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CVE-2026-16584: CVE-2026-16584: Security Policy Bypass in AWS API MCP Server via Startup Initialization Failure

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CVE-2026-16584: Security Policy Bypass in AWS API MCP Server via Startup Initialization Failure

Vulnerability ID: CVE-2026-16584
CVSS Score: 7.0
Published: 2026-07-24

A security policy bypass vulnerability exists in the AWS API MCP Server (awslabs-aws-api-mcp-server) from version 0.2.13 through 1.3.46. When the server fails to load the read-only operations index during startup (due to transient network failures, file permission issues, or other exceptions), it logs a warning but continues running in an insecure, degraded state. Under this condition, the security policy engine fails open, silently skipping all subsequent security checks and consent prompts for the lifetime of the process. This permits unauthorized mutating AWS CLI commands to execute via indirect prompt injection attacks.

TL;DR

The AWS API MCP Server fails open if the read-only operations index fails to load at startup, bypassing configured security policies and enabling unauthorized AWS command execution.

Technical Details

  • CWE ID: CWE-455 (Non-exit on Failed Initialization)
  • Attack Vector: Local (AV:L)
  • CVSS v3.1 Score: 7.0 (High)
  • CVSS v4.0 Score: 7.3 (High)
  • EPSS Score: 0.00130 (Percentile: 3.02%)
  • Exploit Status: None (No public weaponized exploits)
  • KEV Status: Not Listed

Affected Systems

  • awslabs-aws-api-mcp-server
  • awslabs-aws-api-mcp-server: >= 0.2.13, < 1.3.47 (Fixed in: 1.3.47)

Code Analysis

Commit: ab1bbeb

Fix security policy fail-open by raising startup exceptions and validating index availability at runtime

Mitigation Strategies

  • Upgrade the package to version 1.3.47 or later
  • Enforce the AWS IAM principle of least privilege on the server's active credentials
  • Deploy process monitoring to terminate the server if initialization warnings are detected

Remediation Steps:

  1. Identify all active deployments of awslabs-aws-api-mcp-server
  2. Execute pip install --upgrade 'awslabs-aws-api-mcp-server>=1.3.47' to apply the official patch
  3. Verify that the server successfully loads the operations index on startup
  4. Audit the associated AWS IAM role to ensure it only possesses necessary permissions

References

Read the full report for CVE-2026-16584 on our website for more details including interactive diagrams and full exploit analysis.

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