CVE-2026-5058: aws-mcp-server RCE Vulnerability

CVE-2026-5058 Overview

CVE-2026-5058 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 authentication. The flaw exists within the handling of the allowed commands list, where improper validation of user-supplied strings before executing system calls creates a severe security exposure.

Critical Impact

Unauthenticated remote attackers can execute arbitrary code in the context of the MCP server, potentially leading to complete system compromise, data exfiltration, and lateral movement within cloud infrastructure.

Affected Products

• aws-mcp-server (all versions prior to patch)

Discovery Timeline

• 2026-04-11 - CVE-2026-5058 published to NVD
• 2026-04-13 - Last updated in NVD database

Technical Details for CVE-2026-5058

Vulnerability Analysis

This command injection vulnerability (CWE-78) represents a fundamental input validation failure in aws-mcp-server's command processing functionality. The vulnerability is accessible over the network without requiring authentication or user interaction, making it particularly dangerous for exposed MCP server deployments. An attacker exploiting this flaw gains code execution privileges within the MCP server context, which typically has elevated access to AWS resources and credentials.

The vulnerability was tracked by the Zero Day Initiative as ZDI-CAN-27968 and published as ZDI-26-246.

Root Cause

The root cause of CVE-2026-5058 is the lack of proper validation and sanitization of user-supplied strings before they are used in system call execution. The allowed commands list handling mechanism fails to adequately filter or escape potentially malicious input, allowing attackers to inject arbitrary commands that are subsequently executed by the underlying system.

Attack Vector

The attack vector is network-based, requiring no authentication or user interaction. An attacker can craft malicious input that bypasses the allowed commands list validation and injects arbitrary system commands. These injected commands execute with the privileges of the MCP server process, potentially providing access to AWS credentials, environment variables, and other sensitive resources managed by the server.

The vulnerability manifests in the command processing pipeline where user-supplied strings are concatenated or passed directly to system execution functions without proper sanitization. Attackers can leverage shell metacharacters or command separators to break out of the intended command context and execute arbitrary code. For detailed technical analysis, refer to the ZDI-26-246 advisory.

Detection Methods for CVE-2026-5058

Indicators of Compromise

• Unusual process spawning from the aws-mcp-server process, particularly shell interpreters like /bin/sh, /bin/bash, or cmd.exe
• Unexpected network connections originating from the MCP server to external IP addresses
• AWS API calls or credential access patterns that deviate from normal MCP server behavior
• Log entries showing malformed or suspicious command strings containing shell metacharacters (;, |, &&, $(), backticks)

Detection Strategies

• Monitor aws-mcp-server process execution for child processes that are inconsistent with normal operations
• Implement network segmentation and monitor for anomalous outbound connections from MCP server hosts
• Deploy application-level logging to capture and analyze incoming requests to the MCP server
• Use endpoint detection and response (EDR) solutions to identify command injection patterns and suspicious process chains

Monitoring Recommendations

• Enable comprehensive logging for all aws-mcp-server instances and forward logs to a centralized SIEM
• Configure alerts for any shell command execution patterns containing injection indicators
• Monitor AWS CloudTrail for unusual API activity that may indicate compromised MCP server credentials
• Implement file integrity monitoring on MCP server configuration files and binaries

How to Mitigate CVE-2026-5058

Immediate Actions Required

• Restrict network access to aws-mcp-server instances using firewall rules and network segmentation
• Implement Web Application Firewall (WAF) rules to filter requests containing command injection patterns
• Review and audit all aws-mcp-server deployments for exposure to untrusted networks
• Rotate any AWS credentials that may have been accessible through potentially compromised MCP servers

Patch Information

Refer to the Zero Day Initiative advisory ZDI-26-246 for vendor patch information and updates. Monitor the official aws-mcp-server repository and distribution channels for security releases addressing this vulnerability.

Workarounds

• Implement strict network access controls limiting MCP server exposure to trusted internal networks only
• Deploy input validation at the network perimeter to reject requests containing shell metacharacters
• Run aws-mcp-server in a containerized or sandboxed environment with minimal privileges and restricted system call access
• Consider disabling or removing affected command processing functionality if not required for operations

# Example network restriction using iptables
# Restrict MCP server access to trusted internal network only
iptables -A INPUT -p tcp --dport 3000 -s 10.0.0.0/8 -j ACCEPT
iptables -A INPUT -p tcp --dport 3000 -j DROP