What’s Vulnerable › Vulnerabilities

CVE-2026-55581: mcp-shell: Secure Mode Allowlist Bypass via Default `/bin/bash` Executable

• Severity: high (CVSS 8.4 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-08-25 · updated 2026-09-09
• Weakness: CWE-78

Description

mcp-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.

Affected products

• sonirico mcp-shell: before 0.6.0

References

• https://github.com/sonirico/mcp-shell/commit/f31377fce6ec31114e5a4398c0e5270552bce09f
• https://github.com/sonirico/mcp-shell/pull/16
• https://github.com/sonirico/mcp-shell/releases/tag/v0.6.0
• https://github.com/sonirico/mcp-shell/security/advisories/GHSA-3x77-wg38-92r3
• https://github.com/sonirico/mcp-shell/security/advisories/GHSA-3x77-wg38-92r3

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