CVE-2025-5277: aws-mcp-server Command Injection RCE Flaw

CVE-2025-5277 Overview

CVE-2025-5277 is a critical command injection vulnerability discovered in the aws-mcp-server Model Context Protocol (MCP) server. An attacker can craft a malicious prompt that, when accessed by the MCP client, will execute arbitrary commands on the host system. This vulnerability affects systems running aws-mcp-server and allows remote attackers to gain full control over the underlying host through specially crafted inputs.

Critical Impact

This command injection vulnerability enables attackers to execute arbitrary system commands on hosts running aws-mcp-server, potentially leading to complete system compromise, data exfiltration, or lateral movement within affected environments.

Affected Products

• aws-mcp-server (versions prior to security fix)
• Systems utilizing aws-mcp-server MCP client integration
• AWS CLI automation environments using aws-mcp-server

Discovery Timeline

• May 28, 2025 - CVE-2025-5277 published to NVD
• May 28, 2025 - Last updated in NVD database

Technical Details for CVE-2025-5277

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 flaw exists in the cli_executor.py module of aws-mcp-server, specifically in how user-supplied input is processed before being passed to system command execution functions.

The vulnerability allows attackers to inject arbitrary operating system commands through crafted prompts submitted to the MCP client. When the MCP server processes these malicious prompts, it fails to properly sanitize or validate the input, allowing shell metacharacters and command separators to be interpreted by the underlying operating system. This can result in complete compromise of the host system, including unauthorized access to AWS credentials, data theft, and persistent backdoor installation.

Root Cause

The root cause of CVE-2025-5277 lies in insufficient input validation within the command execution pipeline. The cli_executor.py module did not properly validate or sanitize AWS commands and piped commands before execution. The security fix introduces dedicated validation functions (validate_aws_command and validate_pipe_command) from a new security module to ensure that all commands are properly vetted before execution, replacing the previous inadequate validate_unix_command function.

Attack Vector

The attack leverages the network-accessible MCP server interface. An attacker crafts a specially formatted prompt containing shell metacharacters or command injection payloads. When this prompt is processed by the MCP client and passed to the aws-mcp-server for execution, the malicious commands are executed with the privileges of the server process. This requires some user interaction (accessing the malicious prompt), but the attack can be performed remotely over the network.

The security patch demonstrates the fix approach by importing proper validation mechanisms:

from typing import TypedDict

from aws_mcp_server.config import DEFAULT_TIMEOUT, MAX_OUTPUT_SIZE
from aws_mcp_server.security import validate_aws_command, validate_pipe_command
from aws_mcp_server.tools import (
    CommandResult,
    execute_piped_command,
    is_pipe_command,
    split_pipe_command,
)

# Configure module logger

Source: GitHub Commit Details

Detection Methods for CVE-2025-5277

Indicators of Compromise

• Unusual process spawning from aws-mcp-server processes, particularly shell commands or unexpected binaries
• Anomalous network connections originating from the MCP server to external IP addresses
• Unexpected AWS API calls or credential access attempts from the server host
• Log entries containing shell metacharacters (;, |, &&, ||, `, $()) in MCP request parameters

Detection Strategies

• Monitor process execution chains for aws-mcp-server spawning unexpected child processes such as /bin/sh, /bin/bash, or common reconnaissance tools
• Implement application-level logging to capture all commands submitted to the MCP server for forensic analysis
• Deploy endpoint detection and response (EDR) solutions to identify command injection patterns in process arguments
• Configure SIEM rules to alert on anomalous command execution patterns from MCP server processes

Monitoring Recommendations

• Enable verbose logging on aws-mcp-server instances and forward logs to a centralized SIEM platform
• Implement network segmentation to limit the blast radius of potential compromises
• Monitor AWS CloudTrail for unusual API activity originating from systems running aws-mcp-server
• Set up alerts for process genealogy anomalies where python processes spawn shell interpreters

How to Mitigate CVE-2025-5277

Immediate Actions Required

• Update aws-mcp-server to the latest version that includes the security fix from commit 94d20ae
• Restrict network access to aws-mcp-server instances to trusted IP ranges only
• Audit existing deployments for signs of compromise before applying the patch
• Review and rotate any AWS credentials that may have been accessible to compromised systems

Patch Information

The security fix is available in the aws-mcp-server repository. The patch introduces a dedicated security module with validate_aws_command and validate_pipe_command functions to properly sanitize command inputs before execution. The fix also adds pyyaml>=6.0.0 as a new dependency. Organizations should update to the patched version immediately by pulling the latest code from the repository.

Workarounds

• Disable or isolate aws-mcp-server instances until the patch can be applied
• Implement network-level controls to restrict access to the MCP server from untrusted sources
• Deploy web application firewall (WAF) rules to filter requests containing common command injection patterns
• Run aws-mcp-server in a sandboxed container environment with restricted system call capabilities

# Configuration example - restrict aws-mcp-server to localhost only
# Update your configuration to bind to localhost
export AWS_MCP_SERVER_HOST="127.0.0.1"
export AWS_MCP_SERVER_PORT="8080"

# Alternatively, use firewall rules to restrict access
iptables -A INPUT -p tcp --dport 8080 -s 127.0.0.1 -j ACCEPT
iptables -A INPUT -p tcp --dport 8080 -j DROP