected < 0.6.0 Not specified

References

ReferenceSourceLinkTags
github.com/sonirico/mcp-shell/security/advisories/GHSA-3x77-wg38-92r3 134c704f-9b21-4f2e-91b3-4a467353bcc0 github.com
github.com/sonirico/mcp-shell/commit/f31377fce6ec31114e5a4398c0e5270552b... [email protected] github.com
github.com/sonirico/mcp-shell/pull/16 [email protected] github.com
github.com/sonirico/mcp-shell/releases/tag/v0.6.0 [email protected] github.com
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