CVE-2026-85660
Received Received - Intake

Command Substitution Bypass in cli-mcp-server

Publication date: 2026-09-04

Last updated on: 2026-09-04

Assigner: VulnCheck

Description
cli-mcp-server 0.2.5 contains a command allowlist bypass vulnerability in the _validate_command_with_operators function when ALLOW_SHELL_OPERATORS is enabled. Attackers can use shell command substitution syntax like $(...) or backticks to execute non-allowlisted commands that bypass the ALLOWED_COMMANDS validation check.

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Meta Information

Published
2026-09-04
Last Modified
2026-09-04
Generated
2026-09-04
AI Q&A
2026-09-04
EPSS Evaluated
N/A
NVD
CVE-2026-85660
EUVD
EUVD-2026-71116

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
mladensu cli_mcp_server to 0.2.5 (inc)

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-78 The product constructs all or part of an OS command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended OS command when it is sent to a downstream component.

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Executive Summary

cli-mcp-server 0.2.5 has a command allowlist bypass vulnerability in the _validate_command_with_operators function when ALLOW_SHELL_OPERATORS is enabled. Attackers can use shell command substitution like $(...) or backticks to execute non-allowlisted commands that bypass the ALLOWED_COMMANDS validation check.

Detection Guidance

Check if cli-mcp-server 0.2.5 or earlier is installed by running: pip show cli-mcp-server. If installed, verify if ALLOW_SHELL_OPERATORS is enabled in the server configuration. Test for the vulnerability by attempting command substitution syntax like $(whoami) or `whoami` in allowed commands. Monitor server logs for unexpected command executions or security policy violations.

Impact Analysis

This vulnerability allows attackers to execute arbitrary OS commands on the server where cli-mcp-server is running. It can lead to unauthorized data access, system compromise, or further network infiltration depending on the server's permissions and environment.

Compliance Impact

This vulnerability could lead to unauthorized data access or exfiltration, violating GDPR's data protection requirements and HIPAA's security rules for protected health information. Organizations using affected versions may face compliance violations and regulatory penalties.

Mitigation Strategies

Upgrade cli-mcp-server to the latest version if available. Disable ALLOW_SHELL_OPERATORS in the server configuration. Review and restrict ALLOWED_COMMANDS to only necessary commands. Implement additional security controls like command timeout and path validation. Monitor for any signs of exploitation in logs.

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