CVE-2026-55582
mcp-shell: Secure Mode Allowlist Bypass via Git Shell Alias
- State
- Published
- Severity
- 8.4 High
- Published
- Aug 25, 2026
- Updated
- Aug 28, 2026
- Reserved
- Jun 16, 2026
Description
mcp-shell is an MCP server for running shell commands securely, auditably, and on demand. Prior to 0.6.0, the default security.yaml allows /usr/bin/git, while security.go omits ! from containsShellMetacharacters and containsDangerousShellConstructs and applies no per-executable argument policy. A caller of the shell_exec MCP tool can provide the command argument /usr/bin/git -c alias.pwn=!<arbitrary-command>, causing Git to create a shell alias and execute arbitrary OS commands as the mcp-shell process user. The default Docker image runs as mcpuser with Git installed and secure mode enabled, so the bypass is exploitable in the default deployment without additional authentication beyond MCP connectivity. This issue is fixed in version 0.6.0.
Scores
| CVSS | Score | Vector | Source |
|---|---|---|---|
| 3.1 | 8.4 High | CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H | GitHub_M |
Weaknesses
- CWE-78 Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')
Affected Products
| Product | Versions |
|---|---|
mcp-shellsonirico |
|
References
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