CVE-2026-5059: aws-mcp-server Command Injection RCE Flaw

CVE-2026-5059 Overview

CVE-2026-5059 is a critical command injection vulnerability affecting aws-mcp-server that enables remote code execution. This vulnerability allows remote attackers to execute arbitrary code on affected installations of aws-mcp-server without requiring authentication.

The specific flaw exists within the handling of the allowed commands list. The issue results from the lack of proper validation of a user-supplied string before using it to execute a system call. An attacker can leverage this vulnerability to execute code in the context of the MCP server.

Critical Impact

Unauthenticated attackers can achieve remote code execution on aws-mcp-server installations by exploiting improper input validation in the allowed commands handling, potentially leading to complete system compromise.

Affected Products

• aws-mcp-server (all versions prior to patched release)

Discovery Timeline

• 2026-04-11 - CVE-2026-5059 published to NVD
• 2026-04-13 - Last updated in NVD database

Technical Details for CVE-2026-5059

Vulnerability Analysis

This vulnerability is classified as CWE-78 (Improper Neutralization of Special Elements used in an OS Command), commonly known as OS Command Injection. The aws-mcp-server component fails to properly sanitize user-supplied input before incorporating it into system command executions. The flaw is accessible over the network without authentication, making it particularly dangerous for exposed deployments.

The vulnerability exists within the command handling mechanism where the allowed commands list is processed. When an attacker supplies specially crafted input, the lack of proper validation allows malicious commands to be injected and executed within the context of the MCP server process.

Root Cause

The root cause of this vulnerability is insufficient input validation and sanitization of user-supplied strings in the allowed commands list handling. The application directly passes user-controlled data to system call functions without properly escaping or validating the input for shell metacharacters and command separators.

Attack Vector

The attack vector is network-based and requires no authentication or user interaction. An attacker can remotely send a specially crafted request to the aws-mcp-server that includes malicious command sequences. Due to the lack of input validation, these commands are interpreted and executed by the underlying system shell in the security context of the MCP server process.

The exploitation process involves injecting shell metacharacters (such as ;, |, &&, or backticks) along with arbitrary commands into the user-supplied string that is passed to the allowed commands handler. When the server processes this input, it inadvertently executes the injected commands alongside or instead of the intended operations.

For detailed technical information regarding exploitation techniques, refer to the Zero Day Initiative Advisory ZDI-26-245.

Detection Methods for CVE-2026-5059

Indicators of Compromise

• Unusual process spawning from the aws-mcp-server process, particularly shell processes (/bin/sh, /bin/bash, cmd.exe)
• Unexpected network connections originating from the MCP server to external hosts
• Anomalous command execution patterns in system logs related to the aws-mcp-server service
• Presence of suspicious files or scripts in directories accessible by the MCP server process

Detection Strategies

• Monitor for command injection patterns in incoming requests to aws-mcp-server endpoints, particularly looking for shell metacharacters (;, |, &&, `, $())
• Implement application-layer firewall rules to detect and block requests containing OS command injection attempts
• Deploy endpoint detection solutions to identify anomalous child process creation from the MCP server
• Review server logs for unusual input patterns or error messages indicating command parsing failures

Monitoring Recommendations

• Enable verbose logging on aws-mcp-server installations to capture all incoming requests and processed commands
• Configure SIEM alerts for process execution anomalies associated with the MCP server service account
• Implement network traffic monitoring to detect data exfiltration attempts following potential exploitation
• Establish baseline behavioral profiles for the MCP server to identify deviations indicating compromise

How to Mitigate CVE-2026-5059

Immediate Actions Required

• Restrict network access to aws-mcp-server installations, limiting exposure to trusted networks only
• Implement network segmentation to isolate MCP server deployments from critical infrastructure
• Deploy web application firewall (WAF) rules to filter command injection patterns in incoming requests
• Review and audit current aws-mcp-server deployments to identify potentially compromised systems

Patch Information

Organizations should monitor vendor communications and the Zero Day Initiative Advisory ZDI-26-245 for official patch availability. Apply security updates as soon as they become available from the vendor.

Workarounds

• Implement strict input validation at the network perimeter using WAF or reverse proxy solutions to sanitize incoming requests
• Restrict the aws-mcp-server service to run with minimal privileges using principle of least privilege
• Deploy application whitelisting to prevent unauthorized command execution from the MCP server process
• Consider temporarily disabling the aws-mcp-server service if it is not critical to operations until a patch is available

# Network isolation example - restrict access to aws-mcp-server
iptables -A INPUT -p tcp --dport <mcp-server-port> -s <trusted-network> -j ACCEPT
iptables -A INPUT -p tcp --dport <mcp-server-port> -j DROP