CVE-2026-5059: aws-mcp-server RCE

Technical Analysis

CVE-2026-5059 identifies a critical OS command injection vulnerability in aws-mcp-server, a tool often used to integrate AWS CLI commands within MCP (Model Context Protocol) environments. The vulnerability allows an unauthenticated remote attacker to execute arbitrary system commands on the server hosting the MCP node.

Given the context in which MCP servers operate—often handling sensitive API credentials and interacting with production cloud infrastructure—the impact is severe.

The vulnerability, assigned CVSS score 9.8, stems from the insecure implementation of the allowed commands list management. Specifically, the application fails to sanitize user-provided strings before incorporating them into a system call.

Exploitation Flow

Successful exploitation results in full remote code execution. Because the MCP server is designed to facilitate interaction with AWS services, the attacker gains immediate access to the environment where the server runs.

Request: The attacker sends a malformed request to the MCP server.
Parsing: The server parses the input to check it against the “allowed commands” list.
Injection: Due to missing input validation, the attacker injects OS command delimiters (e.g., ;, &, |).
Execution: The server executes the malicious payload within the context of the running node process.

Attack Vector

Network (Remote)

Complexity & Auth

Low Complexity / Authentication Not Required

Forensic Investigation

When investigating potential compromise, analysts must focus on identifying anomalous process behavior originating from the MCP server environment.

Process Lineage: Inspect the process tree to identify unexpected shells spawned by the node process.
Log Correlation: Correlate incoming network requests to the MCP server with the creation of these unexpected child processes in Linux execution logs (e.g., Event ID 4688 equivalent in Sysmon for Linux or auditd).

Detection & Threat Hunting

To proactively identify potential exploitation attempts, implement the following detection rules in your SIEM or EDR solutions.

Sigma Rule
Threat Hunting (Splunk/ELK)

title: Suspicious Child Process from AWS-MCP-Server
id: 5e6a9f4c-2b3a-4e8c-8f2a-7d9b3c4f2e1a
status: experimental
description: Detects suspicious child processes (sh, bash, python, curl, etc.) spawned by the aws-mcp-server process, indicating potential OS command injection.
logsource:
    category: process_creation
    product: linux
detection:
    selection_parent:
        ParentImage|endswith: '/node'  # Assuming nodejs runtime for MCP server
    selection_child:
        Image|endswith:
            - '/bin/sh'
            - '/bin/bash'
            - '/usr/bin/python'
            - '/usr/bin/curl'
            - '/usr/bin/wget'
    condition: selection_parent and selection_child
level: critical
tags:
    - attack.execution
    - attack.t1204
    - cve.2026-5059

# Requête Threat Hunting (Splunk/ELK)
# Identifie les exécutions de commandes shell suspectes depuis le processus aws-mcp-server

index=os_logs sourcetype=linux_process_creation
| search ParentProcessName="*node*" AND (ProcessName="*sh" OR ProcessName="*bash" OR ProcessName="*python*" OR ProcessName="*curl*" OR ProcessName="*wget*")
| table _time, host, ParentProcessName, ParentProcessId, ProcessName, ProcessId, CommandLine
| sort - _time

Mitigation

Update: Immediately update aws-mcp-server to the latest secure version.
Isolate: If immediate patching is not possible, isolate the MCP server in a restricted network segment.
Restrict (Least Privilege): Limit the capabilities and permissions of the IAM roles used by the AWS CLI within the MCP environment. The node should only have access to the absolute minimum AWS resources required for its function.