Vulnerability · Published Aug 25, 2026 · Assigned by GitHub_M

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

High 8.4

In plain English

A high-severity OS command injection in mcp-shell from sonirico. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 40% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)8.4High

Exploit odds (30 days)0.5%top 60.4% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack toolingNoneno public tooling known

Official 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 packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Go	github.com/sonirico/mcp-shell	0.6.0	GHSA-3x77-wg38-92r3
Go	github.com/sonirico/mcp-shell	0.6.0	GO-2026-6290

Affected products (as reported)

Vendor	Product	Versions
sonirico	mcp-shell	< 0.6.0

Weakness: CWE-78, CWE-183, CWE-1188 · Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

References

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